Super ice age made biodiversity possible
For a billion years, the ancestors of plants and animals formed only a few new forms. But then a global catastrophe struck - and unleashed evolution.
Simple single-celled organisms such as bacteria may be the most successful creatures on earth, but our own relatives offer the greatest diversity of forms: the eukaryotes, organisms with a cell nucleus that were the only ones to give rise to multicellular organisms. From birds that spend almost their entire lives in the air, to millennia-old clone colonies, to the unrivalled mega-structures of reef-building corals. We owe this immense wealth of forms primarily to a super ice age. This is the conclusion reached by a research group led by Qing Tang from Nanjing University after a comprehensive analysis of the evolution of our oldest ancestors. As the team reports in the journal "Science", the evolution of multicellular organisms changed dramatically after the Cryogenian glaciation epoch around 650 million years ago - from leisurely and stable to erratic and radical.
Multicellular life forms have probably existed for around 1.8 billion years. But for most of this time, they didn't do too much. New forms emerged from time to time, but their diversity, measured in terms of the number of species and families, remained constant and relatively low for around a billion years. Until an unimaginable global catastrophe struck: Snowball Earth. This is the name given to a period around 720 million years ago when almost the entire Earth froze over. For 70 million years, ice sheets covered the Earth's continents and the oceans almost completely froze over. It was an apocalypse for large parts of life on earth. For the simple multicellular creatures from which we also descended, however, the extreme climate proved to be a stroke of luck.
Because the global crisis put an end to evolutionary inertia. Diversity and the rate at which new species emerged increased dramatically. It all started with the unicellular eukaryotes, whose number of species tripled by leaps and bounds - and collapsed after another ice age 580 million years ago. But this glaciation was the starting signal for the first animals. It all started with the still mysterious creatures of the Ediacara fauna. Again and again, new species emerged in radical spurts and disappeared again dozens of times in equally dramatic episodes, paving the way for new episodes of evolutionary creativity. The evolution of multicellular organisms, unspectacular for a billion years, had become a rollercoaster ride of life. It culminated 520 million years ago in another unprecedented surge of speciation - known as the Cambrian explosion. This was when the precursors of our current animal groups first appeared.
Spectrum of Science
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