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Saturday, March 1, 2025

Growth of photovoltaics

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Growth_of_photovoltaics
Benefitting from favorable policies and declining costs of modules, photovoltaic solar installation has grown consistently. In 2023, China added 60% of the world's new capacity.

Between 1992 and 2023, the worldwide usage of photovoltaics (PV) increased exponentially. During this period, it evolved from a niche market of small-scale applications to a mainstream electricity source. From 2016-2022 it has seen an annual capacity and production growth rate of around 26%- doubling approximately every three years.

When solar PV systems were first recognized as a promising renewable energy technology, subsidy programs, such as feed-in tariffs, were implemented by a number of governments in order to provide economic incentives for investments. For several years, growth was mainly driven by Japan and pioneering European countries. As a consequence, cost of solar declined significantly due to experience curve effects like improvements in technology and economies of scale. Several national programs were instrumental in increasing PV deployment, such as the Energiewende in Germany, the Million Solar Roofs project in the United States, and China's 2011 five-year-plan for energy production. Since then, deployment of photovoltaics has gained momentum on a worldwide scale, increasingly competing with conventional energy sources. In the early 21st century a market for utility-scale plants emerged to complement rooftop and other distributed applications. By 2015, some 30 countries had reached grid parity.

Since the 1950s, when the first solar cells were commercially manufactured, there has been a succession of countries leading the world as the largest producer of electricity from solar photovoltaics. First it was the United States, then Japan, followed by Germany, and currently China.

By the end of 2022, the global cumulative installed PV capacity reached about 1,185 gigawatts (GW), supplying over 6% of global electricity demand, up from about 3% in 2019. In 2022, solar PV contributed over 10% of the annual domestic consumption of electricity in nine countries, with Spain, Greece and Chile over 17%.

Official agencies publish predictions of solar growth, often underestimating it. The International Energy Agency (IEA) have consistently increased their estimates for decades, while still falling far short of projecting actual deployment in every forecast. Bloomberg NEF projects an additional 600 GW coming online by 2030 in the United States. By 2050, the IEA foresees solar PV to reach 4.7 terawatts (4,674 GW) in its high-renewable scenario, of which more than half will be deployed in China and India, making solar power the world's largest source of electricity.

Solar PV nameplate capacity

Nameplate capacity denotes the peak power output of power stations in unit watt prefixed as convenient, to e.g. kilowatt (kW), megawatt (MW) and gigawatt (GW). Because power output for renewable sources is variable, a source's average generation is generally significantly lower than the nameplate capacity. In order to have an estimate of the average power output, the capacity can be multiplied by a suitable capacity factor, which takes into account varying conditions - weather, nighttime, latitude, maintenance. Worldwide, the average solar PV capacity factor is 11%. In addition, depending on context, the stated peak power may be prior to a subsequent conversion to alternating current, e.g. for a single photovoltaic panel, or include this conversion and its loss for a grid connected photovoltaic power station.

Wind power has different characteristics, e.g. a higher capacity factor and about four times the 2015 electricity production of solar power. Compared with wind power, photovoltaic power production correlates well with power consumption for air-conditioning in warm countries. As of 2017, a handful of utilities have started combining PV installations with battery banks, thus obtaining several hours of dispatchable generation to help mitigate problems associated with the duck curve after sunset.

Current status

Solar generation by country, 2021

In 2022, the total global photovoltaic capacity increased by 228 GW, with a 24% growth year-on-year of new installations. As a result, the total global capacity exceeded 1,185 GW by the end of the year.

Asia was the biggest installer of solar in 2022, with 60% of new capacity and 60% of total capacity. China alone amounted to over 40% of new solar and almost 40% of total capacity, but only 30% of generation.

North America produced 16% of the world total, led by the United States. North America had the highest capacity factor of all continents in 2022 at 20%, ahead of South America (16%) and the world at large (14%).

Almost all of the solar in Oceania (39TWh) was generated in Australia in 2022, in either case amounting to 3% of the world total. However, Oceania had the highest proportion of electricity that was solar in 2022 at 12%, ahead of Europe (4.9%), Asia (4.9%) and the world overall (4.6%).

History of leading countries

The growth of solar PV on a semi-log scale since 1996

The United States was the leader of installed photovoltaics for many years, and its total capacity was 77 megawatts in 1996, more than any other country in the world at the time. From the late 1990s, Japan was the world's leader of solar electricity production until 2005, when Germany took the lead and by 2016 had a capacity of over 40 gigawatts. In 2015, China surpassed Germany to become the world's largest producer of photovoltaic power, and in 2017 became the first country to surpass 100 GW of installed capacity. Leading countries per capita in 2022 were Australia, Netherlands and Germany.

United States (1954–1996)

The United States, where modern solar PV was invented, led installed capacity for many years. Based on preceding work by Swedish and German engineers, the American engineer Russell Ohl at Bell Labs patented the first modern solar cell in 1946. It was also there at Bell Labs where the first practical c-silicon cell was developed in 1954. Hoffman Electronics, the leading manufacturer of silicon solar cells in the 1950s and 1960s, improved on the cell's efficiency, produced solar radios, and equipped Vanguard I, the first solar powered satellite launched into orbit in 1958.

In 1977 US-President Jimmy Carter installed solar hot water panels on the White House (later removed by President Reagan) promoting solar energy and the National Renewable Energy Laboratory, originally named Solar Energy Research Institute was established at Golden, Colorado. The Carter administration provided major subsidies for research into photovoltaic technology and sought to increase commercialization in the industry.

In the early 1980s, the US accounted for more than 85% of the solar market.

During the Reagan administration, oil prices decreased and the US removed most of its policies that supported its solar industry. Government subsidies were higher in Germany and Japan, which prompted the industrial supply chain to begin moving from the US to those countries.

