A new study found that in a short period of 2 billion 300 million years ago, the early earth had an oxygen enriched atmosphere. This supports the theory that complex life, including animal like organisms, may have evolved on earth.
In our ancestors first roamed the earth for billions of years before, the so-called Lomagundi event (from 23 to 2 billion 100 million years ago, the enrichment of C-13 limestone and dolomite in the world) may provide a brief opportunity for complex biological animal like evolution.
Scientists believe that about 4 billion years ago, life first appeared on earth. However, it was not until 3 billion years later that eukaryotes appeared on earth.
But there is also evidence that in the early Proterozoic (from 25 to 1 billion 600 million years ago) the great oxidation event (Great Oxidation Event) the early earth had enriched period, this is the Lomagundi event, which occurred in about 23 to 2 billion 100 million years ago. Scientists want to know if the oxygen rich environment at that time was sufficient to support the evolution of higher forms of life, and if so, why did not occur in this period of time, but after one billion years.
A team at the University of Washington (University of Washington) has examined the chemical composition of Lomagundi rocks, and the results show that the number of organic carbon buried deep in the ocean has suddenly increased. The abundance of selenium and the ratio of Se/TOC (total organic carbon) also showed a significant increase in oxygen content during the Lomagundi event.
The presence of selenium indicates that oxygen is contained in the atmosphere, because when the rock is eroded in the presence of a gas, it releases selenium, which is then carried into the ocean, where it slowly deposits on the ocean floor.
However, scientists have not yet reached a consensus on why the early earth had been briefly obtained and then lost its oxygen enriched atmosphere. Now, in order to better understand the oxygen content during the Lomagundi event, the University of Washington research team analyzed the selenium isotope ratio during the formation of the rock in the sea, and then estimate the level of dissolved oxygen in shallow wate.
The study found that the oxygen content was high enough to support life, and even the life of an animal. Scientists describe this period as a "time oxygen oasis."".
Calculation shows that the research team, the level of dissolved oxygen in shallow water is about 5 mol per liter of water, the level is far less than 325 micromoles per liter of water. However, this figure is higher than the hypoxia today many simple marine animal needs 0.9 micromoles per liter of water. Therefore, the level of oxygen was sufficient to support the evolution of more complex life, scientists have to do is to find the evidence.
source：http://tech.163.com/17/0123/11/CBF99V2000097U81.html