A global ice age known as “Snowball Earth” triggered the development of complex life 650 million years ago, new evidence suggests.
Scientists believe glaciers covered the planet and pounded entire mountain ranges to powder, releasing life-sustaining nutrients.
When the snow and ice finally melted, the nutrients were washed into the oceans to fuel the rapid development of algae.
The primitive photosynthesising plant organisms marked the transition from aeons of bacterial life to complex ecology and multitudes of animal species.
Without this first step, humans would never have existed on Earth, it is claimed.
Scientists say they have solved the mystery of how complex life first appeared on Earth after analysing very ancient sedimentary rocks from central Australia.
Dr Jochen Brocks, from the Australian National University (ANU), said: “We crushed these rocks to powder and extracted molecules of ancient organisms from them.
“These molecules tell us that it really became interesting 650 million years ago. It was a revolution of ecosystems, it was the rise of algae.”
The change was linked to a destiny-shaping event 50 million years earlier when virtually the entire planet was covered in glaciers and ice sheets.
The Snowball Earth theory is controversial, but has been supported by the discovery of glacial deposits in tropical regions.
“The Earth was frozen over for 50 million years,” said Dr 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.”
This created the perfect conditions for the evolution and spread of algae, which in turn provided a food source for higher forms of life.
Dr Brocks added: “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.”
The findings will also be presented to geochemistry experts at the Goldschmidt Conference in Paris, France, this week.
Co-author Dr Amber Jarrett, also from the ANU, said the rocks studied provided “striking signals” of molecular fossils dating back to just after the great Snowball Earth thaw.
“We immediately knew that we had made a ground-breaking discovery that Snowball Earth was directly involved in the evolution of large and complex life,” she said.
The research is published in the journal Nature.