Philosophical skepticism

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Philosophical skepticism (UK spelling: scepticism; from Greek σκέψις skepsis, "inquiry") is a philosophical school of thought that questions the possibility of certainty in knowledge. Skeptic philosophers from different historical periods adopted different principles and arguments, but their ideology can be generalized as either (1) the denial of possibility of all knowledge or (2) the suspension of judgement due to the inadequacy of evidence.

Philosophy of skepticism

Skepticism is not a single position but covers a range of different positions. In the ancient world there were two main skeptical traditions. Academic skepticism took the dogmatic position that knowledge was not possible; Pyrrhonian skeptics refused to take a dogmatic position on any issue—including skepticism. Radical skepticism ends in the paradoxical claim that one cannot know anything—including that one cannot know about knowing anything.

Skepticism can be classified according to its scope. Local skepticism involves being skeptical about particular areas of knowledge, e.g. moral skepticism, skepticism about the external world, or skepticism about other minds, whereas global skepticism is skeptical about the possibility of any knowledge at all.

Skepticism can also be classified according to its method. In the Western tradition there are two basic approaches to skepticism. Cartesian skepticism —named somewhat misleadingly after René Descartes, who was not a skeptic but used some traditional skeptical arguments in his Meditations to help establish his rationalist approach to knowledge— attempts to show that any proposed knowledge claim can be doubted. Agrippan skepticism focuses on the process of justification rather than the possibility of doubt. According to this view there are three ways in which one might attempt to justify a claim but none of them are adequate: one can keep on providing further justification but this leads to an infinite regress; one can stop at a dogmatic assertion; or one can argue in circular reasoning, never reaching a viable conclusion.

Philosophical skepticism is distinguished from methodological skepticism in that philosophical skepticism is an approach that questions the possibility of certainty in knowledge, whereas methodological skepticism is an approach that subjects all knowledge claims to scrutiny with the goal of sorting out true from false claims.

Schools

Philosophical skepticism begins with the claim that the skeptic currently does not have knowledge. Some adherents maintain that knowledge is, in theory, possible. It could be argued that Socrates held that view. He appears to have thought that if people continue to ask questions they might eventually come to have knowledge; but that they did not have it yet. Some skeptics have gone further and claimed that true knowledge is impossible, for example the Academic school in Ancient Greece well after the time of Carneades. A third skeptical approach would be neither to accept nor reject the possibility of knowledge.

Skepticism can be either about everything or about particular areas. A 'global' skeptic argues that he does not absolutely know anything to be either true or false. Academic global skepticism has great difficulty in supporting this claim while maintaining philosophical rigor, since it seems to require that nothing can be known—except for the knowledge that nothing can be known, though in its probabilistic form it can use and support the notion of weight of evidence. Thus, some probabilists avoid extreme skepticism by maintaining that they merely are 'reasonably certain' (or 'largely believe') some things are real or true. As for using probabilistic arguments to defend skepticism, in a sense this enlarges or increases scepticism, while the defence of empiricism by Empiricus weakens skepticism and strengthens dogmatism by alleging that sensory appearances are beyond doubt. Much later, Kant would re-define "dogmatism" to make indirect realism about the external world seem objectionable. While many Hellenists, outside of Empiricus, would maintain that everyone who is not sceptical about everything is a dogmatist, this position would seem too extreme for most later philosophers.

Nevertheless, A Pyrrhonian global skeptic labors under no such modern constraint, since he only alleged that he, personally, did not know anything and made no statement about the possibility of knowledge. Nor did Arcesilaus feel bound, since he merely corrected Socrates's "I only know that I know nothing" by adding "I don't even know that", thus more fully rejecting dogmatism.
Local skeptics deny that people do or can have knowledge of a particular area. They may be skeptical about the possibility of one form of knowledge without doubting other forms. Different kinds of local skepticism may emerge, depending on the area. A person may doubt the truth value of different types of journalism, for example, depending on the types of media they trust.

In Islamic philosophy, skepticism was established by Al-Ghazali (1058–1111), known in the West as "Algazel", as part of the Ash'ari school of Islamic theology.

Francisco Sanches's That Nothing is Known (published in 1581 as Quod nihil scitur) is one of the crucial texts of Renaissance skepticism.

Epistemology and skepticism

Skepticism, as an epistemological argument, poses the question of whether knowledge, in the first place, is possible. Skeptics argue that the belief in something does not necessarily justify an assertion of knowledge of it. In this, skeptics oppose dogmatic foundationalism, which states that there have to be some basic positions that are self-justified or beyond justification, without reference to others. (One example of such foundationalism may be found in Spinoza's Ethics.) The skeptical response to this can take several approaches. First, claiming that "basic positions" must exist amounts to the logical fallacy of argument from ignorance combined with the slippery slope.

Among other arguments, skeptics used Agrippa's trilemma, named after Agrippa the Sceptic, to claim no certain belief could be achieved. Foundationalists have used the same trilemma as a justification for demanding the validity of basic beliefs.

This skeptical approach is rarely taken to its pyrrhonean extreme by most practitioners. Several modifications have arisen over the years, including the following:

Fictionalism would not claim to have knowledge but will adhere to conclusions on some criterion such as utility, aesthetics, or other personal criteria without claiming that any conclusion is actually "true".

Philosophical fideism (as opposed to religious Fideism) would assert the truth of some propositions, but does so without asserting certainty.

Some forms of pragmatism would accept utility as a provisional guide to truth but not necessarily a universal decision-maker.

There are two different categories of epistemological skepticism, which can be referred to as mitigated and unmitigated skepticism. The two forms are contrasting but are still true forms of skepticism. Mitigated skepticism does not accept "strong" or "strict" knowledge claims but does, however, approve specific weaker ones. These weaker claims can be assigned the title of "virtual knowledge", but must be to justified belief. Unmitigated skepticism rejects both claims of virtual knowledge and strong knowledge. Characterising knowledge as strong, weak, virtual or genuine can be determined differently depending on a person's viewpoint as well as their characterisation of knowledge.

Criticism of skepticism

Most philosophies have weaknesses and can be criticized and this is a general principle of progression in philosophy. The philosophy of skepticism asserts that no truth is knowable or only probable. Some say the scientific method also asserts probable findings, because the number of cases tested is always limited and they constitute perceptual observations. Another criticism is the proposition that “no truth is knowable” is knowably true is contradictory. The here is one hand argument is also another relatively simple criticism that reverses the skeptic's proposals and supports common sense.

Pierre Le Morvan (2011) has distinguished between three broad philosophical approaches to skepticism. The first he calls the "Foil Approach." According to the latter, skepticism is treated as a problem to be solved, or challenge to be met, or threat to be parried; skepticism‘s value on this view, insofar as it is deemed to have one, accrues from its role as a foil contrastively illuminating what is required for knowledge and justified belief. The second he calls the "Bypass Approach" according to which skepticism is bypassed as a central concern of epistemology. Le Morvan advocates a third approach—he dubs it the "Health Approach"—that explores when skepticism is healthy and when it is not, or when it is virtuous and when it is vicious.

