Entropy and life

From Wikipedia, the free encyclopedia

Research concerning the relationship between the thermodynamic quantity entropy and the evolution of life began around the turn of the 20th century. In 1910, American historian Henry Adams printed and distributed to university libraries and history professors the small volume A Letter to American Teachers of History proposing a theory of history based on the second law of thermodynamics and on the principle of entropy.^[1][2] The 1944 book What is Life? by Nobel-laureate physicist Erwin Schrödinger stimulated research in the field. In his book, Schrödinger originally stated that life feeds on negative entropy, or negentropy as it is sometimes called, but in a later edition corrected himself in response to complaints and stated the true source is free energy. More recent work has restricted the discussion to Gibbs free energy because biological processes on Earth normally occur at a constant temperature and pressure, such as in the atmosphere or at the bottom of an ocean, but not across both over short periods of time for individual organisms.

Origin

In 1863, Rudolf Clausius published his noted memoir "On the Concentration of Rays of Heat and Light, and on the Limits of its Action" wherein he outlined a preliminary relationship, as based on his own work and that of William Thomson (Lord Kelvin), between his newly developed concept of entropy and life.^{[citation needed]} Building on this, one of the first to speculate on a possible thermodynamic perspective of evolution was the Austrian physicist Ludwig Boltzmann. In 1875, building on the works of Clausius and Kelvin, Boltzmann reasoned:

The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, all abundantly available – nor for energy which exists in plenty in any body in the form of heat, but a struggle for [negative] entropy, which becomes available through the transition of energy from the hot sun to the cold earth.^[3]

Early views

In 1876, American civil engineer Richard Sears McCulloh, in his Treatise on the Mechanical Theory of Heat and its Application to the Steam-Engine, which was an early thermodynamics textbook, states, after speaking about the laws of the physical world, that "there are none that are established on a firmer basis than the two general propositions of Joule and Carnot; which constitute the fundamental laws of our subject." McCulloch then goes on to show that these two laws may be combined in a single expression as follows:

${\displaystyle S=\int {dQ \over \tau }}$

where

${\displaystyle S=}$ entropy

${\displaystyle dQ=}$ a differential amount of heat passed into a thermodynamic system

${\displaystyle \tau =}$ absolute temperature

McCulloch then declares that the applications of these two laws, i.e. what are currently known as the first law of thermodynamics and the second law of thermodynamics, are innumerable. He then states:

When we reflect how generally physical phenomena are connected with thermal changes and relations, it at once becomes obvious that there are few, if any, branches of natural science which are not more or less dependent upon the great truths under consideration. Nor should it, therefore, be a matter of surprise that already, in the short space of time, not yet one generation, elapsed since the mechanical theory of heat has been freely adopted, whole branches of physical science have been revolutionized by it.^{[4]:p. 267}

McCulloch then gives a few of what he calls the “more interesting examples” of the application of these laws in extent and utility. The first example he gives is physiology, wherein he states that “the body of an animal, not less than a steamer, or a locomotive, is truly a heat engine, and the consumption of food in the one is precisely analogous to the burning of fuel in the other; in both, the chemical process is the same: that called combustion.” He then incorporates a discussion of Lavoisier’s theory of respiration with cycles of digestion and excretion, perspiration, but then contradicts Lavoisier with recent findings, such as internal heat generated by friction, according to the new theory of heat, which, according to McCulloch, states that the “heat of the body generally and uniformly is diffused instead of being concentrated in the chest”. McCulloch then gives an example of the second law, where he states that friction, especially in the smaller blooded-vessels, must develop heat. Without doubt, animal heat is thus in part produced. He then asks: “but whence the expenditure of energy causing that friction, and which must be itself accounted for?"

To answer this question he turns to the mechanical theory of heat and goes on to loosely outline how the heart is what he calls a “force-pump”, which receives blood and sends it to every part of the body, as discovered by William Harvey, that “acts like the piston of an engine and is dependent upon and consequently due to the cycle of nutrition and excretion which sustains physical or organic life.” It is likely, here, that McCulloch was modeling parts of this argument on that of the famous Carnot cycle. In conclusion, he summarizes his first and second law argument as such:

Everything physical being subject to the law of conservation of energy, it follows that no physiological action can take place except with expenditure of energy derived from food; also, that an animal performing mechanical work must from the same quantity of food generate less heat than one abstaining from exertion, the difference being precisely the heat equivalent of that of work.^{[4]:p. 270}

Negative entropy

Later, building on this premise, in the famous 1944 book What is Life?, Nobel-laureate physicist Erwin Schrödinger theorizes that life, contrary to the general tendency dictated by the Second law of thermodynamics, decreases or maintains its entropy by feeding on negative entropy.^[5] In his note to Chapter 6 of What is Life?, however, Schrödinger remarks on his usage of the term negative entropy:

Let me say first, that if I had been catering for them [physicists] alone I should have let the discussion turn on free energy instead. It is the more familiar notion in this context. But this highly technical term seemed linguistically too near to energy for making the average reader alive to the contrast between the two things.

This is what is argued to differentiate life from other forms of matter organization. In this direction, although life's dynamics may be argued to go against the tendency of second law, which states that the entropy of an isolated system tends to increase, it does not in any way conflict or invalidate this law, because the principle that entropy can only increase or remain constant applies only to a closed system which is adiabatically isolated, meaning no heat can enter or leave. Whenever a system can exchange either heat or matter with its environment, an entropy decrease of that system is entirely compatible with the second law.^[6] The problem of organization in living systems increasing despite the second law is known as the Schrödinger paradox.^[7]

In 1964, James Lovelock was among a group of scientists who were requested by NASA to make a theoretical life detection system to look for life on Mars during the upcoming space mission. When thinking about this problem, Lovelock wondered “how can we be sure that Martian life, if any, will reveal itself to tests based on Earth’s lifestyle?”^[8] To Lovelock, the basic question was “What is life, and how should it be recognized?” When speaking about this issue with some of his colleagues at the Jet Propulsion Laboratory, he was asked what he would do to look for life on Mars. To this, Lovelock replied "I’d look for an entropy reduction, since this must be a general characteristic of life."^[8]

Gibbs free energy and biological evolution

In recent years, the thermodynamic interpretation of evolution in relation to entropy has begun to utilize the concept of the Gibbs free energy, rather than entropy.^[9] This is because biological processes on earth take place at roughly constant temperature and pressure, a situation in which the Gibbs free energy is an especially useful way to express the second law of thermodynamics. The Gibbs free energy is given by:

${\displaystyle \Delta G\equiv \Delta H-T\,\Delta S}$

The minimization of the Gibbs free energy is a form of the principle of minimum energy, which follows from the entropy maximization principle for closed systems. Moreover, the Gibbs free energy equation, in modified form, can be utilized for open systems when chemical potential terms are included in the energy balance equation. In a popular 1982 textbook, Principles of Biochemistry, noted American biochemist Albert Lehninger argues that the order produced within cells as they grow and divide is more than compensated for by the disorder they create in their surroundings in the course of growth and division. In short, according to Lehninger, "living organisms preserve their internal order by taking from their surroundings free energy, in the form of nutrients or sunlight, and returning to their surroundings an equal amount of energy as heat and entropy."^[10]