Japan (1997–2004)

Japan took the lead as the world's largest producer of PV electricity, after the city of Kobe was hit by the Great Hanshin earthquake in 1995. Kobe experienced severe power outages in the aftermath of the earthquake, and PV systems were then considered as a temporary supplier of power during such events, as the disruption of the electric grid paralyzed the entire infrastructure, including gas stations that depended on electricity to pump gasoline. Moreover, in December of that same year, an accident occurred at the multibillion-dollar experimental Monju Nuclear Power Plant. A sodium leak caused a major fire and forced a shutdown (classified as INES 1). There was massive public outrage when it was revealed that the semigovernmental agency in charge of Monju had tried to cover up the extent of the accident and resulting damage. Japan remained world leader in photovoltaics until 2004, when its capacity amounted to 1,132 megawatts. Then, focus on PV deployment shifted to Europe.

Germany (2005–2014)

In 2005, Germany took the lead from Japan. With the introduction of the Renewable Energy Act in 2000, feed-in tariffs were adopted as a policy mechanism. This policy established that renewables have priority on the grid, and that a fixed price must be paid for the produced electricity over a 20-year period, providing a guaranteed return on investment irrespective of actual market prices. As a consequence, a high level of investment security lead to a soaring number of new photovoltaic installations that peaked in 2011, while investment costs in renewable technologies were brought down considerably. In 2016 Germany's installed PV capacity was over the 40 GW mark.

China (2015–present)

China surpassed Germany's capacity by the end of 2015, becoming the world's largest producer of photovoltaic power. China's rapid PV growth continued in 2016 – with 34.2 GW of solar photovoltaics installed. The quickly lowering feed in tariff rates at the end of 2015 motivated many developers to secure tariff rates before mid-year 2016 – as they were anticipating further cuts (correctly so). During the course of the year, China announced its goal of installing 100 GW during the next Chinese Five Year Economic Plan (2016–2020). China expected to spend ¥1 trillion ($145B) on solar construction during that period. Much of China's PV capacity was built in the relatively less populated west of the country whereas the main centres of power consumption were in the east (such as Shanghai and Beijing). Due to lack of adequate power transmission lines to carry the power from the solar power plants, China had to curtail its PV generated power.

China continues to be the global leader in solar power generation and production as of at least 2024. China has one third of the world's installed solar panel capacity and is the largest domestic market for solar panels. 80% of the world's production in the solar industry is made by Chinese companies and their subsidiaries. Chinese firms are the most significant enterprises in almost all parts of the solar manufacturing supply chain, including polysilicon, silicon wafers, batteries, and photovoltaic modules.

History of market development

Prices and costs (1977–present)

Swanson's law–stating that solar module prices have dropped about 20% for each doubling of installed capacity—defines the "learning curve" of solar photovoltaics.
Price decline of c-Si solar cells
Type of cell or module Price per Watt
Multi-Si Cell (≥18.6%) $0.071
Mono-Si Cell (≥20.0%) $0.090
G1 Mono-Si Cell (>21.7%) $0.099
M6 Mono-Si Cell (>21.7%) $0.100
275W - 280W (60P) Module $0.176
325W - 330W (72P) Module $0.188
305W - 310W Module $0.240
315W - 320W Module $0.190
>325W - >385W Module $0.200
Source: EnergyTrend, price quotes, average prices, 13 July 2020[42] 

The average price per watt dropped drastically for solar cells in the decades leading up to 2017. While in 1977 prices for crystalline silicon cells were about $77 per watt, average spot prices in August 2018 were as low as $0.13 per watt or nearly 600 times less than forty years ago. Prices for thin-film solar cells and for c-Si solar panels were around $.60 per watt. Module and cell prices declined even further after 2014 (see price quotes in table).

This price trend was seen as evidence supporting Swanson's law (an observation similar to the famous Moore's Law) that states that the per-watt cost of solar cells and panels fall by 20 percent for every doubling of cumulative photovoltaic production. A 2015 study showed price/kWh dropping by 10% per year since 1980, and predicted that solar could contribute 20% of total electricity consumption by 2030.

The followed figures for select countries represent the cost per kilowatt of utility-scale solar generation, as well as price per kilowatt-hour in 2022 and a comparison with 2010. Dollars are in 2022 international dollars. Data are from IRENA.

Country $ / kW
2022
$ / kWh
2022
$/kWh
2010
%
down
Australia 923 0.041 0.453 -91%
China 715 0.037 0.331 -89%
France 1,157 0.062 0.423 -85%
Germany 996 0.080 0.401 -80%
India 640 0.037 0.376 -90%
South Korea 1,338 0.074 0.482 -85%
Spain 778 0.046 0.348 -87%
United States 1,119 0.058 0.235 -75%

Technologies (1980s–present)

Global photovoltaics market share by technology 1980-2021. 

During the 1980s, Professor Martin Green developed numerous technologies which made solar power generation more efficient. Many of Green's students later became important in China's solar industry, including Shi Zhengrong (who founded Suntech with the support of Wuxi city government).

There were significant advances in conventional crystalline silicon (c-Si) technology in the years leading up to 2017. The falling cost of the polysilicon since 2009, that followed after a period of severe shortage (see below) of silicon feedstock, pressure increased on manufacturers of commercial thin-film PV technologies, including amorphous thin-film silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS), led to the bankruptcy of several thin-film companies that had once been highly touted. The sector faced price competition from Chinese crystalline silicon cell and module manufacturers, and some companies together with their patents were sold below cost.

Global PV market by technology in 2021.
  1. CdTe (4.1%)
  2. a-Si (0.1%)
  3. CIGS (0.8%)
  4. mono-Si (82%)
  5. multi-Si (13%)

In 2013 thin-film technologies accounted for about 9 percent of worldwide deployment, while 91 percent was held by crystalline silicon (mono-Si and multi-Si). With 5 percent of the overall market, CdTe held more than half of the thin-film market, leaving 2 percent to each CIGS and amorphous silicon.

