Earliest Animal Life

[ramonmercado]

Clay Major Contributor To Oxygen That Enabled Early Animal Life

Martin Kennedy, associate professor in the Department of Earth Sciences at UCR, led a study that identifies clay as a major contributor to oxygen that enabled early animal life on Earth.
by Staff Writers
Riverside CA (SPX) Feb 03, 2006
A UC Riverside-led study has found that clay made animal life possible on Earth. A sudden increase in oxygen in the Earth's recent geological history, widely considered necessary for the expansion of animal life, occurred just as the rate of clay formation on the Earth's surface also increased, the researchers report.
"Our study shows for the first time that the initial soils covering the terrestrial surface of Earth increased the production of clay minerals and provided the critical geochemical processes necessary to oxygenate the atmosphere and support multicellular animal life," said Martin Kennedy, an associate professor of sedimentary geology and geochemistry at UCR, who led the study.

Study results appear in the Feb. 2 issue of Science Express, which provides electronic publication of selected Science papers in advance of print.

Analyzing old sedimentary rocks, the researchers found evidence of an increase in clay mineral deposition in the oceans during a 200 million year period that fell between 1.1 to 0.54 billion years ago – a stretch of time known as the late Precambrian when oxygen suddenly increased in the Earth's atmosphere. The increases in clay formation and oxygen shortly preceded – in geological time – the first animal fossils about 600 million years ago.

"This study shows how we can use principles developed from the study of modern environments to understand the very complex origin of life on our planet – studying a time in history that has left us only a scanty record of its conditions," said Lawrence M. Mayer, a professor of oceanography at the University of Maine and a co-author of the Science paper.

Clay minerals form in soils through biological interactions with weathering rocks and are then eroded and flushed to the sea, where they are deposited as mud. Because clay minerals are chemically reactive, they attract and absorb organic matter in ocean water, and physically shelter and preserve it.

The UCR-led study emphasizes the possibility that colonization of the land surface by a primitive terrestrial ecosystem (possibly involving fungi) accelerated clay formation, as happens in modern soils.

Upon being washed down to the sea, the clay minerals were responsible for preserving more organic matter in marine sediments than had been the case in the absence of clays. Organic matter preservation results in an equal portion of oxygen released to the atmosphere through the chemical reaction of photosynthesis. Thus an increase in the burial of organic carbon made it possible for more oxygen to escape into the atmosphere, the researchers posit.

"One of the things we least understand is why animals evolved so late in Earth history," Kennedy said. "Why did animals wait until the eleventh hour, whereas evidence for more primitive life dates back to billions of years? One of the best bets to explain the difference is an increase in oxygen concentration in the atmosphere, which is necessary for animal life and was likely too low through most of Earth's history."

To establish a change in clay abundance during the late Precambrian, the researchers studied thick sections of ancient sedimentary rocks in Australia, China and Scandinavia, representing a history of hundreds of millions of years, to identify when clay minerals increased in the sediment from almost nothing to modern depositional levels.

"We predicted we would only find a significant percentage of clay minerals in sediments toward the end of the Precambrian, when complex life arose, while earlier sediments would have less clay content," Kennedy said. "This test is easier than it sounds. Because clay minerals make up the bulk of sediment deposited today, we are saying that it should be largely absent in ancient rocks. And this is just what one finds."

The study attracted the attention of the National Aeronautics and Space Administration during the proposal stage, and the agency helped fund the research.

"NASA is interested in what conditions to look for on other planets that might lead to the arrival of life," Kennedy said. "What are the processes? Using Earth as our most detailed study site, what are the necessary steps a planet needs to go through to enable complex animal life to arise? If oxygen is the metabolic pathway, then we need to know what conditions have to allow for that to happen. The geologic record provides us with a record of these steps that occurred on Earth."

UCR's Mary Droser and David Mrofka; and David Pevear collaborated on the study, which was supported also by the National Science Foundation.


Clay

 

[Anonymous]

Bioliths.

 

[EnolaGaia]

In 2009 researchers announced the detection of geochemical traces they attributed to demosponges. On this basis they claimed the discovery as evidence of animal life circa 635 million years ago - a radical shift from prior beliefs.

https://www.nature.com/articles/nature07673

This raised a lot of issues, because there wasn't any fossil (etc.) evidence for animal life that could have led to demosponges that long ago.

As it turns out ...