Skeptical hypotheses

A skeptical hypothesis is a hypothetical situation which can be used in an argument for skepticism about a particular claim or class of claims. Usually the hypothesis posits the existence of a deceptive power that deceives our senses and undermines the justification of knowledge otherwise accepted as justified. Skeptical hypotheses have received much attention in modern Western philosophy.

The first skeptical hypothesis in modern Western philosophy appears in René Descartes' Meditations on First Philosophy. At the end of the first Meditation Descartes writes: "I will suppose... that some evil demon of the utmost power and cunning has employed all his energies to deceive me."

• The "brain in a vat" hypothesis is cast in scientific terms. It supposes that one might be a disembodied brain kept alive in a vat, and fed false sensory signals, by a mad scientist.
• The "dream argument" of Descartes and Zhuangzi supposes reality to be indistinguishable from a dream.
• Descartes' evil demon is a being "as clever and deceitful as he is powerful, who has directed his entire effort to misleading me".
• The five minute hypothesis (or omphalos hypothesis or Last Thursdayism) suggests that the world was created recently together with records and traces indicating a greater age.
• The simulated reality hypothesis or "Matrix hypothesis" suggest that everyone, or even the entire universe, might be inside a computer simulation or virtual reality.

History of Western skepticism

Ancient Greek skepticism

Pyrrho.

The Western tradition of systematic skepticism goes back at least as far as Pyrrho of Elis (b. circa 360 BCE). However, "The 5th century sophists develop forms of debate which are ancestors of skeptical argumentation. They take pride in arguing in a persuasive fashion for both sides of an issue." There were many disputes that could be found within the philosophical schools of his day, and according to a later account of his life by his student Timon of Phlius, Pyrrho extolled a way to become happy and tranquil.

"Whoever wants to live well (eudaimonia) must consider these three questions: First, how are pragmata (ethical matters, affairs, topics) by nature? Secondly, what attitude should we adopt towards them? Thirdly, what will be the outcome for those who have this attitude?" Pyrrho's answer is that "As for pragmata they are all adiaphora (undifferentiated by a logical differentia), astathmēta (unstable, unbalanced, not measurable), and anepikrita (unjudged, unfixed, undecidable). Therefore, neither our sense-perceptions nor our doxai (views, theories, beliefs) tell us the truth or lie; so we certainly should not rely on them. Rather, we should be adoxastous (without views), aklineis (uninclined toward this side or that), and akradantous (unwavering in our refusal to choose), saying about every single one that it no more is than it is not or it both is and is not or it neither is nor is not.

The main principle of Pyrrho's thought is expressed by the word acatalepsia, which connotes the ability to withhold assent from doctrines regarding the truth of things in their own nature; against every statement its contradiction may be advanced with equal justification.

Pyrrhonists are not "skeptics" in the modern, common sense of the term, meaning prone to disbelief. They had the goal of αταραξια (ataraxia - peace of mind), and pitted one dogma against another to undermine belief in dogmatic propositions. The idea was to produce in the student a state of indifference towards ideas about non-evident matters. Since no one can observe or otherwise experience causation, external world (its "externality"), ultimate purpose of the universe or life, justice, divinity, soul, etc., they declared no need to believe in such things. The Pyrrhonists pointed out that, despite claims that such notions were necessary, some people ignorant of them get by just fine before learning about them. They further noted that science does not require belief and that faith in intelligible realities is different from pragmatic convention for the sake of experiment. For each intuitive notion (e.g. the existence of an external world), the Pyrrhonists cited a contrary opinion to negate it. They added that consensus indicates neither truth nor even probability.

Pyrrho's thinking subsequently influenced Plato's Academy, creating the Academic skepticism of the New or Middle Academy, Arcesilaus (c. 315 – 241 BCE) and Carneades (c. 213–129 BCE) argued from Stoic premises that the Stoics were actually committed to denying the possibility of knowledge, but seemed to maintain nothing themselves, but Clitomachus, a student of Carneades, interpreted his teacher's philosophy as suggesting an early probabilistic account of knowledge. The Roman politician and philosopher, Cicero, also seems to have been a supporter of the probabilistic position attributed to the Middle Academy, even if the return to a more dogmatic orientation of that school was already beginning to take place.

Diogenes Laërtius lists ten modes of reasoning which Pyrrhonists thought justified their position:

1. Some things give animals pleasure which give other animals pain. What is useful to one animal is harmful to another.
2. Each human has a different assortment of preferences, abilities and interests.
3. Each sense gives a different impression of the same object.
4. There is no reason to think one is sane while others are insane—the opposite could be true.
5. Cultures disagree regarding beauty, truth, goodness, religion, life and justice.
6. There is no consistency in perception. (His examples were that the color purple will show different tints depending on the lighting, a person looks different between noon and sunset, and a very heavy rock on land is lighter when in water)
7. The senses can be shown to be deceptive. (From a distance, the square tower looks round and the sun looks small)
8. Things that strengthen in moderation will weaken when taken in excess, like wine and food.
9. When a thing is rare, it surprises people. When a thing is common, it does not surprise people.
10. Inter-relations among things are of course relative, and by themselves are unknowable. (e.g. to know 'parent' you must know 'child,' and to know 'child' you must know 'parent.' Neither can be known by itself.)

In the centuries to come, the words Academician and Pyrrhonist would often be used to mean generally skeptic, often ignoring historical changes and distinctions between denial of knowledge and avoidance of belief, between degree of belief and absolute belief, and between possibility and probability.

Sextus Empiricus

Sextus Empiricus

Sextus Empiricus (c. 200 CE), the main authority for Pyrrhonian skepticism, worked outside the Academy, which by his time had ceased to be a skeptical or probabilistic school, and argued in a different direction, incorporating aspects of empiricism into the basis for evaluating knowledge, but without the insistence on experience as the absolute standard of it. Sextus' empiricism was limited to the "absolute minimum" already mentioned — that there seem to be appearances. He developed this basic thought of Pyrrho's into lengthy arguments, most of them directed against Stoics and Epicureans, but also the Academic skeptics. The common anti-skeptical argument is that if one knows nothing, one cannot know that one knows nothing, and so may know something after all. It is worth noting that such an argument only succeeds against the complete denial of the possibility of knowledge. Considering dogmatic the claims both to know and not to know, Sextus and his followers claimed neither. Instead, despite the apparent conflict with the goal of ataraxia, they claimed to continue searching for something that might be knowable.

Empiricus, as the most systematic author of the works by Hellenistic sceptics which have survived, noted that there are at least ten modes of skepticism. These modes may be broken down into three categories: one may be skeptical of the subjective perceiver, of the objective world, and the relation between perceiver and the world. His arguments are as follows.

