A study by scientists at the University of Washington (USA) showed that conditions suitable for the emergence of life on our planet arose a billion years before the first living organisms appeared. The study's lead author, Michael Kipp, used selenium in sedimentary ancients to determine the oxygen content of the Earth's atmosphere.
"There is fossil evidence of complex cells that are 1.75 billion years old," says Roger Buick, one of the study's co-authors. "But these fossils might not have preserved the oldest organisms, since the chances of being preserved as fossils are generally very low."
“The study shows that there was enough oxygen in the environment to allow complex cells to appear,” he continued. "This means that life could have existed even then."
The researchers found that a billion years before life arose, an atmosphere with a fairly high level of oxygen appeared on Earth. During this period, all the conditions for the existence of living organisms developed on the planet. This period lasted for about 250 million years, after which the oxygen content in the air dropped sharply, making the existence of living things impossible. And only after more than 700 million years, the oxygen level began to rise again.
What caused such fluctuations in the concentration of oxygen in the air remains to be seen by scientists.