Two billion years ago, bacteria were the dominant species on Earth. Yet at some point in the last half a billion years, life evolved into multicellular organisms. Scientists now believe they’ve finally uncovered the details of this monumental change.
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There have been many differing theories about the beginning of this evolution, but a team from the Australian National University (ANU) have just made a discovery that could finally provide some answers as to the when and why. And it all began when the Earth was a giant snowball.
Our planet underwent an extreme ice age around 717 million years ago, known as the the Sturtian glaciation. It’s aso informally called the time of “Snowball Earth”, for the ice that covered the planet from poles to equator, and lasted around 50 million years. That ice age ended 659 million years, with an intense greenhouse period where Earth warmed rapidly. However, just as that warmth was peaking, we were hit with the Marinoan glaciation, which covered the planet in ice once more. By analyzing chemical traces of life in rocks up to a billion years old, the ANU team believe they’ve discovered how that short span between the two ice ages may have led to the evolutionary tipping point.
Called the “rise of the algae”, the research evidence shows the time period saw a rapid rise of marine planktonic algae.
“The Earth was frozen over for 50 million years,” explains lead researcher Jochen J 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.”
Ice Age
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Not just that, but the melting ice also ended up burying huge reserves of naturally occurring carbon undersea, which scientists also believe resulted in an equivalent net worth of oxygen being released into the water and air.That rise in oxygen likely also led to a rise of the phosphorus levels in water, a key component in DNA, and the energy-rich molecule ATP that provides fuel for our bodies.
With the oceans suddenly rich in nutrients, new algae evolved and thrived, allowing larger and more complex organisms to evolve as well. “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.
What’s most interesting though, is that the second ice age didn’t reverse this process. The Marinoan glaciation ended 635 million years ago, approximately 15 million years after the previous ice age, which is the when we can track some of the oldest multicellular organisms.