Similarly, according to the chemist John Avery, from his 2003 book Information Theory and Evolution, we find a presentation in which the phenomenon of life, including its origin and evolution, as well as human cultural evolution, has its basis in the background of thermodynamics, statistical mechanics, and information theory. The (apparent) paradox between the second law of thermodynamics and the high degree of order and complexity produced by living systems, according to Avery, has its resolution "in the information content of the Gibbs free energy that enters the biosphere from outside sources."^[11] The process of natural selection responsible for such local increase in order may be mathematically derived directly from the expression of the second law equation for connected non-equilibrium open systems.^[12]

Entropy and the origin of life

The second law of thermodynamics applied on the origin of life is a far more complicated issue than the further development of life, since there is no "standard model" of how the first biological lifeforms emerged; only a number of competing hypotheses. The problem is discussed within the area of abiogenesis, implying gradual pre-Darwinian chemical evolution. In 1924, Alexander Oparin suggested that sufficient energy was provided in a primordial soup. The Belgian scientist Ilya Prigogine was awarded with a Nobel prize in 1977 for an analysis in this area. A related topic is the probability that life would emerge, which has been discussed in several studies, for example by Russell Doolittle.^[13]

Entropy and the search for life elsewhere in the Universe

In 2013 Azua-Bustos and Vega argued that disregarding the type of lifeform that could be envisioned both on Earth and elsewhere in the Universe, all should share in common the attribute of being entities that decrease their internal entropy at the expense of free energy obtained from its surroundings. As entropy allows the quantification of the degree of disorder in a system, any envisioned lifeform must have a higher degree of order than its supporting environment. These authors showed that by using fractal mathematics analysis alone, they could readily quantify the degree of structural complexity difference (and thus entropy) of living processes as distinct entities separate from their similar abiotic surroundings. This approach may allow the future detection of unknown forms of life both in the Solar System and on recently discovered exoplanets based on nothing more than entropy differentials of complementary datasets (morphology, coloration, temperature, pH, isotopic composition, etc.). Detecting ‘life as we don't know it’ by fractal analysis

Other terms

For nearly a century and a half, beginning with Clausius' 1863 memoir "On the Concentration of Rays of Heat and Light, and on the Limits of its Action", much writing and research has been devoted to the relationship between thermodynamic entropy and the evolution of life. The argument that life feeds on negative entropy or negentropy was asserted by physicist Erwin Schrödinger in a 1944 book What is Life?. He posed, "How does the living organism avoid decay?" The obvious answer is: "By eating, drinking, breathing and (in the case of plants) assimilating." Recent writings have used the concept of Gibbs free energy to elaborate on this issue.^[14] While energy from nutrients is necessary to sustain an organism's order, there is also the Schrödinger prescience: "An organism's astonishing gift of concentrating a stream of order on itself and thus escaping the decay into atomic chaos – of drinking orderliness from a suitable environment – seems to be connected with the presence of the aperiodic solids..." We now know that the 'aperiodic' crystal is DNA and that the irregular arrangement is a form of information. "The DNA in the cell nucleus contains the master copy of the software, in duplicate. This software seems to control by "specifying an algorithm, or set of instructions, for creating and maintaining the entire organism containing the cell."^[15] DNA and other macromolecules determine an organism's life cycle: birth, growth, maturity, decline, and death. Nutrition is necessary but not sufficient to account for growth in size as genetics is the governing factor. At some point, organisms normally decline and die even while remaining in environments that contain sufficient nutrients to sustain life. The controlling factor must be internal and not nutrients or sunlight acting as causal exogenous variables. Organisms inherit the ability to create unique and complex biological structures; it is unlikely for those capabilities to be reinvented or be taught each generation. Therefore, DNA must be operative as the prime cause in this characteristic as well. Applying Boltzmann's perspective of the second law, the change of state from a more probable, less ordered and high entropy arrangement to one of less probability, more order, and lower entropy seen in biological ordering calls for a function like that known of DNA. DNA's apparent information processing function provides a resolution of the paradox posed by life and the entropy requirement of the second law.^[16]

In 1982, American biochemist Albert Lehninger argued that the "order" produced within cells as they grow and divide is more than compensated for by the "disorder" they create in their surroundings in the course of growth and division. "Living organisms preserve their internal order by taking from their surroundings free energy, in the form of nutrients or sunlight, and returning to their surroundings an equal amount of energy as heat and entropy."^[17]

Evolution-related concepts:

• Negentropy – a shorthand colloquial phrase for negative entropy.^[18]
• Ectropy – a measure of the tendency of a dynamical system to do useful work and grow more organized.^[19]
• Extropy – a metaphorical term defining the extent of a living or organizational system's intelligence, functional order, vitality, energy, life, experience, and capacity and drive for improvement and growth.
• Ecological entropy – a measure of biodiversity in the study of biological ecology.

In a study titled "Natural selection for least action" published in the Proceedings of the Royal Society A., Ville Kaila and Arto Annila of the University of Helsinki describe how the second law of thermodynamics can be written as an equation of motion to describe evolution, showing how natural selection and the principle of least action can be connected by expressing natural selection in terms of chemical thermodynamics. In this view, evolution explores possible paths to level differences in energy densities and so increase entropy most rapidly. Thus, an organism serves as an energy transfer mechanism, and beneficial mutations allow successive organisms to transfer more energy within their environment.^[20]

Objections

Entropy is defined for equilibrium systems,^[21] so objections to the extension of the second law and entropy to biological systems, especially as it pertains to its use to support or discredit the theory of evolution, have been stated.^[22] Live systems and indeed much of the systems and processes in the universe operate far from equilibrium, whereas the second law succinctly states that isolated systems evolve toward thermodynamic equilibrium — the state of maximum entropy.

However, entropy is well defined much more broadly based on the probabilities of a system's states, whether or not the system is a dynamical one (for which equilibrium could be relevant). Even in those physical systems where equilibrium could be relevant, (1) live systems cannot persist in isolation and (2) the second principle of thermodynamics does not require that free energy be transformed into entropy along the shortest path: live organisms absorb energy from sunlight or from energy-rich chemical compounds and finally return part of such energy to the environment as entropy (heat and low free-energy compounds such as water and CO₂).

Cosmic dust

From Wikipedia, the free encyclopedia

Porous chondrite interplanetary dust particle.

