A new study highlights how extreme conditions during Snowball Earth may have driven the evolution of multicellular organisms, offering new insights into Earth’s evolutionary history and tools for future research.
For a billion years, single-celled eukaryotes ruled the planet. Then around 700 million years ago during Snowball Earth — a geologic era when glaciers may have stretched as far as the Equator — a new creature burst into existence: the multicellular organism.
Why did multicellularity arise? Solving that mystery may help pinpoint life on other planets and explain the vast diversity and complexity seen on Earth today, from sea sponges to redwoods to human society.
Common wisdom holds that oxygen levels had to hit a certain threshold for single cells to form multicellular colonies. But the oxygen story doesn’t fully explain why multicellular ancestors of animals, plants, and fungi appeared simultaneously, and why the transition to multicellularity took more than 1 billion years.
Snowball Earth’s Influence on Evolution
A new paper in Proceedings of the Royal Society B shows how specific physical conditions of Snowball Earth — especially ocean viscosity and resource deprivation — could have driven eukaryotes to turn multicellular.
“It seems almost counterintuitive that these really harsh conditions, this frozen planet, could actually select for larger, more complex organisms, rather than causing species to go extinct or reduce in size,” says former SFI Undergraduate Complexity Researcher William Crockett, corresponding author on the paper and Ph.D. student at MIT.
Using scaling theories, the authors found that a hypothetical early animal ancestor (reminiscent of swimming algae that eat prey instead of photosynthesizing) would swell in size and complexity under Snowball Earth pressures. By contrast, a single-celled organism that moves and feeds via diffusion, like a bacterium, would grow smaller.
“The world is different after Snowball Earth because there’s a new form of life on the planet. One of the central questions of evolution is how do you go from nothing on a planet to things like us, and to societies? Is all of that an accident? We think it’s not luck: there are ways to predict these major transitions,” says senior author and SFI Professor Christopher Kempes.
The Impact of Iced-Over Oceans
The study shows how the iced-over oceans during Snowball Earth would have blocked sunlight, reducing photosynthesis and thus draining the sea of nutrients. Bigger organisms that processed more water had a better chance of eating enough to survive. Once the glaciers melted, these larger organisms could expand further.
The model reflects the latest paleontological research, building on work by two additional co-authors, former SFI Omidyar Postdoctoral Fellow Jack Shaw and Carl Simpson, a scientist at the University of Colorado, Boulder.
“Our study offers hypotheses of ancestor organism features to hunt for in the fossil record,” says Crockett.
The paper also presents new tools for investigating physical effects on organism physiology, a boon for future research.
“We provide a useful framework for people to interpret Earth’s past, understand modern ecology, and study organism physiology in the lab,” says Kempes.
Reference: “Physical constraints during Snowball Earth drive the evolution of multicellularity” by William W. Crockett, Jack O. Shaw, Carl Simpson and Christopher P. Kempes, 26 June 2024, Proceedings of the Royal Society B.
DOI: 10.1098/rspb.2023.2767
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3 Comments
“But the oxygen story doesn’t fully explain why multicellular ancestors of animals, plants, and fungi appeared simultaneously, …”
Why not? Air gets everywhere on Earth, even places that little or no water gets to.
This is a novel bedtime story, but I don’t think that the argument is compelling. It seems to be ‘supported’ by assumptions and assertions that are based on little more than the authors wanting it to be true.
Earth’s material history has nothing to do with the arrival of one man and one woman. Before these. All life was created and snowball theory is bogus just as evolution is bogus. None is replicable nor ever observed.
“Earth’s material history has nothing to do with the arrival of one man and one woman.”
First of all, it is illogical to assert without evidence ‘the arrival of one man and one woman’. But even allowing for that, your logic is still flawed – at minimum, the earth would have to be created to host those two.
“Before these.”
This is not even a complete sentence.
“All life was created and snowball theory is bogus just as evolution is bogus. None is replicable nor ever observed.”
You can scream your opinions all you want, but opinions without supporting arguments have no place in intelligent human conversation. Where is your evidence for all that you claim? Especially the theory of evolution is quite old, and a bunch of scientists have presented a bunch of evidence to support that theory, and so the onus is on you to start there and show why all those scientists are wrong. Just stating your opinion is ok, if that’s all you can do, but then don’t expect others to take you seriously.