‘Snowball Earth’ helps explain the origin of complex life

Biological life made the leap from simple, one-celled microbes to complex multi-cellular plants and animals following a period of glaciation that began around 700 million years ago, geologists from the Australian National University reported online Wednesday in the journal Nature.

Scientists have long searched for the potential catalyst in the evolution of complex life, and now, lead author Jochen J. Brocks and his colleagues have discovered that the same conditions that led to the phenomenon known as “snowball Earth” may have also led to multi-cellular organisms.

Approximately 700 million years ago, the Earth was almost entirely covered in snow following an event known as the Sturtian glaciation, Ars Technica explained. That period lasted around 50 million years and was followed by an intense period of heating that lasted for around 15 million years before giving way to another period of glaciation.

It was during the 15 million year period between ice ages that Brocks and his colleagues believe that multi-cellular life began to emerge, as dust from huge mountain ranges that were pulverized during the Sturtian glaciation found its way into newly formed oceans, providing nutrients which allowed blue algae to thrive and essentially kick-starting the evolutionary process.

Those nutrients, along with the period of global cooling that followed, provided ideal conditions for the algae to thrive, Brocks explained in a statement. As the algae spread, it marked the end of the dominance of ocean-based bacteria and the start of the transition to more complex life.

How the glaciation causes changes that led to multi-cellular organisms

The study authors based their claims on an analysis of ancient sedimentary rocks that they found in central Australia and pulverized into a powder, which enabled them to extract the molecules of ancient organisms. Their analysis revealed the significant effect that “Snowball Earth” had on the ecosystem, suggesting that it served as a catalyst for the rise of multi-cellular organisms.

“These large and nutritious organisms at the base of the food web provided the burst of energy required for the evolution of complex ecosystems,” Brocks explained in a press release, “where increasingly large and complex animals, including humans, could thrive on Earth.”

He and his colleagues identified traces left behind by cell membranes in those rocks, noted Ars Technica. Specifically, they found that chemical changes in these biomarkers revealed the rapid increase of larger organisms in the post-Snowball Earth oceans – including eukaryotes that had developed a nucleus. That is a key development in the rise of multi-cellular life, they said.

Of course, such organisms could not develop without changes to the ecosystem after the end of the Sturtian glaciation, and those molecular changes came about as a result of the nutrients that made their way into the water thanks to rocks from mountains which eroded during the ice age. Those nutrients would have plummeted to the bottom of the sea, which resulted in a release of oxygen into the atmosphere and set off a chain of events that led to the rise of complex life.

“The rise of oxygen…very likely led to the rise of phosphorous in the water, which is a key building block in DNA, and the energy-rich molecule ATP that provides fuel for our bodies,” said Ars Technica. This led to the proliferation of algae, then to the evolution of lifeforms that used said algae for food. Those changes persisted even after the Minoan glaciation once again covered the world in ice, and when the climate eventually stabilized, it facilitated the evolution of animals with heads and internal organs, the website explained.


Image credit: NASA