Cosmic dust, also called extraterrestrial dust or space dust, is dust which exists in outer space, as well as all over planet Earth.^[1][2] Most cosmic dust particles are between a few molecules to 0.1 µm in size. A smaller fraction of all dust in space consists of larger refractory minerals that condensed as matter left the stars. It is called "stardust" and is included in a separate section below. The dust density falling to Earth is approximately 10⁻⁶/m³ with each grain having a mass between 10⁻¹⁶kg (0.1 pg) and 10⁻⁴ kg (100 mg).^[3][4]

Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust (such as in the zodiacal cloud) and circumplanetary dust (such as in a planetary ring). In the Solar System, interplanetary dust causes the zodiacal light. Sources of Solar System dust include comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through the Solar System. The terminology has no specific application for describing materials found on the planet Earth except for dust that has demonstrably fallen to Earth. By one estimate, as much as 40,000 tons of cosmic dust reaches the Earth's surface every year.^[3] In October 2011, scientists reported that cosmic dust contains complex organic matter (amorphous organic solids with a mixed aromatic–aliphatic structure) that could be created naturally, and rapidly, by stars.^[5][6][7]

In August 2014, scientists announced the collection of possible interstellar dust particles from the Stardust spacecraft since returning to Earth in 2006.^{[8][9][10][11]} In March 2017, scientists reported that extraterrestrial dust particles have been identified all over planet Earth.^[2] According to one of the researchers, “Once I knew what to look for, I found them everywhere.”^[1]

Study and importance

Artist’s impression of dust formation around a supernova explosion.^[12]

Cosmic dust was once solely an annoyance to astronomers, as it obscures objects they wish to observe. When infrared astronomy began, the dust particles were observed to be significant and vital components of astrophysical processes. Their analysis can reveal information about phenomena like the formation of the Solar System.^[13] For example, cosmic dust can drive the mass loss when a star is nearing the end of its life, play a part in the early stages of star formation, and form planets. In the Solar System, dust plays a major role in the zodiacal light, Saturn's B Ring spokes, the outer diffuse planetary rings at Jupiter, Saturn, Uranus and Neptune, and comets.

Zodiacal light caused by cosmic dust.^[14]

The study of dust is a largely researched topic that brings together different scientific fields: physics (solid-state, electromagnetic theory, surface physics, statistical physics, thermal physics), fractal mathematics, chemistry (chemical reactions on grain surfaces), meteoritics, as well as every branch of astronomy and astrophysics.^[15] These disparate research areas can be linked by the following theme: the cosmic dust particles evolve cyclically; chemically, physically and dynamically. The evolution of dust traces out paths in which the Universe recycles material, in processes analogous to the daily recycling steps with which many people are familiar: production, storage, processing, collection, consumption, and discarding. Observations and measurements of cosmic dust in different regions provide an important insight into the Universe's recycling processes; in the clouds of the diffuse interstellar medium, in molecular clouds, in the circumstellar dust of young stellar objects, and in planetary systems such as the Solar System, where astronomers consider dust as in its most recycled state. The astronomers accumulate observational ‘snapshots’ of dust at different stages of its life and, over time, form a more complete movie of the Universe's complicated recycling steps.

Parameters such as the particle's initial motion, material properties, intervening plasma and magnetic field determined the dust particle's arrival at the dust detector. Slightly changing any of these parameters can give significantly different dust dynamical behavior. Therefore, one can learn about where that object came from, and what is (in) the intervening medium.

Detection methods

Cosmic dust of the Andromeda Galaxy as revealed in infrared light by the Spitzer Space Telescope.

Cosmic dust can be detected by indirect methods that utilize the radiative properties of the cosmic dust particles.

Cosmic dust can also be detected directly ('in-situ') using a variety of collection methods and from a variety of collection locations. Estimates of the daily influx of extraterrestrial material entering the Earth's atmosphere range between 5 and 300 tonnes. ^[16][17]

NASA collects samples of star dust particles in the Earth's atmosphere using plate collectors under the wings of stratospheric-flying airplanes. Dust samples are also collected from surface deposits on the large Earth ice-masses (Antarctica and Greenland/the Arctic) and in deep-sea sediments.

Don Brownlee at the University of Washington in Seattle first reliably identified the extraterrestrial nature of collected dust particles in the latter 1970s. Another source is the meteorites, which contain stardust extracted from them. Stardust grains are solid refractory pieces of individual presolar stars. They are recognized by their extreme isotopic compositions, which can only be isotopic compositions within evolved stars, prior to any mixing with the interstellar medium. These grains condensed from the stellar matter as it cooled while leaving the star.

Cosmic dust of the Horsehead Nebula as revealed by the Hubble Space Telescope.

In interplanetary space, dust detectors on planetary spacecraft have been built and flown, some are presently flying, and more are presently being built to fly. The large orbital velocities of dust particles in interplanetary space (typically 10–40 km/s) make intact particle capture problematic. Instead, in-situ dust detectors are generally devised to measure parameters associated with the high-velocity impact of dust particles on the instrument, and then derive physical properties of the particles (usually mass and velocity) through laboratory calibration (i.e. impacting accelerated particles with known properties onto a laboratory replica of the dust detector). Over the years dust detectors have measured, among others, the impact light flash, acoustic signal and impact ionisation. Recently the dust instrument on Stardust captured particles intact in low-density aerogel.

Dust detectors in the past flew on the HEOS-2, Helios, Pioneer 10, Pioneer 11, Giotto, and Galileo space missions, on the Earth-orbiting LDEF, EURECA, and Gorid satellites, and some scientists have utilized the Voyager 1 and 2 spacecraft as giant Langmuir probes to directly sample the cosmic dust. Presently dust detectors are flying on the Ulysses, Cassini, Proba, Rosetta, Stardust, and the New Horizons spacecraft. The collected dust at Earth or collected further in space and returned by sample-return space missions is then analyzed by dust scientists in their respective laboratories all over the world. One large storage facility for cosmic dust exists at the NASA Houston JSC.

Infrared light can penetrate the cosmic dust clouds, allowing us to peer into regions of star formation and the centers of galaxies. NASA's Spitzer Space Telescope is the largest infrared telescope ever launched into space. The Spitzer Space Telescope (formerly SIRTF, the Space Infrared Telescope Facility) was launched into space by a Delta rocket from Cape Canaveral, Florida on 25 August 2003. During its mission, Spitzer will obtain images and spectra by detecting the infrared energy, or heat, radiated by objects in space between wavelengths of 3 and 180 micrometres. Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground. The findings from the Spitzer already revitalized the studies of cosmic dust. A recent report from a Spitzer team shows some evidence that cosmic dust is formed near a supermassive black hole.^[18]

Another detection mechanism is polarimetry. Dust grains are not spherical and tend to align to interstellar magnetic fields, preferentially polarising starlight that passes through dust clouds. In nearby interstellar space, where cosmic reddening is not sensitive enough to be detected, high precision optical polarimetry has been used to glean the structure of dust within the Local Bubble.^[19]

Radiative properties

HH 151 is a bright jet of glowing material trailed by an intricate, orange-hued plume of gas and dust.^[20]

A dust particle interacts with electromagnetic radiation in a way that depends on its cross section, the wavelength of the electromagnetic radiation, and on the nature of the grain: its refractive index, size, etc. The radiation process for an individual grain is called its emissivity, dependent on the grain's efficiency factor. Furthermore, we have to specify whether the emissivity process is extinction, scattering, absorption, or polarisation. In the radiation emission curves, several important signatures identify the composition of the emitting or absorbing dust particles.