Subjectively, both the powers of the senses and of reasoning may vary among different people. And since knowledge is a product of one or the other, and since neither are reliable, knowledge would seem to be in trouble. For instance, a color-blind person sees the world quite differently from everyone else. Moreover, one cannot even give preference on the basis of the power of reason, i.e., by treating the rational animal as a carrier of greater knowledge than the irrational animal, since the irrational animal is still adept at navigating their environment, which suggests the ability to "know" about some aspects of the environment.

Secondly, the personality of the individual might also influence what they observe, since (it is argued) preferences are based on sense-impressions, differences in preferences can be attributed to differences in the way that people are affected by the object. (Empiricus:56)

Third, the perceptions of each individual sense seemingly have nothing in common with the other senses: i.e., the color "red" has little to do with the feeling of touching a red object. This is manifest when our senses "disagree" with each other: for example, a mirage presents certain visible features, but is not responsive to any other kind of sense. In that case, our other senses defeat the impressions of sight. But one may also be lacking enough powers of sense to understand the world in its entirety: if one had an extra sense, then one might know of things in a way that the present five senses are unable to advise us of. Given that our senses can be shown to be unreliable by appealing to other senses, and so our senses may be incomplete (relative to some more perfect sense that one lacks), then it follows that all of our senses may be unreliable. (Empiricus:58)

Fourth, our circumstances when one perceives anything may be either natural or unnatural, i.e., one may be either in a state of wakefulness or sleep. But it is entirely possible that things in the world really are exactly as they appear to be to those in unnatural states (i.e., if everything were an elaborate dream). (Empiricus:59)

One can have reasons for doubt that are based on the relationship between objective "facts" and subjective experience. The positions, distances, and places of objects would seem to affect how they are perceived by the person: for instance, the portico may appear tapered when viewed from one end, but symmetrical when viewed at the other; and these features are different. Because they are different features, to believe the object has both properties at the same time is to believe it has two contradictory properties. Since this is absurd, one must suspend judgment about what properties it possesses due to the contradictory experiences. (Empiricus:63)

One may also observe that the things one perceives are, in a sense, polluted by experience. Any given perception—say, of a chair—will always be perceived within some context or other (i.e., next to a table, on a mat, etc.) Since this is the case, one often only speaks of ideas as they occur in the context of the other things that are paired with it, and therefore, one can never know of the true nature of the thing, but only how it appears to us in context. (Empiricus: 64)

Along the same lines, the skeptic may insist that all things are relative, by arguing that:

1. Absolute appearances either differ from relative appearances, or they do not.
2. If absolutes do not differ from relatives, then they are themselves relative.
3. But if absolutes do differ from relatives, then they are relative, because all things that differ must differ from something; and to "differ" from something is to be relative to something. (Empiricus:67)

Finally, one has reason to disbelieve that one knows anything by looking at problems in understanding objects by themselves. Things, when taken individually, may appear to be very different from when they are in mass quantities: for instance, the shavings of a goat's horn are white when taken alone, yet the horn intact is black.

Augustine and skepticism

Augustine of Hippo

In 386 CE, Augustine published Contra Academicos (Against the Skeptics), which argued against claims that Academic Skeptics (266 BCE - 90 BCE) made:

• Objection from Error: Through logic, Augustine proves that Skepticism does not lead to happiness like the academic skeptics claim. His proof is summarized below.
  1. A wise man lives according to reason, and thus is able to be happy.
  2. One who is searching for knowledge but never finds it is in error.
  3. Imperfection objection: People in error are not happy, because being in error is an imperfection, and people cannot be happy with an imperfection.
  4. Conclusion: One who is still seeking knowledge cannot be happy.
• Error of Non-Assent: Augustine's proof that suspending belief does not fully prevent one from error. His proof is summarized below.
  1. Introduction of the error: Let P be true. If a person fails to believe P due to suspension of belief in order to avoid error, the person is also committing an error.
  2. The Anecdote of the Two Travelers: Travelers A and B are trying to reach the same destination. At a fork in the road, a poor shepherd tells them to go left. Traveler A immediately believes him and reaches the correct destination. Traveler B suspends belief, instead believing in the advice of a well-dressed townsman to go right, because his advice seems more persuasive. However, the townsman is actually a samardocus (con man) so Traveler B never reaches the correct destination.
  3. The Anecdote of the Adulterer: A man suspends belief that adultery is bad, and commits adultery with another man's wife because it is persuasive to him. Under Academic Skepticism, this man cannot be charged because he acted on what was persuasive to him without assenting belief.
  4. Conclusion: Suspending belief exposes individuals to an error as defined by the Academic Skeptics.

Skepticism's revival in the sixteenth century

Michel de Montaigne (1533–1592)

Michel de Montaigne

The most notable figure of the Skepticism revival in the 1500s, Montaigne wrote about his studies of Academic Skepticism and Pyrrhonism through his Essais.

His most notable writings on Skepticism occurred in an essay written mostly in 1575–1576, "Apologie de Raimond Sebond," when he was reading Sextus Empiricus and trying to translate Raimond Sebond's writing, including his proof of Christianity's natural existence. The reception to Montaigne's translations included some criticisms of Sebond's proof. Montaigne responded to some of them in Apologie, including a defense for Sebond's logic that is skeptical in nature and similar to Pyrrhonism. His refutation is as follows:

1. Critics claiming Sebond's arguments are weak show how egoistic humans believe that their logic is superior to others.
2. Many animals can be observed to be superior to humans in certain respects. To argue this point, Montaigne even writes about dogs who are logical and creates their own syllogisms to understand the world around them. This was an example used in Sextus Empiricus.
3. Since animals also have rationality, the over-glorification of man's mental capabilities is a trap—man's folly. One man's reason cannot be assuredly better than another's as a result.
4. Ignorance is even recommend by religion so that an individual can reach faith through obediently following divine instructions to learn, not by one's logic.

Marin Mersenne (1588–1648)

Marin Mersenne

Marin Mersenne was an author, a mathematician, a scientist, and a philosopher. He wrote in defense of science and Christianity against atheists and Pyrrhonists before retiring to encourage development of science and the "new philosophy," which includes philosophers like Gassendi, Descartes, Galileo, and Hobbes. A major work of his in relation to Skepticism is La Verité des Sciences, in which he argues that although we may not be able to know the true nature of things, we can still formulate certain laws and rules for sense-perceptions through science.

Additionally, he points out that we do not doubt everything because:

• Humans do agree about some things, for example, an ant is smaller than an elephant
• There are natural laws governing our sense-perceptions, such as optics, which allow us to eliminate inaccuracies
• Man created tools such as rulers and scales to measure things and eliminate doubts such as bent oars, pigeons’ necks, and round towers.

A Pyrrhonist might refute these points by saying that senses deceive, and thus knowledge turns into infinite regress or circular logic. Thus Mersenne argues that this cannot be the case, since commonly agreed upon rules of thumb can be hypothesized and tested over time to ensure that they continue to hold.

