Several tens of millions of years before the so-called Cambrian expansion, Earth experienced a breakthrough, the lesser-known Avalon explosion. Until now, scientists believed that what allowed life to make its way was oxygen.. Now they have to rethink this idea.
The first 2 billion years of life on Earth were dominated by single-celled organisms. Something happened later. Life began to become more complex and things began to emerge. multicellular organisms like sponges.
During the last seven decadesthe scientific consensus has been based on the idea that between approximately 685 and 800 million years ago they began to appear the first multicellular organisms thanks to a relevant change on our planet: an increase in oxygen levels.
This time of increase in the level of oxygen would have been the one that would have laid the foundations for the first expansion of life on Earth, the avalon explosionwhich occurred about 575 million years ago, about 30 million years before the cambrian expansionthe one that laid the foundations of life as we know it.
The expansion of Avalon would have had a great impact on animal life as well. The bilateral animals (a group that includes most animals, from annelids to mammals, through molluscs or insects) would have evolved in this period. But this revolution would not have been possible without the appearance of the first multicellular organisms in earlier geological periods. And this, according to what was believed to be known until now, was only possible thanks to an increase in oxygen levels in the Earth’s waters.
An international team of researchers just found a problem with this narrative, and it is that, after carrying out a geological analysis with rocks of the time, they did not find no trace of this alleged increase in oxygen levels. Now the question of what induced this explosion of life has been reopened.
“Our measurements provide a good picture of what the average oxygen concentrations were in the world’s oceans at that time. And it is apparent to us that there was no great increase in the amount of oxygen when the more highly evolved fauna began to evolve and dominate the Earth. In fact, there was something like a slight reduction.” points out Christian J. Bjerrumone of the authors of the new study.
For your study, Bjerrum and the rest of the team studied sedimentary rocks from the mountain range in northern Oman. Studying the sediment strata corresponding to the time, specifically looking at isotopes of thallium and uraniumfound that the seabed at the time did not contain as much oxygen as might be expected.
The study also incorporated contemporary samples taken elsewhere, specifically in the Mackenzie Mountains of Canada and the Yangtze Gorge in China.
But then, if it wasn’t the abundance of oxygen that set the stage for the first great expansion of life, what happened? It is not possible to know for now, the team responsible for the study has a hypothesis: if it was not the abundance, perhaps it was the lack.
“It is interesting that the explosion of multicellular organisms occurs at a time with low atmospheric and oceanic oxygen concentrations. That indicates that organisms benefited from lower oxygen levels and they were able to thrive in peace, as the chemistry of the water naturally protected their stem cells.”
Bjerrum refers to a phenomenon observed in the context of the investigation of some cancers. As he explains, low oxygen levels allow stem cells to be kept under control until it is time for them to convert into a specialized or mature cell. According to this hypothesis, the lack of oxygen would slow down the maturation process, reducing the number of mutations in the cell and thus allowing a slower but surer development.
The link between oxygen and life as we conceive it is undeniable. So much so that the idea that a lack of oxygen could lay the foundations for life on Earth is counterintuitive. However, very little is known about the beginnings of life and the geochemical conditions of our planet hundreds of billions of years ago. What we do know is that the clues to decipher the enigma are written in stone.
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Image | Albert Kok