Dust particles can scatter light nonuniformly. Forward-scattered light means that light is redirected slightly by diffraction off its path from the star/sunlight, and back-scattered light is reflected light.

The scattering and extinction ("dimming") of the radiation gives useful information about the dust grain sizes. For example, if the object(s) in one's data is many times brighter in forward-scattered visible light than in back-scattered visible light, then we know that a significant fraction of the particles are about a micrometer in diameter.

The scattering of light from dust grains in long exposure visible photographs is quite noticeable in reflection nebulae, and gives clues about the individual particle's light-scattering properties. In X-ray wavelengths, many scientists are investigating the scattering of X-rays by interstellar dust, and some have suggested that astronomical X-ray sources would possess diffuse haloes, due to the dust.^[21]

Stardust

Stardust grains (also called presolar grains by meteoriticists^[22]) are contained within meteorites, from which they are extracted in terrestrial laboratories. Stardust was a component of the dust in the interstellar medium before its incorporation into meteorites. The meteorites have stored those stardust grains ever since the meteorites first assembled within the planetary accretion disk more than four billion years ago. So-called carbonaceous chondrites are especially fertile reservoirs of stardust. Each stardust grain existed before the Earth was formed. Stardust is a scientific term referring to refractory dust grains that condensed from cooling ejected gases from individual presolar stars and incorporated into the cloud from which the Solar System condensed.^[23]

Many different types of stardust have been identified by laboratory measurements of the highly unusual isotopic composition of the chemical elements that comprise each stardust grain. These refractory mineral grains may earlier have been coated with volatile compounds, but those are lost in the dissolving of meteorite matter in acids, leaving only insoluble refractory minerals. Finding the grain cores without dissolving most of the meteorite has been possible, but difficult and labor-intensive (see presolar grains).

Many new aspects of nucleosynthesis have been discovered from the isotopic ratios within the stardust grains.^[24] An important property of stardust is the hard, refractory, high-temperature nature of the grains. Prominent are silicon carbide, graphite, aluminium oxide, aluminium spinel, and other such solids that would condense at high temperature from a cooling gas, such as in stellar winds or in the decompression of the inside of a supernova. They differ greatly from the solids formed at low temperature within the interstellar medium.

Also important are their extreme isotopic compositions, which are expected to exist nowhere in the interstellar medium. This also suggests that the stardust condensed from the gases of individual stars before the isotopes could be diluted by mixing with the interstellar medium. These allow the source stars to be identified. For example, the heavy elements within the silicon carbide (SiC) grains are almost pure S-process isotopes, fitting their condensation within AGB star red giant winds inasmuch as the AGB stars are the main source of S-process nucleosynthesis and have atmospheres observed by astronomers to be highly enriched in dredged-up s process elements.

Another dramatic example is given by the so-called supernova condensates, usually shortened by acronym to SUNOCON (from SUperNOva CONdensate^[25]) to distinguish them from other stardust condensed within stellar atmospheres. SUNOCONs contain in their calcium an excessively large abundance^[26] of ⁴⁴Ca, demonstrating that they condensed containing abundant radioactive ⁴⁴Ti, which has a 65-year half-life. The outflowing ⁴⁴Ti nuclei were thus still "alive" (radioactive) when the SUNOCON condensed near one year within the expanding supernova interior, but would have become an extinct radionuclide (specifically ⁴⁴Ca) after the time required for mixing with the interstellar gas. Its discovery proved the prediction^[27] from 1975 that it might be possible to identify SUNOCONs in this way. The SiC SUNOCONs (from supernovae) are only about 1% as numerous as are SiC stardust from AGB stars.

Stardust itself (SUNOCONs and AGB grains that come from specific stars) is but a modest fraction of the condensed cosmic dust, forming less than 0.1% of the mass of total interstellar solids. The high interest in stardust derives from new information that it has brought to the sciences of stellar evolution and nucleosynthesis.

Laboratories have studied solids that existed before the Earth existed.^[28] This was once thought impossible, especially in the 1970s when cosmochemists were confident that the Solar System began as a hot gas^[29] virtually devoid of any remaining solids, which would have been vaporized by high temperature. The existence of stardust proved this historic picture incorrect.

Some bulk properties

Smooth chondrite interplanetary dust particle.

Cosmic dust is made of dust grains and aggregates of dust grains. These particles are irregularly shaped, with porosity ranging from fluffy to compact. The composition, size, and other properties depends on where the dust is found, and conversely, a compositional analysis of a dust particle can reveal much about the dust particle's origin. General diffuse interstellar medium dust, dust grains in dense clouds, planetary rings dust, and circumstellar dust, are each different in their characteristics. For example, grains in dense clouds have acquired a mantle of ice and on average are larger than dust particles in the diffuse interstellar medium. Interplanetary dust particles (IDPs) are generally larger still.

Major elements of 200 stratospheric interplanetary dust particles.

Most of the influx of extraterrestrial matter that falls onto the Earth is dominated by meteoroids with diameters in the range 50 to 500 micrometers, of average density 2.0 g/cm³ (with porosity about 40%). The densities of most IDPs captured in the Earth's stratosphere range between 1 and 3 g/cm³, with an average density at about 2.0 g/cm³.^[30]

Other specific dust properties:

• In circumstellar dust, astronomers have found molecular signatures of CO, silicon carbide, amorphous silicate, polycyclic aromatic hydrocarbons, water ice, and polyformaldehyde, among others (in the diffuse interstellar medium, there is evidence for silicate and carbon grains).
• Cometary dust is generally different (with overlap) from asteroidal dust. Asteroidal dust resembles carbonaceous chondritic meteorites. Cometary dust resembles interstellar grains which can include silicates, polycyclic aromatic hydrocarbons, and water ice.

Dust grain formation

The large grains in interstellar space are probably complex, with refractory cores that condensed within stellar outflows topped by layers acquired subsequently during incursions into cold dense interstellar clouds. That cyclic process of growth and destruction outside of the clouds has been modeled^[31][32] to demonstrate that the cores live much longer than the average lifetime of dust mass. Those cores mostly start with silicate particles condensing in the atmospheres of cool oxygen rich red-giant stars and carbon grains condensing in the atmospheres of cool carbon stars. The red-giant stars have evolved off the main sequence and have entered the giant phase of their evolution and are the major source of refractory dust grain cores in galaxies. Those refractory cores are also called Stardust (section above), which is a scientific term for the small fraction of cosmic dust that condensed thermally within stellar gases as they were ejected from the stars. Several percent of refractory grain cores have condensed within expanding interiors of supernovae, a type of cosmic decompression chamber. And meteoriticists that study this refractory stardust extracted from meteorites often call it presolar grains, although the refractory stardust that they study is actually only a small fraction of all presolar dust. Stardust condenses within the stars via considerably different condensation chemistry than that of the bulk of cosmic dust, which accretes cold onto preexisting dust in dark molecular clouds of the galaxy. Those molecular clouds are very cold, typically less than 50K, so that ices of many kinds may accrete onto grains, perhaps to be destroyed later. Finally, when the Solar System formed, interstellar dust grains were further modified by chemical reactions within the planetary accretion disk. So the history of the complex grains in the early Solar System is complicated and only partially understood.

