Fossil and molecular evidence suggests that complex multicellular organisms arose and proliferated during the Neoproterozoic Era (1-541 million years ago). An extreme glacial period during the Cryogenian Period (720-635 million years ago), an event commonly referred to as Snowball Earth, led to dramatic changes in Earth's climate and oceans. New research suggests that Snowball Earth was an environmental trigger for the proliferation of complex multicellularity across multiple groups of eukaryotic organisms.
Artist's impression of “Snowball Earth.” Image courtesy of NASA.
Solving the mystery of why multicellular organisms emerged could help pinpoint life on other planets and explain the enormous diversity and complexity seen on Earth today, from marine sponges to redwoods to human societies.
The prevailing thinking is that oxygen levels must reach a certain threshold for a single cell to form a multicellular colony.
However, the oxygen story does not fully explain why the multicellular ancestors of animals, plants and fungi emerged simultaneously, or why the transition to multicellularity took more than a billion years.
The new study shows how the specific physical conditions of Snowball Earth, particularly the viscosity of the oceans and the depletion of resources, may have led eukaryotes to become multicellular.
“It seems almost counterintuitive that these extremely harsh conditions – this frozen planet – could actually select for larger, more complex organisms, rather than causing species to become extinct or shrink in size,” said William Crockett, a doctoral student at MIT.
Using scaling theory, Crockett and his colleagues found that a hypothetical ancestor of early animals, reminiscent of swimming algae that fed on prey instead of photosynthesizing, would have grown in size and complexity under Snowball Earth pressures.
In contrast, single-celled organisms that move and feed by diffusion, such as bacteria, will grow small.
“The world changed after Snowball Earth because new life forms emerged on the planet,” said Professor Christopher Kemps of the Santa Fe Institute.
“One of the central questions of evolution is: How did we evolve from nothing on Earth to beings and societies like us? Was it all by chance?”
“We don't think it's luck. There are ways to predict these big changes.”
The study shows how, during the Snowball Earth era, the oceans froze, blocking sunlight and reducing photosynthesis, which resulted in nutrient depletion in the oceans.
Larger organisms that could process more water were more likely to eat enough to survive.
As the glaciers melt, these large creatures could expand even further.
“Our study provides hypotheses about ancestral features to look for in the fossil record,” Crockett said.
of study Published in Proceedings of the Royal Society B.
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William W. Crockett others2024. Snowball Earth's physical constraints drive the evolution of multicellularity. Proc. R. Soc. B 291 (2025): 20232767; doi: 10.1098/rspb.2023.2767
This article is a version of a press release provided by the Santa Fe Institute.
Source: www.sci.news