Furthermore, if everything can be doubted, the doubt can also be doubted, so on and so forth. Thus, according to Mersenne, something has to be true. Finally, Mersenne writes about all the mathematical, physical, and other scientific knowledge that is true by repeated testing, and has practical use value. Notably, Mersenne was one of the few philosophers who accepted Hobbes' radical ideology—he saw it as a new science of man.

Skepticism in the seventeenth century

Thomas Hobbes

Thomas Hobbes (1588–1679)

During his long stay in Paris, Thomas Hobbes was actively involved in the circle of major skeptics like Gassendi and Mersenne who focus on the study of skepticism and epistemology. Unlike his fellow skeptic friends, Hobbes never treated skepticism as a main topic for discussion in his works. Nonetheless, Hobbes was still labeled as a religious skeptic by his contemporaries for raising doubts about Mosaic authorship of the Pentateuch and his political and psychological explanation of the religions. Although Hobbes himself did not go further to challenge other religious principles, his suspicion for the Mosaic authorship did significant damage to the religious traditions and paved the way for later religious skeptics like Spinoza and Isaac La Peyrère to further question some of the fundamental beliefs of the Judeo-Christian religious system. Hobbes' answer to skepticism and epistemology was innovatively political: he believed that moral knowledge and religious knowledge were in their nature relative, and there was no absolute standard of truth governing them. As a result, it was out of political reasons that certain truth standards about religions and ethics were devised and established in order to form functioning government and stable society.

Baruch Spinoza

Baruch Spinoza and religious skepticism (1632–1677)

Baruch Spinoza was among the first European philosophers who were religious skeptics. He was quite familiar with the philosophy of Descartes and unprecedentedly extended the application of the Cartesian method to the religious context by analyzing religious texts with it. Spinoza sought to dispute the knowledge-claims of the Judeo-Christian-Islamic religious system by examining its two foundations: the Scripture and the Miracles. He claimed that all Cartesian knowledge, or the rational knowledge should be accessible to the entire population. Therefore, the Scriptures, aside from those by Jesus, should not be considered the secret knowledge attained from God but just the imagination of the prophets. The Scriptures, as a result of this claim, could not serve as a base for knowledge and were reduced to simple ancient historical texts. Moreover, Spinoza also rejected the possibility for the Miracles by simply asserting that people only considered them miraculous due to their lack of understanding of the nature. By rejecting the validity of the Scriptures and the Miracles, Spinoza demolished the foundation for religious knowledge-claim and established his understanding of the Cartesian knowledge as the sole authority of knowledge-claims. Despite being deeply-skeptical of the religions, Spinoza was in fact exceedingly anti-skeptical towards reason and rationality. He steadfastly confirmed the legitimacy of reason by associating it with the acknowledgement of God, and thereby skepticism with the rational approach to knowledge was not due to problems with the rational knowledge but from the fundamental lack of understanding of God. Spinoza's religious skepticism and anti-skepticism with reason thus helped him transform epistemology by separating the theological knowledge-claims and the rational knowledge-claims.

Pierre Bayle (1647–1706)

Pierre Bayle by Louis Ferdinand Elle

Pierre Bayle was a French philosopher in the late 17th century that was described by Richard Popkin to be a "supersceptic" who carried out the sceptic tradition to the extreme. Bayle was born in a Calvinist family in Carla-Bayle, and during the early stage of his life, he converted into Catholicism before returning to Calvinism. This conversion between religions caused him to leave France for the more religiously tolerant Holland where he stayed and worked for the rest of his life.

Bayle believed that truth cannot be obtained through reason and that all human endeavor to acquire absolute knowledge would inevitably lead to failure. Bayle's main approach was highly skeptical and destructive: he sought to examine and analyze all existing theories in all fields of human knowledge in order to show the faults in their reasoning and thus the absurdity of the theories themselves. In his magnum opus, Dictionnaire Historique et Critique (Historical and Critical Dictionary), Bayle painstakingly identified the logical flaws in several works throughout the history in order to emphasize the absolute futility of rationality. Bayle's complete nullification of reason led him to conclude that faith is the final and only way to truth.

Bayle's real intention behind his extremely destructive works remained controversial. Some described him to be a Fideist, while others speculated him to be a secret Atheist. However, no matter what his original intention was, Bayle did cast significant influence on the upcoming Age of Enlightenment with his destruction of some of the most essential theological ideas and his justification of religious tolerance Atheism in his works.

Kant's skepticism and its influence on German philosophy

Kant

Immanuel Kant (1724–1804) tried to provide a ground for empirical science against David Hume's skeptical treatment of the notion of cause and effect. Hume (1711–1776) argued that for the notion of cause and effect no analysis is possible which is also acceptable to the empiricist program primarily outlined by John Locke (1632–1704). But, Kant's attempt to give a ground to knowledge in the empirical sciences at the same time cut off the possibility of knowledge of any other knowledge, especially what Kant called "metaphysical knowledge". So, for Kant, empirical science was legitimate, but metaphysics and philosophy was mostly illegitimate. The most important exception to this demarcation of the legitimate from the illegitimate was ethics, the principles of which Kant argued can be known by pure reason without appeal to the principles required for empirical knowledge. Thus, with respect to metaphysics and philosophy in general (ethics being the exception), Kant was a skeptic. This skepticism as well as the explicit skepticism of G. E. Schulze gave rise to a robust discussion of skepticism in classical German philosophy, especially by Hegel. Kant's idea was that the real world (the noumenon or thing-in-itself) was inaccessible to human reason (though the empirical world of nature can be known to human understanding) and therefore we can never know anything about the ultimate reality of the world. Hegel argued against Kant that although Kant was right that using what Hegel called "finite" concepts of "the understanding" precluded knowledge of reality, we were not constrained to use only "finite" concepts and could actually acquire knowledge of reality using "infinite concepts" that arise from self-consciousness.

Emerging discussion after the death of Richard Popkin

Because Richard Popkin was one of the founding fathers of study in this area, the account of the history of Skepticism in his books are accepted as the standard. However, recent scholars have been suggesting an addition to Popkin's account. Instead of centering the history of Skepticism around specific figures who wrote key skeptical works, Skepticism is proposed to be a continuous engagement with works by ancients like Sextus Empiricus to modern thinkers like Hume. The engagement with previous works were probably due to unwanted doubts about accepted episteme instead of purely due to classical writings becoming available at any specific time.

History of skepticism in non-Western philosophy

Ancient Indian skepticism

Indian skepticism towards dogmatic statements is illustrated by the famous tale of the Blind men and an elephant, common in Buddhism and Jainism.

Ajñana

Ajñana (literally 'non-knowledge') were the skeptical school of ancient Indian philosophy. It was a śramaṇa movement and a major rival of early Buddhism and Jainism. They have been recorded in Buddhist and Jain texts. They held that it was impossible to obtain knowledge of metaphysical nature or ascertain the truth value of philosophical propositions; and even if knowledge was possible, it was useless and disadvantageous for final salvation.