Astronomers know that the dust is formed in the envelopes of late-evolved stars from specific observational signatures. In infrared light, emission at 9.7 micrometres is a signature of silicate dust in cool evolved oxygen-rich giant stars. Emission at 11.5 micrometres indicates the presence of silicon carbide dust in cool evolved carbon-rich giant stars. These help provide evidence that the small silicate particles in space came from the ejected outer envelopes of these stars.^[33][34]

Conditions in interstellar space are generally not suitable for the formation of silicate cores. This would take excessive time to accomplish, even if it might be possible. The arguments are that: given an observed typical grain diameter a, the time for a grain to attain a, and given the temperature of interstellar gas, it would take considerably longer than the age of the Universe for interstellar grains to form.^[35] On the other hand, grains are seen to have recently formed in the vicinity of nearby stars, in nova and supernova ejecta, and in R Coronae Borealis variable stars which seem to eject discrete clouds containing both gas and dust. So mass loss from stars is unquestionably where the refractory cores of grains formed.

Most dust in the Solar System is highly processed dust, recycled from the material out of which the Solar System formed and subsequently collected in the planetesimals, and leftover solid material such as comets and asteroids, and reformed in each of those bodies' collisional lifetimes. During the Solar System's formation history, the most abundant element was (and still is) H₂. The metallic elements: magnesium, silicon, and iron, which are the principal ingredients of rocky planets, condensed into solids at the highest temperatures of the planetary disk. Some molecules such as CO, N₂, NH₃, and free oxygen, existed in a gas phase. Some molecules, for example, graphite (C) and SiC would condense into solid grains in the planetary disk; but carbon and SiC grains found in meteorites are presolar based on their isotopic compositions, rather than from the planetary disk formation. Some molecules also formed complex organic compounds and some molecules formed frozen ice mantles, of which either could coat the "refractory" (Mg, Si, Fe) grain cores. Stardust once more provides an exception to the general trend, as it appears to be totally unprocessed since its thermal condensation within stars as refractory crystalline minerals. The condensation of graphite occurs within supernova interiors as they expand and cool, and do so even in gas containing more oxygen than carbon,^[36] a surprising carbon chemistry made possible by the intense radioactive environment of supernovae. This special example of dust formation has merited specific review.^[37]

Planetary disk formation of precursor molecules was determined, in large part, by the temperature of the solar nebula. Since the temperature of the solar nebula decreased with heliocentric distance, scientists can infer a dust grain's origin(s) with knowledge of the grain's materials. Some materials could only have been formed at high temperatures, while other grain materials could only have been formed at much lower temperatures. The materials in a single interplanetary dust particle often show that the grain elements formed in different locations and at different times in the solar nebula. Most of the matter present in the original solar nebula has since disappeared; drawn into the Sun, expelled into interstellar space, or reprocessed, for example, as part of the planets, asteroids or comets.

Due to their highly processed nature, IDPs (interplanetary dust particles) are fine-grained mixtures of thousands to millions of mineral grains and amorphous components. We can picture an IDP as a "matrix" of material with embedded elements which were formed at different times and places in the solar nebula and before the solar nebula's formation. Examples of embedded elements in cosmic dust are GEMS, chondrules, and CAIs.

From the solar nebula to Earth

A dusty trail from the early Solar System to carbonaceous dust today.

The arrows in the adjacent diagram show one possible path from a collected interplanetary dust particle back to the early stages of the solar nebula.

We can follow the trail to the right in the diagram to the IDPs that contain the most volatile and primitive elements. The trail takes us first from interplanetary dust particles to chondritic interplanetary dust particles. Planetary scientists classify chondritic IDPs in terms of their diminishing degree of oxidation so that they fall into three major groups: the carbonaneous, the ordinary, and the enstatite chondrites. As the name implies, the carbonaceous chondrites are rich in carbon, and many have anomalies in the isotopic abundances of H, C, N, and O (Jessberger, 2000)^{[citation needed]}. From the carbonaceous chondrites, we follow the trail to the most primitive materials. They are almost completely oxidized and contain the lowest condensation temperature elements ("volatile" elements) and the largest amount of organic compounds. Therefore, dust particles with these elements are thought to be formed in the early life of the Solar System. The volatile elements have never seen temperatures above about 500 K, therefore, the IDP grain "matrix" consists of some very primitive Solar System material. Such a scenario is true in the case of comet dust.^[38] The provenance of the small fraction that is stardust (see above) is quite different; these refractory interstellar minerals thermally condense within stars, become a small component of interstellar matter, and therefore remain in the presolar planetary disk. Nuclear damage tracks are caused by the ion flux from solar flares. Solar wind ions impacting on the particle's surface produce amorphous radiation damaged rims on the particle's surface. And spallogenic nuclei are produced by galactic and solar cosmic rays. A dust particle that originates in the Kuiper Belt at 40 AU would have many more times the density of tracks, thicker amorphous rims and higher integrated doses than a dust particle originating in the main-asteroid belt.

Based on 2012 computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth.^[39] According to the computer studies, this same process may also occur around other stars that acquire planets.^[39] (Also see Extraterrestrial organic molecules.)

In September 2012, NASA scientists reported that polycyclic aromatic hydrocarbons (PAHs), subjected to interstellar medium (ISM) conditions, are transformed, through hydrogenation, oxygenation and hydroxylation, to more complex organics - "a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively".^[40][41] Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."^[40][41]

In February 2014, NASA announced a greatly upgraded database^[42] for detecting and monitoring polycyclic aromatic hydrocarbons (PAHs) in the universe. According to NASA scientists, over 20% of the carbon in the Universe may be associated with PAHs, possible starting materials for the formation of life.^[42] PAHs seem to have been formed shortly after the Big Bang, are abundant in the Universe,^[43][44][45] and are associated with new stars and exoplanets.^[42]

In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the Universe, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists.^[46]

Some "dusty" clouds in the universe

The Solar System has its own interplanetary dust cloud, as do extrasolar systems.

There are different types of nebulae with different physical causes and processes. One might see these classifications:

• diffuse nebula
• infrared (IR) reflection nebula
• supernova remnant
• molecular cloud
• HII regions
• photodissociation regions
• Dark Nebula

Distinctions between those types of nebula are that different radiation processes are at work. For example, H II regions, like the Orion Nebula, where a lot of star-formation is taking place, are characterized as thermal emission nebulae. Supernova remnants, on the other hand, like the Crab Nebula, are characterized as nonthermal emission (synchrotron radiation).

