October 19, 2013
Pre-Cambrian Explosion Oxygen Levels Raise Evolutionary Questions
redOrbit Staff & Wire Reports - Your Universe Online
An international team of researchers has discovered that the Earth’s oxygen content 2.1 billion years ago was the same as it was during the so-called Cambrian explosion that occurred approximately 542 years ago and resulted in the appearance of most major animal phyla.
One possible explanation, they explain in the journal Proceedings of the National Academy of Sciences, is the fact that most traces of advanced life that existed two billion years ago has since disappeared. If those creatures failed to develop shells or skeletons, they would not have been easily fossilized and it would be unlikely that experts would find their remains today.
While bacteria and other simple organisms can survive without oxygen, nearly all advanced organisms require the element, the investigators said. Without the 21 percent currently found in our planet’s atmosphere, the biodiversity of the planet would suffer, as the human brain and other vital systems would not be able to function.
During the Cambrian explosion, the atmospheric oxygen levels increased by up to 10 percent, and prior to that time the living creatures roaming the Earth were typically small, simple and often single-celled. Scientists had long assumed that there simply was not enough oxygen for creatures to evolve into higher species, but now the study authors demonstrate that the element had previously been abundant enough to support advanced systems.
“We have examined rocks that are 2.15 billion - 2.08 billion years old. They show us that there was oxygen in deep water and thus also in the atmosphere at that time,” Emma Hammarlund, a post-doctoral researcher from the Nordic Center for Earth Evolution (NordCEE) at University of Southern Denmark, said in a statement. “We cannot say exactly how much, but there was probably ample oxygen and also ample time to permit advanced life to evolve.”
Working on the research alongside Hammarlund was NordCEE professor Donald Canfield, as well as associates from the National Museum in Sweden and the Université de Poitiers, the Centre National de la Recherche Scientifique, the Institut Francais de la Recherche pour l' Exploitation de la Mer, Centre de Brest and the Université de Rennes in France.
Hammarlund and her colleagues previously discovered unusual fossils that they believed are indicative of a way of life which attempted to evolve into a multicellular life form. This life form, she said, “was not a life form that in any way is comparable to large life as we know it today. It was rather microbes that experimented with a way to evolve into some form of multicellular existence. It had enough oxygen for the experiment, but its destiny is unknown.”
The failure of two billion year old advanced life forms to develop protective shells or bones, thus inhibiting their ability to become fossilized and discovered today, could explain why there is no evidence of the existence of these entities. While that is possible, Hammarlund said that her team currently considers it “more likely” that no evolutionary explosion took place during that era, despite the elevated oxygen levels.
“But why not, since there was plenty of oxygen? Perhaps the problem was with the genetics of the life forms,” she explained. “Or maybe the organisms did not try to eat each other, so an evolutionary race could get started. There are several options, but we just do not know enough about it yet.”