Buddhism

The historical Buddha asserted certain doctrines as true, such as the possibility of nirvana, however he also upheld a form of skepticism with regards to certain questions which he left "un-expounded" (avyākata) and some he saw as "incomprehensible" (acinteyya). Because the Buddha saw these questions (which tend to be of metaphysical topics) as unhelpful on the path and merely leading to confusion and "a thicket of views", he promoted suspension of judgment towards them. This allowed him to carve out an epistemic middle way between what he saw as the extremes of claiming absolute objectivity (associated with the claims to omniscience of the Jain Mahavira) and extreme skepticism (associated with the Ajñana thinker Sanjaya Belatthiputta).

Later Buddhist Philosophy remained highly skeptical of Indian metaphysical arguments. The Buddhist philosopher Nagarjuna in particular has been seen as the founder of the Madhyamaka school, which has been in turn compared with Greek Skepticism. Nagarjuna's statement that he has "no thesis" (pratijña) has parallels in the statements of Sextus Empiricus of having "no position". Nagarjuna famously opens his magnum opus, the Mulamadhyamakakarika, with the statement that the Buddha claimed that true happiness was found through dispelling 'vain thinking' (prapañca, also "conceptual proliferation").

According to Richard P. Hayes, the Buddhist philosopher Dignaga is also a kind of skeptic, which is in line with most early Buddhist philosophy. Hayes writes:

...in both early Buddhism and in the Skeptics one can find the view put forward that man's pursuit of happiness, the highest good, is obstructed by his tenacity in holding ungrounded and unnecessary opinions about all manner of things. Much of Buddhist philosophy, I shall argue, can be seen as an attempt to break this habit of holding on to opinions.^[35]

Scholars like Adrian Kuzminski have argued that Pyrrho of Elis (ca. 365–270) might have been influenced by Indian Buddhists during his journey with Alexander the Great.

Cārvāka philosophy

The Cārvāka (Sanskrit: चार्वाक) school of materialism, also known as Lokāyata, is a distinct branch of Indian philosophy. The school is named after Cārvāka, author of the Bārhaspatya-sūtras and was founded in approximately 500 BC. Cārvāka is classified as a "heterodox" (nāstika) system, characterized as a materialistic and atheistic school of thought. This school was also known for being strongly skeptical of the claims of Indian religions, such as reincarnation and karma.

Jainism

While Jain philosophy claims that is it possible to achieve omniscience, absolute knowledge (Kevala Jnana), at the moment of enlightenment, their theory of anekāntavāda or 'many sided-ness', also known as the principle of relative pluralism, allows for a practical form of skeptical thought regarding philosophical and religious doctrines (for un-enlightened beings, not all-knowing arihants).

According to this theory, the truth or the reality is perceived differently from different points of view, and that no single point of view is the complete truth. Jain doctrine states that, an object has infinite modes of existence and qualities and, as such, they cannot be completely perceived in all its aspects and manifestations, due to inherent limitations of the humans. Anekāntavāda is literally the doctrine of non-onesidedness or manifoldness; it is often translated as "non-absolutism". Syādvāda is the theory of conditioned predication which provides an expression to anekānta by recommending that epithet “Syād” be attached to every expression. Syādvāda is not only an extension of Anekānta ontology, but a separate system of logic capable of standing on its own force. As reality is complex, no single proposition can express the nature of reality fully. Thus the term “syāt” should be prefixed before each proposition giving it a conditional point of view and thus removing any dogmatism in the statement. For Jains, fully enlightened beings are able to see reality from all sides and thus have ultimate knowledge of all things. This idea of omniscience was criticized by Buddhists such as Dharmakirti.

Ancient Chinese philosophy

A Painting of Zhuangzi and his Butterfly Dream

Zhuang Zhou (c. 369 – c. 286 BC)

Zhuang Zhou (庄子，"Master Zhuang") was a famous ancient Chinese Taoism philosopher during the Hundred Schools of Thought period. Zhuang Zhou demonstrated his skeptical thinking through several anecdotes in the preeminent work Zhuangzi that was attributed to him:

• "The Debate on the Joy of Fish" (知鱼之乐) : In this anecdote, Zhuang Zhou argued with his fellow philosopher Hui Shi on if they knew the fish in the pond was happy or not, and Zhuang Zhou said the famous sentence that "You are not I. How do you know that I do not know that the fish are happy?"  ( Autumn Floods 秋水篇, Zhuangzi)
• "The Butterfly of the Dream"(周公梦蝶) : The paradox of "Butterfly Dream" described Zhuang Zhou's confusion after dreaming himself to be a butterfly: "But he didn't know if he was Zhuang Zhou who had dreamt he was a butterfly, or a butterfly dreaming that he was Zhuang Zhou."  (Discussion on Making All Things Equal 齐物篇, Zhuangzi)

Through these anecdotes in Zhuangzi, Zhuang Zhou indicated his belief in the limitation of language and human communication and the inaccessibility of universal truth which established himself as an skeptic. But Zhuang Zhou was by no means a radical skeptic, since he only applied skeptical methods partially in some of his arguments to demonstrate his Taoism beliefs while adopting these Taoism beliefs in a dogmatic fashion.

Wang Chong (27 – c. 100 AD)

Wang Chong (王充) was the leading figure of the skeptic branch of the Confucianism school in China during the first century AD. He introduced a method of rational critique and applied it to the wide-spread dogmatism thinking of his age like phenomenology (the main contemporary Confucianism ideology that linked all natural phenomena with human ethics), state-led cults, and popular superstition. His own philosophy incorporated both Taoism and Confucianism thinkings, and it was based on a secular, rational practice of developing hypotheses based on natural events to explain the universe which exemplified a form of naturalism that resembled the philosophical idea of Epicureans like Lucretius.

Medieval Arabic philosophy

The Incoherence of the Philosophers, written by the scholar Al-Ghazali (1058–1111), marks a major turn in Islamic epistemology. His encounter with skepticism led Ghazali to embrace a form of theological occasionalism, or the belief that all causal events and interactions are not the product of material conjunctions but rather the immediate and present will of God. While he himself was a critic of the philosophers, Ghazali was a master in the art of philosophy and had immensely studied the field. After such a long education in philosophy, as well as a long process of reflection, he had criticized the philosophical method.

In the autobiography Ghazali wrote towards the end of his life, The Deliverance From Error (Al-munqidh min al-ḍalāl), Ghazali recounts how, once a crisis of epistemological skepticism was resolved by "a light which God Most High cast into my breast...the key to most knowledge," he studied and mastered the arguments of Kalam, Islamic philosophy, and Ismailism. Though appreciating what was valid in the first two of these, at least, he determined that all three approaches were inadequate and found ultimate value only in the mystical experience and spiritual insight he attained as a result of following Sufi practices. William James, in Varieties of Religious Experience, considered the autobiography an important document for "the purely literary student who would like to become acquainted with the inwardness of religions other than the Christian", comparing it to recorded personal religious confessions and autobiographical literature in the Christian tradition.