Some of the better known dusty regions in the Universe are the diffuse nebulae in the Messier catalog, for example: M1, M8, M16, M17, M20, M42, M43.^[47]

Some larger dust catalogs are:

• Sharpless (1959) A Catalogue of HII Regions
• Lynds (1965) Catalogue of Bright Nebulae
• Lunds (1962) Catalogue of Dark Nebulae
• van den Bergh (1966) Catalogue of Reflection Nebulae
• Green (1988) Rev. Reference Cat. of Galactic SNRs
• The National Space Sciences Data Center (NSSDC)
• CDS Online Catalogs

Interstellar dust sample return

In the spring of 2014, the recovery of particles of interstellar dust from the Discovery program's Stardust mission was announced.^[48]

The “Threat” of Creationism by Isaac Asimov

The following essay was published in Science and Creationism (1984).
Original link:  http://www.stephenjaygould.org/ctrl/azimov_creationism.html

Scientists thought it was settled. The universe, they had decided, is about 20 billion years old, and Earth itself is 4.5 billion years old. Simple forms of life came into being more than three billion years ago, having formed spontaneously from nonliving matter. They grew more complex through slow evolutionary processes and the first hominid ancestors of humanity appeared more than four million years ago. Homo sapians itself—the present human species, people like you and me—has walked the earth for at least 50,000 years.

But apparently it isn't settled. There are Americans who believe that the earth is only about 6,000 years old; that human beings and all other species were brought into existence by a divine Creator as eternally separate variations of beings; and that there has been no evolutionary process.

They are creationists—they call themselves "scientific" creationists—and they are a growing power in the land, demanding that schools be forced to teach their views. State legislatures, mindful of the votes, are beginning to succumb to the pressure. In perhaps 15 states, bills have been introduced, putting forth the creationist point of view, and in others, strong movements are gaining momentum. In Arkansas, a law requiring that the teaching of creationism receive equal time was passed this spring and is scheduled to go into effect in September 1982, though the American Civil Liberties Union has filed suit on behalf of a group of clergymen, teachers, and parents to overturn it. And a California father named Kelly Segraves, the director of the Creation-Science Research Center, sued to have public-school science classes taught that there are other theories of creation besides evolution, and that one of them was the Biblical version. The suit came to trial in March, and the judge ruled that educators must distribute a policy statement to schools and textbook publishers explaining that the theory of evolution should not be seen as "the ultimate cause of origins." Even in New York, the Board of Education has delayed since January in making a final decision, expected this month [June 1981], on whether schools will be required to include the teaching of creationism in their curriculums.

The Rev. Jerry Fallwell, the head of the Moral Majority, who supports the creationist view from his television pulpit, claims that he has 17 million to 25 million viewers (though Arbitron places the figure at a much more modest 1.6 million). But there are 66 electronic ministries which have a total audience of about 20 million. And in parts of the country where the Fundamentalists predominate—the so called Bible Belt— creationists are in the majority.

They make up a fervid and dedicated group, convinced beyond argument of both their rightness and their righteousness. Faced with an apathetic and falsely secure majority, smaller groups have used intense pressure and forceful campaigning—as the creationists do—and have succeeded in disrupting and taking over whole societies.

Yet, though creationists seem to accept the literal truth of the Biblical story of creation, this does not mean that all religious people are creationists. There are millions of Catholics, Protestants, and Jews who think of the Bible as a source of spiritual truth and accept much of it as symbolically rather than literally true. They do not consider the Bible to be a textbook of science, even in intent, and have no problem teaching evolution in their secular institutions.

To those who are trained in science, creationism seems like a bad dream, a sudden reliving of a nightmare, a renewed march of an army of the night risen to challenge free thought and enlightenment.

The scientific evidence for the age of the earth and for the evolutionary development of life seems overwhelming to scientists. How can anyone question it? What are the arguments the creationists use? What is the "science" that makes their views "scientific"? Here are some of them:

»  The argument from analogy.

A watch implies a watchmaker, say the creationists. If you were to find a beautifully intricate watch in the desert, far from habitation, you would be sure that it had been fashioned by human hands and somehow left there. It would pass the bounds of credibility that it had simply formed, spontaneously, from the sands of the desert.

By analogy, then, if you consider humanity, life, Earth, and the universe, all infinitely more intricate than a watch, you can believe far less easily that it "just happened." It, too, like the watch, must have been fashioned, but by more-than-human hands—in short by a divine Creator.

This argument seems unanswerable, and it has been used (even though not often explicitly expressed) ever since the dawn of consciousness. To have explained to prescientific human beings that the wind and the rain and the sun follow the laws of nature and do so blindly and without a guiding would have been utterly unconvincing to them. In fact, it might have well gotten you stoned to death as a blasphemer.

There are many aspects of the universe that still cannot be explained satisfactorily by science; but ignorance only implies ignorance that may someday be conquered. To surrender to ignorance and call it God has always been premature, and it remains premature today.

In short, the complexity of the universe—and one's inability to explain it in full—is not in itself an argument for a Creator.

»  The argument from general consent.

Some creationists point out that belief in a Creator is general among all peoples and all cultures. Surly this unanimous craving hints at a greater truth. There would be no unanimous belief in a lie.

General belief, however, is not really surprising. Nearly every people on earth that considers the existence of the world assumes it to have been created by a god or gods. And each group invents full details for the story. No two creation tales are alike. The Greeks, the Norsemen, the Japanese, the Hindus, the American Indians, and so on and so on all have their own creation myths, and all of these are recognized by Americans of Judeo-Christian heritage as "just myths."

The ancient Hebrews also had a creation tale—two of them, in fact. There is a primitive Adam-and-Eve-in-Paradise story, with man created first, then animals, then woman. There is also a poetic tale of God fashioning the universe in six days, with animals preceding man, and man and woman created together.

These Hebrew myths are not inherently more credible than any of the others, but they are our myths. General consent, of course, proves nothing: There can be a unanimous belief in something that isn't so. The universal opinion over thousands of years that the earth was flat never flattened its spherical shape by one inch.

»  The argument of belittlement.

Creationists frequently stress the fact that evolution is "only a theory," giving the impression that a theory is an idle guess. A scientist, one gathers, arising one morning with nothing particular to do, decided that perhaps the moon is made of Roquefort cheese and instantly advances the Roquefort-cheese theory.

A theory (as the word is used by scientists) is a detailed description of some facet of the universe's workings that is based on long observation and, where possible, experiment. It is the result of careful reasoning from these observations and experiments that has survived the critical study of scientists generally.

For example, we have the description of the cellular nature of living organisms (the "cell theory"); of objects attracting each other according to fixed rule (the "theory of gravitation"); of energy behaving in discrete bits (the "quantum theory"); of light traveling through a vacuum at a fixed measurable velocity (the "theory of relativity"), and so on.

