Science

How "Snowball Earth" led to the evolution of complex life

"Snowball Earth" appears to have led to an explosion in algae growth
"Snowball Earth" appears to have led to an explosion in algae growth
View 3 Images
Associate Professor Jochen Brocks and Dr Amber Jarrett
1/3
Associate Professor Jochen Brocks and Dr Amber Jarrett
From the crushed up sedimentary rocks the team were able to identify specific molecules
2/3
From the crushed up sedimentary rocks the team were able to identify specific molecules
"Snowball Earth" appears to have led to an explosion in algae growth
3/3
"Snowball Earth" appears to have led to an explosion in algae growth

For billions of years bacteria dominated the globe, but at some point a major transition occurred and complex multicellular life began to take hold. The when and why of this transition has been the source of great debate for years, but a team at the Australian National University (ANU) has made a discovery that could finally answer those questions – and it takes us all the way back to a time when the Earth was a giant snowball.

An extreme ice age hit the planet around 717 million years ago. Known as the Sturtian glaciation, this event is more informally dubbed "Snowball Earth" and it's thought to be the most extreme, and long-lasting, ice age the planet ever experienced. For around 50 million years, the entire globe was essentially covered in ice.

In between the Sturtian glaciation and the planet's next, but much shorter, glaciation event there was a small stretch of around 15 million years. It is this relatively short time frame that scientists from ANU are now calling the "rise of the algae", with evidence showing the time period signaled a rapid rise of marine planktonic algae.

But what happened in this small window of time to cause such a dramatic ecological shift on the planet?

"The Earth was frozen over for 50 million years," explains lead research Jochen Brocks. "Huge glaciers ground entire mountain ranges to powder that released nutrients, and when the snow melted during an extreme global heating event rivers washed torrents of nutrients into the ocean."

Associate Professor Jochen Brocks and Dr Amber Jarrett
Associate Professor Jochen Brocks and Dr Amber Jarrett

As the oceans were suddenly fueled with such high levels of nutrients, the perfect conditions appeared for algae to thrive. The ANU research tracked this explosion in new algae by studying ancient sedimentary rocks found in Central Australia.

"We crushed these rocks to powder and extracted molecules of ancient organisms from them," says Dr Brocks.

The explosion in algae growth during this window of time is now thought to be the major trigger that allowed larger and more complex life forms to evolve. The study notes that the timing of this algae explosion explains the concomitant appearance of complex predatory rhizarians and sponges.

From the crushed up sedimentary rocks the team were able to identify specific molecules
From the crushed up sedimentary rocks the team were able to identify specific molecules

"These large and nutritious organisms at the base of the food web provided the burst of energy required for the evolution of complex ecosystems, where increasingly large and complex animals, including humans, could thrive on Earth," says Dr Brocks.

Interestingly, the next glaciation period, the Marinoan glaciation, didn't reverse this remarkable step forward. Lasting an estimated 15 million years, the Marinoan glaciation ended approximately 635 million years ago, marking the beginning of the Ediacaran period, where we can track the oldest multicellular organisms.

This new ANU research explaining the "rise of the algae" fills a gap in our knowledge, offering strong evidence to explain the subsequent growth of complex lifeforms on our planet. It's undoubtedly a striking, and ground-breaking, discovery that shows how the most dramatic ice age the planet has ever seen directly triggered a process that led to the evolution of complex life.

The research was published in the journal Nature.

Source: Australian National University

7 comments
Bob Stuart
Multicellular life may also have been waiting for the background radiation to go through many half-lives.
Jose Gros
One of the possible ends of planet Earth may be transient. If we survive the 'Global warming', the Sun is slowly but surely increasing its radiation, sooner or later, the temperatures on Earth will be too hot for life, then, the Sun will change into a Red Giant, engulfing Earth's orbit inside its atmosphere; if drag doesn't send planet Earth down towards the Sun, the Red Giant phase is transient, and gives place to a 'White dwarf', or neutron star, that can last billions of years. If under the light of the neutron star, a surviving Earth would have a surface temperature compatible with life, somebody who comes in will find one of the longer lasting homelands in the universe, as the crust contains water to replenish oceans several times. Earth girls are easy!
Readout Noise
Jose: "'White dwarf', or neutron star, that can last billions of years." The Sun will not become a neutron star - it is not massive enough. It will become a white dwarf. And a white dwarf generates no energy: it just gradually cools and radiates away the heat it was born with, which means that the habitable zone (HZ) around it is constantly shrinking inwards - the HZ doesn't stay around any surviving planet for long. Very soon, the output from the white dwarf becomes too feeble to sustain any nearby life.
Bob
So, global warming isn't such a bad thing.
piperTom
Thus the Snowball Event may qualify as one the gateways that explain the Fermi Paradox. Life could be common in the Milky Way and still allow for complex life to be uncommon.
VincentWolf
Better to be hot and stay in caves to stay cool (coming out when it's cool at night) than to be frozen to death in an iceball Earth.
CharlieSeattle
717 million years ago, the map of the Earth before the Pre-Cambrian era even before Pangea was much different than Modern Continents shown above.
Thanks for reading our articles. Please consider subscribing to New Atlas Plus.
By doing so you will be supporting independent journalism, plus you will get the benefits of a faster, ad-free experience.