Newly published research demonstrates that the chemical traces interpreted as demosponge products could have been - and probably were - generated by algae. These new findings suggest animal life hadn't developed as far back as the 2009 research had suggested.

The World's Oldest Evidence of Animals Might Be From a Very Different Organism

The origins of life, a few billion years ago, were humble. Single-celled organisms squirming in the ooze, over millions and billions of years developing into multi-celled plants and, eventually, animals.

But when and how these evolutionary spurts occurred has been difficult to puzzle out. Organic material doesn't necessarily preserve well, and when it does, we don't always identify it correctly.

New research, however, brings us a little closer to the truth. Fossils from 635 million years ago that had previously been identified as animal in origin could actually have been made by a very different organism - algae.

"It brings the oldest evidence for animals nearly 100 million years closer to the present day," said paleobiogeochemist Lennart van Maldegem of the Australian National University in Australia.

"We were able to demonstrate that certain molecules from common algae can be altered by geological processes - leading to molecules which are indistinguishable from those produced by sponge-like animals."

According to molecular clock studies - a technique that uses the mutation rates of biomolecules to back-date genetic divergence - animal life emerged relatively late in the evolutionary timeline. Our earliest evidence of life is from around 3.4 to 3.5 billion years ago, ancient records of single-celled organisms.

Plants emerged a fair bit later, around 1.6 billion years ago. And it took as much as another billion years for animals to emerge; between around 900 and 635 million years ago, according to those molecular clock studies. But the fossil record seemed absolutely bereft of evidence of animals in that timeframe.

Until 2009, when scientists revealed that they had found abundant quantities of 24-isopropylcholestanes in Neoproterozoic rock, dating back to more than 635 million years ago.

These are thought to originate almost exclusively in demosponges, which produce a type of lipid with 30 carbon atoms and unusual side chains, called C30 sterols. The fossil products of these sterols are C30 steranes, like the 24-isopropylcholestane interpreted as evidence of Neoproterozoic animal life.

In two new papers in Nature Ecology & Evolution, however, teams of researchers show that we cannot conclusively interpret C30 steranes as faunal in origin, and this would neatly resolve another mystery surrounding that interpretation. ...

FULL STORY:
https://www.sciencealert.com/the-world-s-oldest-evidence-of-animals-might-actually-be-algae

 

[EnolaGaia]

Here are the bibliographic details and abstracts of the newly published papers regarding misinterpretation of geochemical traces as evidence of demosponges.

Bobrovskiy, I., Hope, J.M., Nettersheim, B.J. et al.
Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record.
Nat Ecol Evol (2020).
https://doi.org/10.1038/s41559-020-01334-7

Abstract
The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C30 fossil sterol molecules have been suggested to reflect an important ecological role of demosponges as the first abundant animals by the end of the Cryogenian period (>635 million years ago). Here, we demonstrate that C30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C29 sterols of chlorophyte algae, the dominant eukaryotes at that time. These findings reconcile biomarker evidence with the geological record and revert the oldest evidence for animals back into the latest Ediacaran.

SOURCE: https://www.nature.com/articles/s41559-020-01334-7

--------------

van Maldegem, L.M., Nettersheim, B.J., Leider, A. et al.
Geological alteration of Precambrian steroids mimics early animal signatures.
Nat Ecol Evol (2020).
https://doi.org/10.1038/s41559-020-01336-5

Abstract
The absence of unambiguous animal body fossils in rocks older than the late Ediacaran has rendered fossil lipids the most promising tracers of early organismic complexity. Yet much debate surrounds the various potential biological sources of putative metazoan steroids found in Precambrian rocks. Here we show that 26-methylated steranes—hydrocarbon structures currently attributed to the earliest animals—can form via geological alteration of common algal sterols, which carries important implications for palaeo-ecological interpretations and inhibits the use of such unconventional ‘sponge’ steranes for reconstructing early animal evolution.

SOURCE: https://www.nature.com/articles/s41559-020-01336-5

 

[uair01]

The origin of multicellular life, one of the most important developments in Earth’s history, could have occurred with surprising speed, US researchers have shown. In the lab, a single-celled yeast (Saccharomyces cerevisiae) took less than 60 days to evolve into many-celled clusters that behaved as individuals. The clusters even developed a primitive division of labour, with some cells dying so that others could grow and reproduce.

https://www.nature.com/articles/nature.2012.9810

Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth.

https://www.pnas.org/doi/full/10.1073/pnas.1115323109

https://ratclifflab.biosci.gatech.edu/current-projects/