All are theories; all are firmly founded; all are accepted as valid descriptions of this or that aspect of the universe. They are neither guesses nor speculations. And no theory is better founded, more closely examined, more critically argued and more thoroughly accepted, than the theory of evolution. If it is "only" a theory, that is all it has to be.

Creationism, on the other hand, is not a theory. There is no evidence, in the scientific sense, that supports it. Creationism, or at least the particular variety accepted by many Americans, is an expression of early Middle Eastern legend. It is fairly described as "only a myth."

»  The argument of imperfection.

Creationists, in recent years, have stressed the "scientific" background of their beliefs. They point out that there are scientists who base their creationist beliefs on a careful study of geology, paleontology, and biology and produce "textbooks" that embody those beliefs.

Virtually the whole scientific corpus of creationism, however, consists of the pointing out of imperfections in the evolutionary view. The creationists insist, for example, that evolutionists cannot show true transition states between species in the fossil evidence; that age determinations through radioactive breakdown are uncertain; that alternative interpretations of this or that piece of evidence are possible and so on.

Because the evolutionary view is not perfect and is not agreed upon by all scientists, creationists argue that evolution is false and that scientists, in supporting evolution, are basing their views on blind faith and dogmatism.

To an extent, the creationists are right here: The details of evolution are not perfectly known. Scientists have been adjusting and modifying Charles Darwin's suggestions since he advanced his theory of the origin of species through natural selection back in 1859. After all, much has been learned about the fossil record and physiology, microbiology, biochemistry, ethology, and various other branches of life science in the last 125 years, and it was to be expected that we can improve on Darwin. In fact, we have improved on him. Nor is the process finished. it can never be, as long as human beings continue to question and to strive for better answers.

The details of evolutionary theory are in dispute precisely because scientists are not devotees of blind faith and dogmatism. They do not accept even as great a thinker as Darwin without question, nor do they accept any idea, new or old, without thorough argument. Even after accepting an idea, they stand ready to overrule it, if appropriate new evidence arrives. If, however, we grant that a theory is imperfect and details remain in dispute, does that disprove the theory as a whole?

Consider. I drive a car, and you drive a car. I do not know exactly how an engine works. Perhaps you do not either. And it may be that our hazy and approximate ideas of the workings of an automobile are in conflict. Must we then conclude from this disagreement that an automobile does not run, or that it does not exist? Or, if our senses force us to conclude that an automobile does exist and run, does that mean it is pulled by an invisible horse, since our engine theory is imperfect?

However much scientists argue their differing beliefs in details of evolutionary theory, or in the interpretation of the necessarily imperfect fossil record, they firmly accept the evolutionary process itself.

»  The argument from distorted science.

Creationists have learned enough scientific terminology to use it in their attempts to disprove evolution. They do this in numerous ways, but the most common example, at least in the mail I receive is the repeated assertion that the second law of thermodynamics demonstrates the evolutionary process to be impossible.

In kindergarten terms, the second law of thermodynamics says that all spontaneous change is in the direction of increasing disorder—that is, in a "downhill" direction. There can be no spontaneous buildup of the complex from the simple, therefore, because that would be moving "uphill." According to the creationists argument, since, by the evolutionary process, complex forms of life evolve from simple forms, that process defies the second law, so creationism must be true.

Such an argument implies that this clearly visible fallacy is somehow invisible to scientists, who must therefore be flying in the face of the second law through sheer perversity. Scientists, however, do know about the second law and they are not blind. It's just that an argument based on kindergarten terms is suitable only for kindergartens.

To lift the argument a notch above the kindergarten level, the second law of thermodynamics applies to a "closed system"—that is, to a system that does not gain energy from without, or lose energy to the outside. The only truly closed system we know of is the universe as a whole.

Within a closed system, there are subsystems that can gain complexity spontaneously, provided there is a greater loss of complexity in another interlocking subsystem. The overall change then is a complexity loss in line with the dictates of the second law.

Evolution can proceed and build up the complex from the simple, thus moving uphill, without violating the second law, as long as another interlocking part of the system — the sun, which delivers energy to the earth continually — moves downhill (as it does) at a much faster rate than evolution moves uphill. If the sun were to cease shining, evolution would stop and so, eventually, would life.

Unfortunately, the second law is a subtle concept which most people are not accustomed to dealing with, and it is not easy to see the fallacy in the creationist distortion.

There are many other "scientific" arguments used by creationists, some taking quite clever advantage of present areas of dispute in evolutionary theory, but every one of then is as disingenuous as the second-law argument.

The "scientific" arguments are organized into special creationist textbooks, which have all the surface appearance of the real thing, and which school systems are being heavily pressured to accept. They are written by people who have not made any mark as scientists, and, while they discuss geology, paleontology and biology with correct scientific terminology, they are devoted almost entirely to raising doubts over the legitimacy of the evidence and reasoning underlying evolutionary thinking on the assumption that this leaves creationism as the only possible alternative.

Evidence actually in favor of creationism is not presented, of course, because none exists other than the word of the Bible, which it is current creationist strategy not to use.

»  The argument from irrelevance.

Some creationists put all matters of scientific evidence to one side and consider all such things irrelevant. The Creator, they say, brought life and the earth and the entire universe into being 6,000 years ago or so, complete with all the evidence for eons-long evolutionary development. The fossil record, the decaying radio activity, the receding galaxies were all created as they are, and the evidence they present is an illusion.

Of course, this argument is itself irrelevant, for it can be neither proved nor disproved. It is not an argument, actually, but a statement. I can say that the entire universe was created two minutes age, complete with all its history books describing a nonexistent past in detail, and with every living person equipped with a full memory; you, for instance, in the process of reading this article in midstream with a memory of what you had read in the beginning—which you had not really read.

What kind of Creator would produce a universe containing so intricate an illusion? It would mean that the Creator formed a universe that contained human beings whom He had endowed with the faculty of curiosity and the ability to reason. He supplied those human beings with an enormous amount of subtle and cleverly consistent evidence designed to mislead them and cause them to be convinced that the universe was created 20 billion years ago and developed by evolutionary processes that include the creation and the development of life on Earth. Why?

Does the Creator take pleasure in fooling us? Does it amuse Him to watch us go wrong? Is it part of a test to see if human beings will deny their senses and their reason in order to cling to myth? Can it be that the Creator is a cruel and malicious prankster, with a vicious and adolescent sense of humor?

»  The argument from authority.

The Bible says that God created the world in six days, and the Bible is the inspired word of God. To the average creationist this is all that counts. All other arguments are merely a tedious way of countering the propaganda of all those wicked humanists, agnostics, and atheists who are not satisfied with the clear word of the Lord.

The creationist leaders do not actually use that argument because that would make their argument a religious one, and they would not be able to use it in fighting a secular school system. They have to borrow the clothing of science, no matter how badly it fits, and call themselves "scientific" creationists. They also speak only of the "Creator," and never mentioned that this Creator is the God of the Bible.