Copper indium gallium selenide (CIGS) is the name of the semiconductor material on which the technology is based. One of the largest producers of CIGS photovoltaics in 2015 was the Japanese company Solar Frontier with a manufacturing capacity in the gigawatt-scale. Their CIS line technology included modules with conversion efficiencies of over 15%. The company profited from the booming Japanese market and attempted to expand its international business. However, several prominent manufacturers could not keep up with the advances in conventional crystalline silicon technology. The company Solyndra ceased all business activity and filed for Chapter 11 bankruptcy in 2011, and Nanosolar, also a CIGS manufacturer, closed its doors in 2013. Although both companies produced CIGS solar cells, it has been pointed out, that the failure was not due to the technology but rather because of the companies themselves, using a flawed architecture, such as, for example, Solyndra's cylindrical substrates.
The U.S.-company First Solar, a leading manufacturer of CdTe, built several of the world's largest solar power stations, such as the Desert Sunlight Solar Farm and Topaz Solar Farm, both in the Californian desert with 550 MW capacity each, as well as the 102 MWAC Nyngan Solar Plant in Australia (the largest PV power station in the Southern Hemisphere at the time) commissioned in mid-2015. The company was reported in 2013 to be successfully producing CdTe-panels with a steadily increasing efficiency and declining cost per watt. CdTe was the lowest energy payback time of all mass-produced PV technologies, and could be as short as eight months in favorable locations. The company Abound Solar, also a manufacturer of cadmium telluride modules, went bankrupt in 2012.
In 2012, ECD solar, once one of the world's leading manufacturer of amorphous silicon (a-Si) technology, filed for bankruptcy in Michigan, United States. Swiss OC Oerlikon divested its solar division that produced a-Si/μc-Si tandem cells to Tokyo Electron Limited. Other companies that left the amorphous silicon thin-film market include DuPont, BP, Flexcell, Inventux, Pramac, Schuco, Sencera, EPV Solar, NovaSolar (formerly OptiSolar) and Suntech Power that stopped manufacturing a-Si modules in 2010 to focus on crystalline silicon solar panels. In 2013, Suntech filed for bankruptcy in China.

Silicon shortage (2005–2008)

Polysilicon prices since 2004. As of July 2020, the ASP for polysilicon stands at $6.956/kg

In the early 2000s, prices for polysilicon, the raw material for conventional solar cells, were as low as $30 per kilogram and silicon manufacturers had no incentive to expand production.

However, there was a severe silicon shortage in 2005, when governmental programmes caused a 75% increase in the deployment of solar PV in Europe. In addition, the demand for silicon from semiconductor manufacturers was growing. Since the amount of silicon needed for semiconductors makes up a much smaller portion of production costs, semiconductor manufacturers were able to outbid solar companies for the available silicon in the market.

Initially, the incumbent polysilicon producers were slow to respond to rising demand for solar applications, because of their painful experience with over-investment in the past. Silicon prices sharply rose to about $80 per kilogram, and reached as much as $400/kg for long-term contracts and spot prices. In 2007, the constraints on silicon became so severe that the solar industry was forced to idle about a quarter of its cell and module manufacturing capacity—an estimated 777 MW of the then available production capacity. The shortage also provided silicon specialists with both the cash and an incentive to develop new technologies and several new producers entered the market. Early responses from the solar industry focused on improvements in the recycling of silicon. When this potential was exhausted, companies have been taking a harder look at alternatives to the conventional Siemens process.

As it takes about three years to build a new polysilicon plant, the shortage continued until 2008. Prices for conventional solar cells remained constant or even rose slightly during the period of silicon shortage from 2005 to 2008. This is notably seen as a "shoulder" that sticks out in the Swanson's PV-learning curve and it was feared that a prolonged shortage could delay solar power becoming competitive with conventional energy prices without subsidies.

In the meantime the solar industry lowered the number of grams-per-watt by reducing wafer thickness and kerf loss, increasing yields in each manufacturing step, reducing module loss, and raising panel efficiency. Finally, the ramp up of polysilicon production alleviated worldwide markets from the scarcity of silicon in 2009 and subsequently lead to an overcapacity with sharply declining prices in the photovoltaic industry for the following years.

Solar overcapacity (2009–2013)

As the polysilicon industry had started to build additional large production capacities during the shortage period, prices dropped as low as $15 per kilogram forcing some producers to suspend production or exit the sector. Prices for silicon stabilized around $20 per kilogram and the booming solar PV market helped to reduce the enormous global overcapacity from 2009 onwards. However, overcapacity in the PV industry continued to persist. In 2013, global record deployment of 38 GW (updated EPIA figure) was still much lower than China's annual production capacity of approximately 60 GW. Continued overcapacity was further reduced by significantly lowering solar module prices and, as a consequence, many manufacturers could no longer cover costs or remain competitive. As worldwide growth of PV deployment continued, the gap between overcapacity and global demand was expected in 2014 to close in the next few years.

IEA-PVPS published in 2014 historical data for the worldwide utilization of solar PV module production capacity that showed a slow return to normalization in manufacture in the years leading up to 2014. The utilization rate is the ratio of production capacities versus actual production output for a given year. A low of 49% was reached in 2007 and reflected the peak of the silicon shortage that idled a significant share of the module production capacity. As of 2013, the utilization rate had recovered somewhat and increased to 63%.

Anti-dumping duties (2012–present)

After anti-dumping petition were filed and investigations carried out, the United States imposed tariffs of 31 percent to 250 percent on solar products imported from China in 2012. A year later, the EU also imposed definitive anti-dumping and anti-subsidy measures on imports of solar panels from China at an average of 47.7 percent for a two-year time span.