Aztec philosophy

Recordings of Aztec philosophy suggest that the elite classes believed in an essentially panentheistic worldview, in which teotl represents an unified, underlying universal force. Human beings cannot truly perceive teotl due to its chaotic, constantly changing nature, just the "masks"/facets it is manifested as.

Knowledge

From Wikipedia, the free encyclopedia

Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts, information, descriptions, or skills, which is acquired through experience or education by perceiving, discovering, or learning.

Knowledge can refer to a theoretical or practical understanding of a subject. It can be implicit (as with practical skill or expertise) or explicit (as with the theoretical understanding of a subject); it can be more or less formal or systematic. In philosophy, the study of knowledge is called epistemology; the philosopher Plato famously defined knowledge as "justified true belief", though this definition is now thought by some analytic philosophers to be problematic because of the Gettier problems while others defend the platonic definition. However, several definitions of knowledge and theories to explain it exist.

Knowledge acquisition involves complex cognitive processes: perception, communication, and reasoning; while knowledge is also said to be related to the capacity of acknowledgement in human beings.

Theories of knowledge

Robert Reid, Knowledge (1896). Thomas Jefferson Building, Washington, D.C.

The eventual demarcation of philosophy from science was made possible by the notion that philosophy's core was "theory of knowledge," a theory distinct from the sciences because it was their foundation... Without this idea of a "theory of knowledge," it is hard to imagine what "philosophy" could have been in the age of modern science.

— Richard Rorty, Philosophy and the Mirror of Nature

The definition of knowledge is a matter of ongoing debate among philosophers in the field of epistemology. The classical definition, described but not ultimately endorsed by Plato, specifies that a statement must meet three criteria in order to be considered knowledge: it must be justified, true, and believed. Some claim that these conditions are not sufficient, as Gettier case examples allegedly demonstrate. There are a number of alternatives proposed, including Robert Nozick's arguments for a requirement that knowledge 'tracks the truth' and Simon Blackburn's additional requirement that we do not want to say that those who meet any of these conditions 'through a defect, flaw, or failure' have knowledge. Richard Kirkham suggests that our definition of knowledge requires that the evidence for the belief necessitates its truth.

In contrast to this approach, Ludwig Wittgenstein observed, following Moore's paradox, that one can say "He believes it, but it isn't so," but not "He knows it, but it isn't so." He goes on to argue that these do not correspond to distinct mental states, but rather to distinct ways of talking about conviction. What is different here is not the mental state of the speaker, but the activity in which they are engaged. For example, on this account, to know that the kettle is boiling is not to be in a particular state of mind, but to perform a particular task with the statement that the kettle is boiling. Wittgenstein sought to bypass the difficulty of definition by looking to the way "knowledge" is used in natural languages. He saw knowledge as a case of a family resemblance. Following this idea, "knowledge" has been reconstructed as a cluster concept that points out relevant features but that is not adequately captured by any definition.

Communicating knowledge

Los portadores de la antorcha (The Torch-Bearers) – Sculpture by Anna Hyatt Huntington symbolizing the transmission of knowledge from one generation to the next (Ciudad Universitaria, Madrid, Spain)

Symbolic representations can be used to indicate meaning and can be thought of as a dynamic process. Hence the transfer of the symbolic representation can be viewed as one ascription process whereby knowledge can be transferred. Other forms of communication include observation and imitation, verbal exchange, and audio and video recordings. Philosophers of language and semioticians construct and analyze theories of knowledge transfer or communication.
While many would agree that one of the most universal and significant tools for the transfer of knowledge is writing and reading (of many kinds), argument over the usefulness of the written word exists nonetheless, with some scholars skeptical of its impact on societies. In his collection of essays Technopoly, Neil Postman demonstrates the argument against the use of writing through an excerpt from Plato's work Phaedrus (Postman, Neil (1992) Technopoly, Vintage, New York, pp 73). In this excerpt, the scholar Socrates recounts the story of Thamus, the Egyptian king and Theuth the inventor of the written word. In this story, Theuth presents his new invention "writing" to King Thamus, telling Thamus that his new invention "will improve both the wisdom and memory of the Egyptians" (Postman, Neil (1992) Technopoly, Vintage, New York, p. 74). King Thamus is skeptical of this new invention and rejects it as a tool of recollection rather than retained knowledge. He argues that the written word will infect the Egyptian people with fake knowledge as they will be able to attain facts and stories from an external source and will no longer be forced to mentally retain large quantities of knowledge themselves (Postman, Neil (1992) Technopoly, Vintage, New York, p. 74).

Classical early modern theories of knowledge, especially those advancing the influential empiricism of the philosopher John Locke, were based implicitly or explicitly on a model of the mind which likened ideas to words. This analogy between language and thought laid the foundation for a graphic conception of knowledge in which the mind was treated as a table, a container of content, that had to be stocked with facts reduced to letters, numbers or symbols. This created a situation in which the spatial alignment of words on the page carried great cognitive weight, so much so that educators paid very close attention to the visual structure of information on the page and in notebooks.

Major libraries today can have millions of books of knowledge (in addition to works of fiction). It is only recently that audio and video technology for recording knowledge have become available and the use of these still requires replay equipment and electricity. Verbal teaching and handing down of knowledge is limited to those who would have contact with the transmitter or someone who could interpret written work. Writing is still the most available and most universal of all forms of recording and transmitting knowledge. It stands unchallenged as mankind's primary technology of knowledge transfer down through the ages and to all cultures and languages of the world.

Situated knowledge

"Situated knowledges" redirects here. For the Donna Haraway essay, see Situated Knowledges.

Situated knowledge is knowledge specific to a particular situation. It is a term coined by Donna Haraway as an extension of the feminist approaches of "successor science" suggested by Sandra Harding, one which "offers a more adequate, richer, better account of a world, in order to live in it well and in critical, reflexive relation to our own as well as others' practices of domination and the unequal parts of privilege and oppression that makes up all positions." This situation partially transforms science into a narrative, which Arturo Escobar explains as, "neither fictions nor supposed facts." This narrative of situation is historical textures woven of fact and fiction, and as Escobar explains further, "even the most neutral scientific domains are narratives in this sense," insisting that rather than a purpose dismissing science as a trivial matter of contingency, "it is to treat (this narrative) in the most serious way, without succumbing to its mystification as 'the truth' or to the ironic skepticism common to many critiques."

Haraway's argument stems from the limitations of the human perception, as well as the overemphasis of the sense of vision in science. According to Haraway, vision in science has been, "used to signify a leap out of the marked body and into a conquering gaze from nowhere." This is the "gaze that mythically inscribes all the marked bodies, that makes the unmarked category claim the power to see and not be seen, to represent while escaping representation." This causes a limitation of views in the position of science itself as a potential player in the creation of knowledge, resulting in a position of "modest witness". This is what Haraway terms a "god trick", or the aforementioned representation while escaping representation. In order to avoid this, "Haraway perpetuates a tradition of thought which emphasizes the importance of the subject in terms of both ethical and political accountability".

