An article published in the journal “Nature” describes a research that provides an explanation for the rise of animals on Earth. According to a team of researchers led by the Australian National University (ANU), animals evolved at the height of a series of events. There was the end of the glacial period known as Snowball Earth and the spread of algae, which became together with simple substances a crucial source of nutrients that allowed more complex organisms to emerge.
For most of the history of life on Earth organisms have been unicellular but at some point more complex organisms started appearing. After hundreds of millions of years it’s difficult to reconstruct those phases of evolution. The appearance of animals profoundly affected Earth’s life but the shortage of fossils of that remote era makes it difficult to analyze that event.
The international team that included researchers from the ANU, the Max Planck Institute for Biogeochemistry and the University of Bremen in Germany led by Professor Jochen Brocks of the ANU studied traces of ancient organisms to try to understand the reasons for the rise of animals. These researchers found something interesting about 650 million years ago, the rise of algae.
The geological period considered for this research is the Cryogenian, between 720 to 635 million years ago. It includes the Sturtian and Marinoan glaciations, epochs where according to a part of the researchers ice covered the whole planet and turned it into what is called “Snowball Earth”. The possible influence of these glaciations on animal evolution has long been the subject of discussion and according to Jochen Brocks’ team the answer is positive.
According to the researchers, the Sturtian glaciation had profound effects on the environment, also because the glaciers in their movements pulverized entire mountains releasing many simple substances that, at the end of glaciation, ended up in the seas, transported by rivers. Along with rising temperatures, the presence of these substances allowed the algae to proliferate because many of them were nutritious.
That proliferation represented a major shift from the oceans’ domain from bacteria to that of more complex organisms. It was a crucial change because it created a new kind of ecosystem in which there were not only simple nutrients but also algae, a food that could provide a greater amount of energy.
Those algae didn’t leave fossils so the researchers had to look for other traces. Specifically, by analyzing sedimentary rocks from that time they found the remains of the molecules left by algae. The examination shows the proliferation of algae, ideal for organisms that could eat them to evolve: animals.
Perhaps the first animals were sponges but that’s the subject of discussion because various researches point to it but there are those who claim that the first animals were actually the gelatinous ctenophores. This new research says nothing about this topic but offers new ideas about the rise of animals. Discussions have already started and will probably continue for a long time because data are limited and this makes their interpretation difficult.