Shortly thereafter, China, in turn, levied duties on U.S. polysilicon imports, the feedstock for the production of solar cells. In January 2014, the Chinese Ministry of Commerce set its anti-dumping tariff on U.S. polysilicon producers, such as Hemlock Semiconductor Corporation to 57%, while other major polysilicon producing companies, such as German Wacker Chemie and Korean OCI were much less affected. All this has caused much controversy between proponents and opponents and was subject of debate.

History of deployment

2016-2020 development of the Bhadla Solar Park (India), documented on Sentinel-2 satellite imagery

Deployment figures on a global, regional and nationwide scale are well documented since the early 1990s. While worldwide photovoltaic capacity grew continuously, deployment figures by country were much more dynamic, as they depended strongly on national policies. A number of organizations release comprehensive reports on PV deployment on a yearly basis. They include annual and cumulative deployed PV capacity, typically given in watt-peak, a break-down by markets, as well as in-depth analysis and forecasts about future trends.

Ediacaran biota

From Wikipedia, the free encyclopedia
Life in the Ediacaran Period as imagined by researchers in 1980.

The Ediacaran (/ˌdiˈækərən/; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–538.8 Mya). These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

The Ediacaran biota may have undergone evolutionary radiation in a proposed event called the Avalon explosion, 575 million years ago. This was after the Earth had thawed from the Cryogenian period's extensive glaciation. This biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion. Most of the currently existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have almost completely replaced the organisms that dominated the Ediacaran fossil record, although relationships are still a matter of debate.

The organisms of the Ediacaran Period first appeared around 600 million years ago and flourished until the cusp of the Cambrian 538.8 million years ago, when the characteristic communities of fossils vanished. A diverse Ediacaran community was discovered in 1995 in Sonora, Mexico, and is approximately 555 million years in age, roughly coeval with Ediacaran fossils of the Ediacara Hills in South Australia and the White Sea on the coast of Russia. While rare fossils that may represent survivors have been found as late as the Middle Cambrian (510–500 Mya), the earlier fossil communities disappear from the record at the end of the Ediacaran leaving only curious fragments of once-thriving ecosystems. Multiple hypotheses exist to explain the disappearance of this biota, including preservation bias, a changing environment, the advent of predators and competition from other life-forms. A sampling, reported in 2018, of late Ediacaran strata across the scattered remnants of Baltica (< 560 Mya) suggests the flourishing of the organisms coincided with conditions of low overall productivity with a very high percentage produced by bacteria, which may have led to high concentrations of dissolved organic material in the oceans.

Determining where Ediacaran organisms fit in the tree of life has proven challenging; it is not even established that most of them were animals, with suggestions that they were lichens (fungus-alga symbionts), algae, protists known as foraminifera, fungi or microbial colonies, or hypothetical intermediates between plants and animals. The morphology and habit of some taxa (e.g. Funisia dorothea) suggest relationships to Porifera or Cnidaria (e.g. Auroralumina). Kimberella may show a similarity to molluscs, and other organisms have been thought to possess bilateral symmetry, although this is controversial. Most macroscopic fossils are morphologically distinct from later life-forms: they resemble discs, tubes, mud-filled bags or quilted mattresses. Due to the difficulty of deducing evolutionary relationships among these organisms, some palaeontologists have suggested that these represent completely extinct lineages that do not resemble any living organism. Palaeontologist Adolf Seilacher proposed a separate subkingdom level category Vendozoa (now renamed Vendobionta) in the Linnaean hierarchy for the Ediacaran biota. If these enigmatic organisms left no descendants, their strange forms might be seen as a "failed experiment" in multicellular life, with later multicellular life evolving independently from unrelated single-celled organisms. A 2018 study confirmed that one of the period's most-prominent and iconic fossils, Dickinsonia, included cholesterol, suggesting affinities to animals, fungi, or red algae.

History

The first Ediacaran fossils discovered were the disc-shaped Aspidella terranovica in 1868. Their discoverer, Scottish geologist Alexander Murray, found them useful aids for correlating the age of rocks around Newfoundland. However, since they lay below the "Primordial Strata" of the Cambrian that was then thought to contain the very first signs of animal life, a proposal four years after their discovery by Elkanah Billings that these simple forms represented fauna was dismissed by his peers. Instead, they were interpreted as gas escape structures or inorganic concretions. No similar structures elsewhere in the world were then known and the one-sided debate soon fell into obscurity. In 1933, Georg Gürich discovered specimens in Namibia but assigned them to the Cambrian Period. In 1946, Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia's Flinders Ranges, which were at the time believed to be Early Cambrian.

Palaeontologist Guy Narbonne examining Ediacaran fossils in Newfoundland

It was not until the British discovery of the iconic Charnia that the Precambrian was seriously considered as containing life. This frond-shaped fossil was found in England's Charnwood Forest first by a 15 year-old girl in 1956 (Tina Negus, who was not believed) and then the next year by a group of three schoolboys including 15 year-old Roger Mason. Due to the detailed geological mapping of the British Geological Survey, there was no doubt these fossils sat in Precambrian rocks. Palaeontologist Martin Glaessner finally, in 1959, made the connection between this and the earlier finds and with a combination of improved dating of existing specimens and an injection of vigour into the search, many more instances were recognised.

All specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, making interpretation difficult. S.B. Misra's discovery of fossiliferous ash-beds at the Mistaken Point assemblage in Newfoundland changed all this as the delicate detail preserved by the fine ash allowed the description of features that were previously undiscernible. It was also the first discovery of Ediacarans in deep water sediments.

