It is believed that the emergence of complex multicellular organisms is a unique event in Earth’s history happened only once. It was about 1.6–1.7 billion years ago when bacteria and archaea that lived on the planet for almost 2 billion years old, joined the first eukaryotes, which later evolved animals and plants, fungi and protists. This period was no coincidence that the key: just then, the oceans have accumulated enough oxygen.
Complex mechanisms of protection from oxidative stress, a complex system of use for cellular respiration in the mitochondrial membranes – all this began to bring greater returns. Archean absorbed but not digested random bacteria could develop in the mitochondria and the whole cell is eukaryotic. About 800 million years ago when oxygen filled atmosphere, and the air got almost contemporary composition, the Earth was already dominated by complex multicellular organisms.
However, Michael Kipp (Michael Kipp) and his colleagues at Washington University have concluded that oxygen on Earth was quite before. Between 2.1 and 2.3 billion years ago, its level has been raised for some inexplicable reason, and then mysteriously dropped again. This period could occur and reproduce, others multicellular, and then completely dying and not leaving any traces in the ancient fossils. This researchers write in the article, published in the journal PNAS.
The authors investigated the content of selenium in sedimentary rocks that are dated two or more billion years ago. It metaboliziruet methanogenic microbes of the sea bottom, gradually changing the ratio of the isotope selenium-82 and 78. However, the speed of this process depends on the presence of oxygen that allows you to use the selenium analysis for the evaluation of the content of this oxidizer.
These data and pointed to the sudden (and as suddenly disappeared) peak oxygen content in the ocean between 2.1 and 2.3 billion years ago. It reached 5 mmol/l, which is considerably below the modern 325 µmol/l, but still significantly above the minimum, which is sufficient to many modern inhabitants of the sea (about 0.9 mmol/l). This is not the first such finding. Some previous work has also found traces of a mysterious burst of oxygen in earth’s oceans at the time – Lomagundi-Adolesce event. Its cause remains unknown.
One of the authors of the new Roger Buick (Roger Buick) explains: “Our study shows that oxygen in the environment then it is sufficient for the development of complex cells, in order to have significant ecological value earlier than indicated by fossil remains. This does not mean that the way it was, but the possibility is there”.