Did Earliest Animals Live In Lakes?
Wednesday, 29. July 2009, 18:18:19
For some 3 billion years, single-celled life forms such as bacteria dominated the planet. Then, roughly 600 million years ago, the first multi-cellular animals appeared on the scene, diversifying rapidly. So far it was commonly assumed that animal evolution began in the ocean, with animal life adapting much later in Earth history to terrestrial environments.
Now a team of researchers studying ancient rock samples in South China has found that the first animal fossils in the paleontological record are preserved in ancient lake deposits, in the Doushantuo Formation. It may sound surprising that the first evidence of animals found is associated with lakes, a far more variable environment than the ocean. The scientists detailed their findings online July 27 in the Proceedings of the National Academy of Sciences(PNAS). The study raises questions such as what aspects of the Earth’s environment changed to enable animal evolution.
In their research, the authors focused on South China’s Doushantuo Formation, one of the oldest fossil beds that houses highly preserved fossils dated to about 600 million years ago. Taken as a whole, the Doushantuo Formation ranges from about 590 Ma at its base to about 565 Ma at its top. The studied beds have no adult fossils. Instead, many of the fossils appear as bundles of cells interpreted to be animal embryos.
Smectite is abundant in the region. Smectite is a clay mineral that normally is transformed into other types of clay in rocks of this age. The smectite in these South China rocks, however, underwent no such transformation and have a special chemistry that, for the smectite to form, requires specific conditions in the water – conditions commonly found in salty, alkaline lakes.
The rocks’ minerals and geochemistry are not compatible with deposition in seawater. Smectite is only found in some locations in South China, and not uniformly as one would expect for marine deposits. This was an important indicator that the rocks hosting the fossils were not marine in origin. Taken together, several lines of evidence indicated that these early animals lived in a lake environment.
The study raises questions such as what aspects of the Earth’s environment changed to enable animal evolution. If animals did first develop in lakes, one aspect of lake environments that could have spurred on their evolution is how much easier it is for air to percolate through them, given how much shallower they typically are than the ocean.
Reference:
Bristow et al.
Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation
Published online before print
PNAS July 29, 2009
doi: 10.1073/pnas.0901080106
• http://newsroom.ucr.edu/news_item.html?action=page&id=2144
• http://www.sciencedaily.com/releases/2009/07/090727191732.htm
• http://www.livescience.com/animals/090727-first-life.html
• http://news.softpedia.com/news/Early-Animals-Lived-in-Lakes-not-Oceans-117691.shtml
• http://www.terradaily.com/reports/Earliest_Animals_Lived_In_A_Lake_Environment_999.html
• http://news.yahoo.com/s/livescience/oldestanimalfossilsfoundinlakesnotoceans
Now a team of researchers studying ancient rock samples in South China has found that the first animal fossils in the paleontological record are preserved in ancient lake deposits, in the Doushantuo Formation. It may sound surprising that the first evidence of animals found is associated with lakes, a far more variable environment than the ocean. The scientists detailed their findings online July 27 in the Proceedings of the National Academy of Sciences(PNAS). The study raises questions such as what aspects of the Earth’s environment changed to enable animal evolution.
In their research, the authors focused on South China’s Doushantuo Formation, one of the oldest fossil beds that houses highly preserved fossils dated to about 600 million years ago. Taken as a whole, the Doushantuo Formation ranges from about 590 Ma at its base to about 565 Ma at its top. The studied beds have no adult fossils. Instead, many of the fossils appear as bundles of cells interpreted to be animal embryos.
Smectite is abundant in the region. Smectite is a clay mineral that normally is transformed into other types of clay in rocks of this age. The smectite in these South China rocks, however, underwent no such transformation and have a special chemistry that, for the smectite to form, requires specific conditions in the water – conditions commonly found in salty, alkaline lakes.
The rocks’ minerals and geochemistry are not compatible with deposition in seawater. Smectite is only found in some locations in South China, and not uniformly as one would expect for marine deposits. This was an important indicator that the rocks hosting the fossils were not marine in origin. Taken together, several lines of evidence indicated that these early animals lived in a lake environment.
The study raises questions such as what aspects of the Earth’s environment changed to enable animal evolution. If animals did first develop in lakes, one aspect of lake environments that could have spurred on their evolution is how much easier it is for air to percolate through them, given how much shallower they typically are than the ocean.
Reference:
Bristow et al.
Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation
Published online before print
PNAS July 29, 2009
doi: 10.1073/pnas.0901080106
• http://newsroom.ucr.edu/news_item.html?action=page&id=2144
• http://www.sciencedaily.com/releases/2009/07/090727191732.htm
• http://www.livescience.com/animals/090727-first-life.html
• http://news.softpedia.com/news/Early-Animals-Lived-in-Lakes-not-Oceans-117691.shtml
• http://www.terradaily.com/reports/Earliest_Animals_Lived_In_A_Lake_Environment_999.html
• http://news.yahoo.com/s/livescience/oldestanimalfossilsfoundinlakesnotoceans
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