Poor communication, combined with the difficulty in correlating globally distinct formations, led to a plethora of different names for the biota. In 1960 the French name "Ediacarien" – after the Ediacara Hills – was added to the competing terms "Sinian" and "Vendian" for terminal-Precambrian rocks, and these names were also applied to the life-forms. "Ediacaran" and "Ediacarian" were subsequently applied to the epoch or period of geological time and its corresponding rocks. In March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming the terminal period of the Neoproterozoic after the Australian locality.

The term "Ediacaran biota" and similar ("Ediacara" / "Ediacaran" / "Ediacarian" / "Vendian" and "fauna" / "biota") has, at various times, been used in a geographic, stratigraphic, taphonomic, or biological sense, with the latter the most common in modern literature.

Preservation

Microbial mats

Modern cyanobacterial-algal mat, salty lake on the White Sea seaside

Microbial mats are areas of sediment stabilised by the presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a thin layer of sediment but this is an illusion caused by the colony's growth; individuals do not, themselves, move. If too thick a layer of sediment is deposited before they can grow or reproduce through it, parts of the colony will die leaving behind fossils with a characteristically wrinkled ("elephant skin") and tubercular texture.

Some Ediacaran strata with the texture characteristics of microbial mats contain fossils, and Ediacaran fossils are almost always found in beds that contain these microbial mats. Although microbial mats were once widespread before the Cambrian substrate revolution, the evolution of grazing organisms vastly reduced their numbers. These communities are now limited to inhospitable refugia, such as the stromatolites found in Hamelin Pool Marine Nature Reserve in Shark Bay, Western Australia, where the salt levels can be twice those of the surrounding sea.

Fossilization

The fossil Charniodiscus is barely distinguishable from the "elephant skin" texture on this cast.

The preservation of Ediacaran fossils is of interest, since as soft-bodied organisms they would normally not fossilize. Further, unlike later soft-bodied fossil biota such as the Burgess Shale or Solnhofen Limestone, the Ediacaran biota is not found in a restricted environment subject to unusual local conditions: they are global. The processes that were operating must therefore have been systemic and worldwide. Something about the Ediacaran Period permitted these delicate creatures to be left behind; the fossils may have been preserved by virtue of rapid covering by ash or sand, trapping them against the mud or microbial mats on which they lived. Their preservation was possibly enhanced by the high concentration of silica in the oceans before silica-secreting organisms such as sponges and diatoms became prevalent. Ash beds provide more detail and can readily be dated to the nearest million years or better using radiometric dating. However, it is more common to find Ediacaran fossils under sandy beds deposited by storms or in turbidites formed by high-energy bottom-scraping ocean currents. Soft-bodied organisms today rarely fossilize during such events, but the presence of widespread microbial mats probably aided preservation by stabilising their impressions in the sediment below.

Scale of preservation

The rate of cementation of the overlying substrate relative to the rate of decomposition of the organism determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the overlying sediment was cemented, whereupon ash or sand slumped in to fill the void, leaving a cast of the organism's underside. Conversely, quilted fossils tended to decompose after the cementation of the overlying sediment; hence their upper surfaces are preserved. Their more resistant nature is reflected in the fact that, in rare occasions, quilted fossils are found within storm beds as the high-energy sedimentation did not destroy them as it would have the less-resistant discs. Further, in some cases, the bacterial precipitation of minerals formed a "death mask", ultimately leaving a positive, cast-like impression of the organism.

Morphology

Forms of Ediacaran fossil
The earliest discovered potential embryo, preserved within an acanthomorphic acritarch. The term 'acritarch' describes a range of unclassified cell-like fossils. The earliest discovered potential embryo, preserved within an acanthomorphic acritarch.
Tateana inflata ('Cyclomedusa' radiata) were originally believed to have been Medusoids, although recent research suggests that they were holdfasts of Petalonamids. Tateana inflata (= 'Cyclomedusa' radiata) is attachment disk of unknown organism
A cast of Charnia, the first accepted complex Precambrian organism. Charnia was once interpreted as a relative of the sea pens. A cast of Charnia
Dickinsonia displays the characteristic quilted appearance of Ediacaran enigmata. A cast of Dickinsonia
Spriggina was originally interpreted as annelid or arthropod. However, lack of known limbs, and glide reflected isomers instead of true segments, rejects any such classification despite some superficial resemblance. Spriggina may be one of the predators that led to the demise of the Ediacaran fauna
Late Ediacaran Archaeonassa-type trace fossils are commonly preserved on the top surfaces of sandstone strata. Late Ediacaran Archaeonassa-type trace fossils are commonly preserved on the top surfaces of sandstone strata
Epibaion waggoneris, chain of trace platforms and the imprint of the body of Yorgia waggoneri (right), which created these traces on microbial mat. Yorgia chain of trace platforms terminate by the body of the animal (right).

The Ediacaran biota exhibited a vast range of morphological characteristics. Size ranged from millimetres to metres; complexity from "blob-like" to intricate; rigidity from sturdy and resistant to jelly-soft. Almost all forms of symmetry were present. These organisms differed from earlier, mainly microbial, fossils in having an organised, differentiated multicellular construction and centimetre-plus sizes.