We cannot, however, take this sheep's clothing seriously. However much the creationist leaders might hammer away at in their "scientific" and "philosophical" points, they would be helpless and a laughing-stock if that were all they had.

It is religion that recruits their squadrons. Tens of millions of Americans, who neither know nor understand the actual arguments for or even against evolution, march in the army of the night with their Bibles held high. And they are a strong and frightening force, impervious to, and immunized against, the feeble lance of mere reason.

Even if I am right and the evolutionists' case is very strong, have not creationists, whatever the emptiness of their case, a right to be heard? if their case is empty, isn't it perfectly safe to discuss it since the emptiness would then be apparent? Why, then are evolutionists so reluctant to have creationism taught in the public schools on an equal basis with evolutionary theory? can it be that the evolutionists are not as confident of their case as they pretend. Are they afraid to allow youngsters a clear choice?

First, the creationists are somewhat less than honest in their demand for equal time. It is not their views that are repressed: schools are by no means the only place in which the dispute between creationism and evolutionary theory is played out. There are churches, for instance, which are a much more serious influence on most Americans than the schools are. To be sure, many churches are quite liberal, have made their peace with science and find it easy to live with scientific advance—even with evolution. But many of the less modish and citified churches are bastions of creationism.

The influence of the church is naturally felt in the home, in the newspapers, and in all of surrounding society. It makes itself felt in the nation as a whole, even in religiously liberal areas, in thousands of subtle ways: in the nature of holiday observance, in expressions of patriotic fervor, even in total irrelevancies. In 1968, for example, a team of astronomers circling the moon were instructed to read the first few verses of Genesis as though NASA felt it had to placate the public lest they rage against the violation of the firmament. At the present time, even the current President of the United States has expressed his creationist sympathies.

It is only in school that American youngsters in general are ever likely to hear any reasoned exposition of the evolutionary viewpiont. They might find such a viewpoint in books, magazines, newspapers, or even, on occasion, on television. But church and family can easily censor printed matter or television. Only the school is beyond their control.

But only just barely beyond. Even though schools are now allowed to teach evolution, teachers are beginning to be apologetic about it, knowing full well their jobs are at the mercy of school boards upon which creationists are a stronger and stronger influence.

Then, too, in schools, students are not required to believe what they learn about evolution—merely to parrot it back on test. If they fail to do so, their punishment is nothing more than the loss of a few points on a test or two.

In the creationist churches, however, the congregation is required to believe. Impressionable youngsters, taught that they will go to hell if they listen to the evolutionary doctrine, are not likely to listen in comfort or to believe if they do. Therefore, creationists, who control the church and the society they live in and to face the public-school as the only place where evolution is even briefly mentioned in a possible favorable way, find they cannot stand even so minuscule a competition and demand "equal time."

Do you suppose their devotion to "fairness" is such that they will give equal time to evolution in their churches?

Second, the real danger is the manner in which creationists want their "equal time." In the scientific world, there is free and open competition of ideas, and even a scientist whose suggestions are not accepted is nevertheless free to continue to argue his case. In this free and open competition of ideas, creationism has clearly lost. It has been losing, in fact, since the time of Copernicus four and a half centuries ago. But creationists, placing myth above reason, refuse to accept the decision and are now calling on the government to force their views on the schools in lieu of the free expression of ideas. Teachers must be forced to present creationism as though it had equal intellectual respectability with evolutionary doctrine.

What a precedent this sets.

If the government can mobilize its policemen and its prisons to make certain that teachers give creationism equal time, they can next use force to make sure that teachers declare creationism the victor so that evolution will be evicted from the classroom altogether. We will have established the full ground work, in other words, for legally enforced ignorance and for totalitarian thought control. And what if the creationists win? They might, you know, for there are millions who, faced with a choice between science and their interpretation of the Bible, will choose the Bible and reject science, regardless of the evidence.

This is not entirely because of the traditional and unthinking reverence for the literal words of the Bible; there is also a pervasive uneasiness—even an actual fear—of science that will drive even those who care little for fundamentalism into the arms of the creationists. For one thing, science is uncertain. Theories are subject to revision; observations are open to a variety of interpretations, and scientists quarrel among themselves. This is disillusioning for those untrained in the scientific method, who thus turn to the rigid certainty of the Bible instead. There is something comfortable about a view that allows for no deviation and that spares you the painful necessity of having to think.

Second, science is complex and chilling. The mathematical language of science is understood by very few. The vistas it presents are scary—an enormous universe ruled by chance and impersonal rules, empty and uncaring, ungraspable and vertiginous. How comfortable to turn instead to a small world, only a few thousand years old, and under God's personal and immediate care; a world in which you are His particular concern and where He will not consign you to hell if you are careful to follow every word of the Bible as interpreted for you by your television preacher.

Third, science is dangerous. There is no question but that poison gas, genetic engineering, and nuclear weapons and power stations are terrifying. It may be that civilization is falling apart and the world we know is coming to an end. In that case, why not turn to religion and look forward to the Day of Judgment, in which you and your fellow believers will be lifted into eternal bliss and have the added joy of watching the scoffers and disbelievers writhe forever in torment.

So why might they not win?

There are numerous cases of societies in which the armies of the night have ridden triumphantly over minorities in order to establish a powerful orthodoxy which dictates official thought. Invariably, the triumphant ride is toward long-range disaster. Spain dominated Europe and the world in the 16th century, but in Spain orthodoxy came first, and all divergence of opinion was ruthlessly suppressed. The result was that Spain settled back into blankness and did not share in the scientific, technological and commercial ferment that bubbled up in other nations of Western Europe. Spain remained an intellectual backwater for centuries. In the late 17th century, France in the name of orthodoxy revoked the Edict of Nantes and drove out many thousands of Huguenots, who added their intellectual vigor to lands of refuge such as Great Britain, the Netherlands, and Prussia, while France was permanently weakened.

In more recent times, Germany hounded out the Jewish scientists of Europe. They arrived in the United States and contributed immeasurably to scientific advancement here, while Germany lost so heavily that there is no telling how long it will take it to regain its former scientific eminence. The Soviet Union, in its fascination with Lysenko, destroyed its geneticists, and set back its biological sciences for decades. China, during the Cultural Revolution, turned against Western science and is still laboring to overcome the devastation that resulted.

Are we now, with all these examples before us, to ride backward into the past under the same tattered banner of orthodoxy? With creationism in the saddle, American science will wither. We will raise a generation of ignoramuses ill-equipped to run the industry of tomorrow, much less to generate the new advances of the days after tomorrow.

We will inevitably recede into the backwater of civilization, and those nations that retain opened scientific thought will take over the leadership of the world and the cutting edge of human advancement. I don't suppose that the creationists really plan the decline of the United States, but their loudly expressed patriotism is as simpleminded as their "science." If they succeed, they will, in their folly, achieve the opposite of what they say they wish.