Some methods of generating knowledge, such as trial and error, or learning from experience, tend to create highly situational knowledge. One of the main attributes of the scientific method is that the theories it generates are much less situational than knowledge gained by other methods. Situational knowledge is often embedded in language, culture, or traditions. This integration of situational knowledge is an allusion to the community, and its attempts at collecting subjective perspectives into an embodiment "of views from somewhere."

Knowledge generated through experience is called knowledge "a posteriori", meaning afterwards. The pure existence of a term like "a posteriori" means this also has a counterpart. In this case, that is knowledge "a priori", meaning before. The knowledge prior to any experience means that there are certain "assumptions" that one takes for granted. For example, if you are being told about a chair, it is clear to you that the chair is in space, that it is 3D. This knowledge is not knowledge that one can "forget", even someone suffering from amnesia experiences the world in 3D.

Even though Haraway's arguments are largely based on feminist studies, this idea of different worlds, as well as the skeptic stance of situated knowledge is present in the main arguments of post-structuralism. Fundamentally, both argue the contingency of knowledge on the presence of history; power, and geography, as well as the rejection of universal rules or laws or elementary structures; and the idea of power as an inherited trait of objectification.

Partial knowledge

The parable of Blind men and an elephant suggests that people tend to project their partial experiences as the whole truth

One discipline of epistemology focuses on partial knowledge. In most cases, it is not possible to understand an information domain exhaustively; our knowledge is always incomplete or partial. Most real problems have to be solved by taking advantage of a partial understanding of the problem context and problem data, unlike the typical math problems one might solve at school, where all data is given and one is given a complete understanding of formulas necessary to solve them.

This idea is also present in the concept of bounded rationality which assumes that in real life situations people often have a limited amount of information and make decisions accordingly.
Intuition is the ability to acquire partial knowledge without inference or the use of reason. An individual may "know" about a situation and be unable to explain the process that led to their knowledge.

Scientific knowledge

Sir Francis Bacon, "Knowledge is Power"

The development of the scientific method has made a significant contribution to how knowledge of the physical world and its phenomena is acquired. To be termed scientific, a method of inquiry must be based on gathering observable and measurable evidence subject to specific principles of reasoning and experimentation. The scientific method consists of the collection of data through observation and experimentation, and the formulation and testing of hypotheses. Science, and the nature of scientific knowledge have also become the subject of Philosophy. As science itself has developed, scientific knowledge now includes a broader usage in the soft sciences such as biology and the social sciences – discussed elsewhere as meta-epistemology, or genetic epistemology, and to some extent related to "theory of cognitive development". Note that "epistemology" is the study of knowledge and how it is acquired. Science is "the process used everyday to logically complete thoughts through inference of facts determined by calculated experiments." Sir Francis Bacon was critical in the historical development of the scientific method; his works established and popularized an inductive methodology for scientific inquiry. His famous aphorism, "knowledge is power", is found in the Meditations Sacrae (1597).

Until recent times, at least in the Western tradition, it was simply taken for granted that knowledge was something possessed only by humans – and probably adult humans at that. Sometimes the notion might stretch to Society-as-such, as in (e. g.) "the knowledge possessed by the Coptic culture" (as opposed to its individual members), but that was not assured either. Nor was it usual to consider unconscious knowledge in any systematic way until this approach was popularized by Freud.

Other biological domains where "knowledge" might be said to reside, include: (iii) the immune system, and (iv) in the DNA of the genetic code. See the list of four "epistemological domains": Popper, (1975); and Traill (2008: Table S, p. 31) – also references by both to Niels Jerne.

Such considerations seem to call for a separate definition of "knowledge" to cover the biological systems. For biologists, knowledge must be usefully available to the system, though that system need not be conscious. Thus the criteria seem to be:

• The system should apparently be dynamic and self-organizing (unlike a mere book on its own).
• The knowledge must constitute some sort of representation of "the outside world", or ways of dealing with it (directly or indirectly).
• Some way must exist for the system to access this information quickly enough for it to be useful.

Scientific knowledge may not involve a claim to certainty, maintaining skepticism means that a scientist will never be absolutely certain when they are correct and when they are not. It is thus an irony of proper scientific method that one must doubt even when correct, in the hopes that this practice will lead to greater convergence on the truth in general.

Religious meaning of knowledge

In many expressions of Christianity, such as Catholicism and Anglicanism, knowledge is one of the seven gifts of the Holy Spirit.

The Old Testament's tree of the knowledge of good and evil contained the knowledge that separated Man from God: "And the LORD God said, Behold, the man is become as one of us, to know good and evil..." (Genesis 3:22)

In Gnosticism, divine knowledge or gnosis is hoped to be attained.

विद्या दान (Vidya Daan) i.e. knowledge sharing is a major part of Daan, a tenet of all Dharmic Religions. Hindu Scriptures present two kinds of knowledge, Paroksh Gyan and Prataksh Gyan. Paroksh Gyan (also spelled Paroksha-Jnana) is secondhand knowledge: knowledge obtained from books, hearsay, etc. Prataksh Gyan (also spelled Prataksha-Jnana) is the knowledge borne of direct experience, i.e., knowledge that one discovers for oneself. Jnana yoga ("path of knowledge") is one of three main types of yoga expounded by Krishna in the Bhagavad Gita. (It is compared and contrasted with Bhakti Yoga and Karma yoga.)

In Islam, knowledge (Arabic: علم, ʿilm) is given great significance. "The Knowing" (al-ʿAlīm) is one of the 99 names reflecting distinct attributes of God. The Qur'an asserts that knowledge comes from God (2:239) and various hadith encourage the acquisition of knowledge. Muhammad is reported to have said "Seek knowledge from the cradle to the grave" and "Verily the men of knowledge are the inheritors of the prophets". Islamic scholars, theologians and jurists are often given the title alim, meaning "knowledgeble".

In Jewish tradition, knowledge (Hebrew: דעת da'ath) is considered one of the most valuable traits a person can acquire. Observant Jews recite three times a day in the Amidah "Favor us with knowledge, understanding and discretion that come from you. Exalted are you, Existent-One, the gracious giver of knowledge." The Tanakh states, "A wise man gains power, and a man of knowledge maintains power", and "knowledge is chosen above gold".

As a measure of religiosity in sociology of religion

According to the sociologist Mervin F. Verbit, knowledge may be understood as one of the key components of religiosity. Religious knowledge itself may be broken down into four dimensions:

• content
• frequency
• intensity
• centrality

The content of one's religious knowledge may vary from person to person, as will the degree to which it may occupy the person's mind (frequency), the intensity of the knowledge, and the centrality of the information (in that religious tradition, or to that individual).

Biosphere

From Wikipedia, the free encyclopedia

A false-color composite of global oceanic and terrestrial photoautotroph abundance, from September 2001 to August 2017. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.