These disparate morphologies can be broadly grouped into form taxa:

"Embryos"
Recent discoveries of Precambrian multicellular life have been dominated by reports of embryos, particularly from the Doushantuo Formation in China. Some finds generated intense media excitement though some have claimed they are instead inorganic structures formed by the precipitation of minerals on the inside of a hole. Other "embryos" have been interpreted as the remains of the giant sulfur-reducing bacteria akin to Thiomargarita, a view that, while it had enjoyed a notable gain of supporters as of 2007, has since suffered following further research comparing the potential Doushantuo embryos' morphologies with those of Thiomargarita specimens, both living and in various stages of decay. A recent discovery of comparable Ediacaran fossil embryos from the Portfjeld Formation in Greenland has significantly expanded the paleogeograpical occurrence of Doushantuo-type fossil "embryos" with similar biotic forms now reported from differing paleolatitudes.
Microfossils dating from 632.5 million years ago – just 3 million years after the end of the Cryogenian glaciations – may represent embryonic 'resting stages' in the life cycle of the earliest known animals. An alternative proposal is that these structures represent adult stages of the multicellular organisms of this period. Microfossils of Caveasphaera are thought to foreshadow the evolutionary origin of animal-like embryology.
Discs
Circular fossils, such as Ediacaria, Cyclomedusa, and Rugoconites led to the initial identification of Ediacaran fossils as cnidaria, which include jellyfish and corals. Further examination has provided alternative interpretations of all disc-shaped fossils: not one is now confidently recognised as a jellyfish. Alternate explanations include holdfasts and protists; the patterns displayed where two meet have led to many 'individuals' being identified as microbial colonies, and yet others may represent scratch marks formed as stalked organisms spun around their holdfasts.
Bags
Fossils such as Pteridinium preserved within sediment layers resemble "mud-filled bags". The scientific community is a long way from reaching a consensus on their interpretation.
Toroids
The fossil Vendoglossa tuberculata from the Nama Group, Namibia, has been interpreted as a dorso-ventrally compressed stem-group metazoan, with a large gut cavity and a transversely ridged ectoderm. The organism is in the shape of a flattened torus, with the long axis of its toroidal body running through the approximate center of the presumed gut cavity.
Quilted organisms
The organisms considered in Seilacher's revised definition of the Vendobionta share a "quilted" appearance and resembled an inflatable mattress. Sometimes these quilts would be torn or ruptured prior to preservation: Such damaged specimens provide valuable clues in the reconstruction process. For example, the three (or more) petaloid fronds of Swartpuntia germsi could only be recognised in a posthumously damaged specimen – usually multiple fronds were hidden as burial squashed the organisms flat. These organisms appear to form two groups: the fractal rangeomorphs and the simpler erniettomorphs. Including such fossils as the iconic Charnia and Swartpuntia, the group is both the most iconic of the Ediacaran biota and the most difficult to place within the existing tree of life. Lacking any mouth, gut, reproductive organs, or indeed any evidence of internal anatomy, their lifestyle was somewhat peculiar by modern standards; the most widely accepted hypothesis holds that they sucked nutrients out of the surrounding seawater by osmotrophy or osmosis. However, others argue against this.
Non-Vendobionts
Possible early forms of living phyla, excluding them from some definitions of the Ediacaran biota. The earliest such fossil is the reputed bilaterian Vernanimalcula claimed by some, however, to represent the infilling of an egg-sac or acritarch. In 2020, Ikaria wariootia was claimed to represent one of the oldest organisms with anterior and posterior differentiation. Later examples are almost universally accepted as bilaterians and include the mollusc-like Kimberella, Spriggina (pictured) and the shield-shaped Parvancorina whose affinities are currently debated. A suite of fossils known as the small shelly fossils are represented in the Ediacaran, most famously by Cloudina a shelly tube-like fossil that often shows evidence of predatory boring, suggesting that, while predation may not have been common in the Ediacaran Period, it was at least present. Organic microfossils known as small carbonaceous fossils are found in Ediacaran sediments, including the spiral-shaped Cochleatina which spans the Ediacaran–Cambrian boundary. Ediacaria also survived well into the Cambrian. Representatives of modern taxa existed in the Ediacaran, some of which are recognisable today. Sponges, red and green algæ, protists and bacteria are all easily recognisable with some pre-dating the Ediacaran by nearly three billion years. Possible arthropods have also been described. Surface trails left by Treptichnus bear similarities to modern priapulids. Fossils of the hard-shelled foraminifera Platysolenites are known from the latest Ediacaran of western Siberia, coexisting with Cloudina and Namacalathus.
Filaments
Filament-shaped structures in Precambrian fossils have been observed on many occasions. Frondose fossils in Newfoundland have been observed to have developed filamentous bedding planes, inferred to be stolonic outgrowths. A study of Brazilian Ediacaran fossils found filamentous microfossils, suggested to be eukaryotes or large sulfur-oxidizing-bacteria (SOBs). Fungus-like filaments found in the Doushantuo Formation have been interpreted as eukaryotes and possibly fungi, providing possible evidence for the evolution and terrestrialization of fungi ~635 Ma.
Trace fossils
With the exception of some very simple vertical burrows the only Ediacaran burrows are horizontal, lying on or just below the surface of the seafloor. Such burrows have been taken to imply the presence of motile organisms with heads, which would probably have had a bilateral symmetry. This could place them in the bilateral clade of animals but they could also have been made by simpler organisms feeding as they slowly rolled along the sea floor. Putative "burrows" dating as far back as 1,100 million years may have been made by animals that fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean; however their uneven width and tapering ends make a biological origin so difficult to defend that even the original proponent no longer believes they are authentic.
The burrows observed imply simple behaviour, and the complex efficient feeding traces common from the start of the Cambrian are absent. Some Ediacaran fossils, especially discs, have been interpreted tentatively as trace fossils but this hypothesis has not gained widespread acceptance. As well as burrows, some trace fossils have been found directly associated with an Ediacaran fossil. Yorgia and Dickinsonia are often found at the end of long pathways of trace fossils matching their shape; these fossils are thought to be associated with ciliary feeding but the precise method of formation of these disconnected and overlapping fossils largely remains a mystery. The potential mollusc Kimberella is associated with scratch marks, perhaps formed by a radula.

Classification and interpretation

A reconstruction of the Ediacaran biota at the Field Museum in Chicago

Classification of the Ediacarans is inevitably difficult, hence a variety of theories exist as to their placement on the tree of life.

Martin Glaessner proposed in The Dawn of Animal Life (1984) that the Ediacaran biota were recognizable crown group members of modern phyla, but were unfamiliar because they had yet to evolve the characteristic features we use in modern classification.

In 1998 Mark McMenamin claimed Ediacarans did not possess an embryonic stage, and thus could not be animals. He believed that they independently evolved a nervous system and brains, meaning that "the path toward intelligent life was embarked upon more than once on this planet".

In 2018 analysis of ancient sterols was taken as evidence that one of the period's most-prominent and iconic fossils, Dickinsonia, was an early animal.

Cnidarians

A sea pen, a modern cnidarian bearing a passing resemblance to Charnia

Since the most primitive eumetazoans—multi-cellular animals with tissues—are cnidarians, and the first recognized Ediacaran fossil Charnia looks very much like a sea pen, the first attempt to categorise these fossils designated them as jellyfish and sea pens. However, more recent discoveries have established that many of the circular forms formerly considered "cnidarian medusa" are actually holdfasts – sand-filled vesicles occurring at the base of the stem of upright frond-like Ediacarans. A notable example is the form known as Charniodiscus, a circular impression later found to be attached to the long 'stem' of a frond-like organism that now bears the name.

The link between frond-like Ediacarans and sea pens has been thrown into doubt by multiple lines of evidence; chiefly the derived nature of the most frond-like pennatulacean octocorals, their absence from the fossil record before the Tertiary, and the apparent cohesion between segments in Ediacaran frond-like organisms. Some researchers have suggested that an analysis of "growth poles" discredits the pennatulacean nature of Ediacaran fronds.

Protozoans

A single-celled xenophyophore in the Galapagos Rift

Adolf Seilacher has suggested that in the Ediacaran, animals take over from giant protists as the dominant life form. The modern xenophyophores are giant single-celled protozoans found throughout the world's oceans, largely on the abyssal plain. Genomic evidence suggests that the xenophyophores are a specialised group of Foraminifera.

Unique phyla

Seilacher has suggested that the Ediacaran organisms represented a unique and extinct grouping of related forms descended from a common ancestor (clade) and created the kingdom Vendozoa, named after the now-obsolete Vendian era. He later excluded fossils identified as metazoans and relaunched the phylum "Vendobionta", which he described as "quilted" cnidarians lacking stinging cells. This absence precludes the current cnidarian method of feeding, so Seilacher suggested that the organisms may have survived by symbiosis with photosynthetic or chemoautotrophic organisms. Mark McMenamin saw such feeding strategies as characteristic for the entire biota, and referred to the marine biota of this period as a "Garden of Ediacara".

Lichen hypothesis

Greg Retallack's analysis of thin sections and substrates of a variety of Ediacaran fossils. His findings have been disputed by other scientists.

Greg Retallack has proposed that Ediacaran organisms were lichens. He argues that thin sections of Ediacaran fossils show lichen-like compartments and hypha-like wisps of ferruginized clay, and that Ediacaran fossils have been found in strata that he interprets as desert soils.

The suggestion has been disputed by other scientists; some have described the evidence as ambiguous and unconvincing, for instance noting that Dickinsonia fossils have been found on rippled surfaces (suggesting a marine environment), while trace fossils like Radulichnus could not have been caused by needle ice as Retallack has proposed. Ben Waggoner notes that the suggestion would place the root of the Cnidaria back from around 900 mya to between 1500 mya and 2000 mya, contradicting much other evidence. Matthew Nelsen, examining phylogenies of ascomycete fungi and chlorophyte algae (components of lichens), calibrated for time, finds no support for the hypothesis that lichens predated the vascular plants.

Other interpretations

Several classifications have been used to accommodate the Ediacaran biota at some point, from algae, to protozoans, to fungi to bacterial or microbial colonies, to hypothetical intermediates between plants and animals.

A new extant genus discovered in 2014, Dendrogramma, which at the time of discovery appeared to be a basal metazoan but of unknown taxonomic placement, had been noted to have similarities with the Ediacaran fauna. It has since been found to be a siphonophore, possibly even sections of a more complex species.

Origin

It took almost 4 billion years from the formation of the Earth for Ediacaran fossils to first appear, 655 million years ago. While putative fossils are reported from 3,460 million years ago, the first uncontroversial evidence for life is found 2,700 million years ago, and cells with nuclei certainly existed by 1,200 million years ago.

It could be that no special explanation is required: the slow process of evolution simply required 4 billion years to accumulate the necessary adaptations. Indeed, there does seem to be a slow increase in the maximum level of complexity seen over this time, with more and more complex forms of life evolving as time progresses, with traces of earlier semi-complex life such as Nimbia, found in the 610 million year old Twitya formation, and older rocks dating to 770 million years ago in Kazakhstan.

Global ice sheets might have delayed or prevented the establishment of multicellular life.

On the early Earth, reactive elements, such as iron and uranium, existed in a reduced form that would react with any free oxygen produced by photosynthesising organisms. Oxygen would not be able to build up in the atmosphere until all the iron had rusted (producing banded iron formations), and all the other reactive elements had been oxidised. Donald Canfield detected records of the first significant quantities of atmospheric oxygen just before the first Ediacaran fossils appeared – and the presence of atmospheric oxygen was soon heralded as a possible trigger for the Ediacaran radiation. Oxygen seems to have accumulated in two pulses; the rise of small, sessile (stationary) organisms seems to correlate with an early oxygenation event, with larger and mobile organisms appearing around the second pulse of oxygenation. However, the assumptions underlying the reconstruction of atmospheric composition have attracted some criticism, with widespread anoxia having little effect on life where it occurs in the Early Cambrian and the Cretaceous.

Periods of intense cold have also been suggested as a barrier to the evolution of multicellular life. The earliest known embryos, from China's Doushantuo Formation, appear just a million years after the Earth emerged from a global glaciation, suggesting that ice cover and cold oceans may have prevented the emergence of multicellular life.