 

The biosphere (from Greek βίος bíos "life" and σφαῖρα sphaira "sphere") also known as the ecosphere (from Greek οἶκος oîkos "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be termed the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. By the most general biophysiological definition, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, geosphere, hydrosphere, and atmosphere. The biosphere is postulated to have evolved, beginning with a process of biopoiesis (life created naturally from non-living matter, such as simple organic compounds) or biogenesis (life created from living matter), at least some 3.5 billion years ago.

In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and potentially ones on other planets or moons.

Origin and use of the term

A beach scene on Earth, simultaneously showing the lithosphere (ground), hydrosphere (ocean) and atmosphere (air)

The term "biosphere" was coined by geologist Eduard Suess in 1875, which he defined as the place on Earth's surface where life dwells.

While the concept has a geological origin, it is an indication of the effect of both Charles Darwin and Matthew F. Maury on the Earth sciences. The biosphere's ecological context comes from the 1920s (see Vladimir I. Vernadsky), preceding the 1935 introduction of the term "ecosystem" by Sir Arthur Tansley (see ecology history). Vernadsky defined ecology as the science of the biosphere. It is an interdisciplinary concept for integrating astronomy, geophysics, meteorology, biogeography, evolution, geology, geochemistry, hydrology and, generally speaking, all life and Earth sciences.

Narrow definition

Geochemists define the biosphere as being the total sum of living organisms (the "biomass" or "biota" as referred to by biologists and ecologists). In this sense, the biosphere is but one of four separate components of the geochemical model, the other three being geosphere, hydrosphere, and atmosphere. When these four component spheres are combined into one system, it is known as the Ecosphere. This term was coined during the 1960s and encompasses both biological and physical components of the planet.

The Second International Conference on Closed Life Systems defined biospherics as the science and technology of analogs and models of Earth's biosphere; i.e., artificial Earth-like biospheres. Others may include the creation of artificial non-Earth biospheres—for example, human-centered biospheres or a native Martian biosphere—as part of the topic of biospherics.

Earth's biosphere

Age

Stromatolite fossil estimated at 3.2–3.6 billion years old

The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia. More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. In 2017, putative fossilized microorganisms (or microfossils) were announced to have been discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth ... then it could be common in the universe."

Extent

Rüppell's vulture

 

Xenophyophore, a barophilic organism, from the Galapagos Rift.

Every part of the planet, from the polar ice caps to the equator, features life of some kind. Recent advances in microbiology have demonstrated that microbes live deep beneath the Earth's terrestrial surface, and that the total mass of microbial life in so-called "uninhabitable zones" may, in biomass, exceed all animal and plant life on the surface. The actual thickness of the biosphere on earth is difficult to measure. Birds typically fly at altitudes as high as 1,800 m (5,900 ft; 1.1 mi) and fish live as much as 8,372 m (27,467 ft; 5.202 mi) underwater in the Puerto Rico Trench.

There are more extreme examples for life on the planet: Rüppell's vulture has been found at altitudes of 11,300 m (37,100 ft; 7.0 mi); bar-headed geese migrate at altitudes of at least 8,300 m (27,200 ft; 5.2 mi); yaks live at elevations as high as 5,400 m (17,700 ft; 3.4 mi) above sea level; mountain goats live up to 3,050 m (10,010 ft; 1.90 mi). Herbivorous animals at these elevations depend on lichens, grasses, and herbs.

Life forms live in every part of the Earth's biosphere, including soil, hot springs, inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere. Microorganisms, under certain test conditions, have been observed to survive the vacuum of outer space. The total amount of soil and subsurface bacterial carbon is estimated as 5 × 10¹⁷ g, or the "weight of the United Kingdom". The mass of prokaryote microorganisms—which includes bacteria and archaea, but not the nucleated eukaryote microorganisms—may be as much as 0.8 trillion tons of carbon (of the total biosphere mass, estimated at between 1 and 4 trillion tons). Barophilic marine microbes have been found at more than a depth of 10,000 m (33,000 ft; 6.2 mi) in the Mariana Trench, the deepest spot in the Earth's oceans. In fact, single-celled life forms have been found in the deepest part of the Mariana Trench, by the Challenger Deep, at depths of 11,034 m (36,201 ft; 6.856 mi). Other researchers reported related studies that microorganisms thrive inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of the northwestern United States, as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. Culturable thermophilic microbes have been extracted from cores drilled more than 5,000 m (16,000 ft; 3.1 mi) into the Earth's crust in Sweden, from rocks between 65–75 °C (149–167 °F). Temperature increases with increasing depth into the Earth's crust. The rate at which the temperature increases depends on many factors, including type of crust (continental vs. oceanic), rock type, geographic location, etc. The greatest known temperature at which microbial life can exist is 122 °C (252 °F) (Methanopyrus kandleri Strain 116), and it is likely that the limit of life in the "deep biosphere" is defined by temperature rather than absolute depth. On 20 August 2014, scientists confirmed the existence of microorganisms living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. According to one researcher, "You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."

Our biosphere is divided into a number of biomes, inhabited by fairly similar flora and fauna. On land, biomes are separated primarily by latitude. Terrestrial biomes lying within the Arctic and Antarctic Circles are relatively barren of plant and animal life, while most of the more populous biomes lie near the equator.

Annual variation

 

On land, vegetation appears on a scale from brown (low vegetation) to dark green (lots of vegetation); at the ocean surface, phytoplankton are indicated on a scale from purple (low) to yellow (high). This visualization was created with data from satellites including SeaWiFS, and instruments including the NASA/NOAA Visible Infrared Imaging Radiometer Suite and the Moderate Resolution Imaging Spectroradiometer.

Artificial biospheres

Biosphere 2 in Arizona.

Experimental biospheres, also called closed ecological systems, have been created to study ecosystems and the potential for supporting life outside the earth. These include spacecraft and the following terrestrial laboratories:

• Biosphere 2 in Arizona, United States, 3.15 acres (13,000 m²).
• BIOS-1, BIOS-2 and BIOS-3 at the Institute of Biophysics in Krasnoyarsk, Siberia, in what was then the Soviet Union.
• Biosphere J (CEEF, Closed Ecology Experiment Facilities), an experiment in Japan.
• Micro-Ecological Life Support System Alternative (MELiSSA) at Universitat Autònoma de Barcelona

Extraterrestrial biospheres

No biospheres have been detected beyond the Earth; therefore, the existence of extraterrestrial biospheres remains hypothetical. The rare Earth hypothesis suggests they should be very rare, save ones composed of microbial life only. On the other hand, Earth analogs may be quite numerous, at least in the Milky Way galaxy, given the large number of planets. Three of the planets discovered orbiting TRAPPIST-1 could possibly contain biospheres. Given limited understanding of abiogenesis, it is currently unknown what percentage of these planets actually develop biospheres.

Based on observations by the Kepler Space Telescope team, it has been calculated that provided the probability of abiogenesis is higher than 1 to 1000, the closest alien biosphere should be within 100 light-years from the Earth.

It is also possible that artificial biospheres will be created during the future, for example on Mars. The process of creating an uncontained system that mimics the function of Earth's biosphere is called terraforming.