In early 2008, a team analysed the range of basic body structures ("disparity") of Ediacaran organisms from three different fossil beds: Avalon in Canada, 575 million years ago to 565 million years ago; White Sea in Russia, 560 million years ago to 550 million years ago; and Nama in Namibia, 550 million years ago to 542 million years ago, immediately before the start of the Cambrian. They found that, while the White Sea assemblage had the most species, there was no significant difference in disparity between the three groups, and concluded that before the beginning of the Avalon timespan these organisms must have gone through their own evolutionary "explosion", which may have been similar to the famous Cambrian explosion.

Preservation bias

The paucity of Ediacaran fossils after the Cambrian could simply be due to conditions no longer favoring the fossilization of Ediacaran organisms, which may have continued to thrive unpreserved for a considerable time. However, if they were common, more than the occasional specimen might be expected in exceptionally preserved fossil assemblages (Konservat-Lagerstätten) such as the Burgess Shale and Chengjiang. Although no reports of Ediacara-type organisms in the Cambrian period are widely accepted at present, a few disputed reports have been made, as well as unpublished observations of 'vendobiont' fossils from 535 Ma Orsten-type deposits in China.

Predation and grazing

Kimberella might have had a predatory or grazing lifestyle.

It has been suggested that by the Early Cambrian, organisms higher in the food chain caused the microbial mats to largely disappear. If these grazers first appeared as the Ediacaran biota started to decline, then it may suggest that they destabilised the microbial mats in a "Cambrian substrate revolution", leading to displacement or detachment of the biota; or that the destruction of the microbial substrate destabilized the ecosystem, causing extinctions.

Alternatively, skeletonized animals could have fed directly on the relatively undefended Ediacaran biota. However, if the interpretation of the Ediacaran age Kimberella as a grazer is correct then this suggests that the biota had already had limited exposure to "predation".

Competition

Cambrian animals such as Waptia might have competed with, or fed upon, Ediacaran life-forms.

Increased competition due to the evolution of key innovations among other groups, perhaps as a response to predation, may have driven the Ediacaran biota from their niches. However, the supposed "competitive exclusion" of brachiopods by bivalve molluscs was eventually deemed to be a coincidental result of two unrelated trends.

Change in environmental conditions

Great changes were happening at the end of the Precambrian and the start of the Early Cambrian. The breakup of the supercontinents, rising sea levels (creating shallow, "life-friendly" seas), a nutrient crisis, fluctuations in atmospheric composition, including oxygen and carbon dioxide levels, and changes in ocean chemistry (promoting biomineralisation) could all have played a part.

Assemblages

Late Ediacaran macrofossils are recognized globally in at least 52 formations and a variety of depositional conditions. Each formation is commonly grouped into three main types, known as assemblages and named after typical localities. Each assemblage tends to occupy its own time period and region of morphospace, and after an initial burst of diversification (or extinction) changes little for the rest of its existence.

Avalon assemblage

The Avalon assemblage is defined at Mistaken Point one the Avalon Peninsula of Canada, the oldest locality with a large quantity of Ediacaran fossils. The assemblage is easily dated because it contains many fine ash-beds, which are a good source of zircons used in the uranium-lead method of radiometric dating. These fine-grained ash beds also preserve exquisite detail. Constituents of this biota appear to survive through until the extinction of all Ediacarans at the base of the Cambrian.

One interpretation of the biota is as deep-sea-dwelling rangeomorphs such as Charnia, all of which share a fractal growth pattern. They were probably preserved in situ (without post-mortem transportation), although this point is not universally accepted. The assemblage, while less diverse than the White Sea or Nama assemblages, resembles Carboniferous suspension-feeding communities, which may suggest filter feeding as the assemblage is often found in water too deep for photosynthesis.

White Sea assemblage

The White Sea or Ediacaran assemblage is named after Russia's White Sea or Australia's Ediacara Hills and is marked by much higher diversity than the Avalon or Nama assemblages. In Australia, they are typically found in red gypsiferous and calcareous paleosols formed on loess and flood deposits in an arid cool temperate paleoclimate. Most fossils are preserved as imprints in microbial beds, but a few are preserved within sandy units.

Nama assemblage

The Nama assemblage is best represented in Namibia. It is marked by extreme biotic turnover, with rates of extinction exceeding rates of origination for the whole period. Three-dimensional preservation is most common, with organisms preserved in sandy beds containing internal bedding. Dima Grazhdankin believes that these fossils represent burrowing organisms, while Guy Narbonne maintains they were surface dwellers. These beds are sandwiched between units comprising interbedded sandstones, siltstones and shales—with microbial mats, where present, usually containing the fossils. The environment is interpreted as sand bars formed at the mouth of a delta's distributaries. Mattress-like vendobionts (Ernietta, Pteridinium, Rangea) in these sandstones form a very different assemblage from vermiform fossils (Cloudina, Namacalathus) of Ediacaran "wormworld" in marine dolomite of Namibia.

Significance of assemblages

Since they are globally distributed – described on all continents except Antarctica – geographical boundaries do not appear to be a factor; the same fossils are found at all palaeolatitudes (the latitude where the fossil was created, accounting for continental drift - an application of paleomagnetism) and in separate sedimentary basins. An analysis of one of the White Sea fossil beds, where the layers cycle from continental seabed to inter-tidal to estuarine and back again a few times, found that a specific set of Ediacaran organisms was associated with each environment. However, while there is some delineation in organisms adapted to different environments, the three assemblages are more distinct temporally than paleoenvironmentally. Because of this, the three assemblages are often separated by temporal boundaries rather than environmental ones (timeline at right).

As the Ediacaran biota represent an early stage in multicellular life's history, it is unsurprising that not all possible modes of life are occupied. It has been estimated that of 92 potentially possible modes of life – combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage.

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