The Earth was a hostile environment marked by unpredictable climate and oxygen-deprived air over 3 billion years ago. Researchers of a new study, however, have claimed that regardless of these conditions, life was able to thrive on our planet during this period.
For the study, which was published in the journal Nature on Feb. 16, Roger Buick from the Department of Earth & Space Sciences and Astrobiology Program of the University of Washington, together with colleagues, analyzed some of the oldest and best-preserved rocks that were collected in northwestern Australia and South Africa.
The 52 rock samples that the researchers looked at date back from between 2.75 billion to 3.2 billion years ago and were formed before oxygen became present in the atmosphere and thus preserved the chemical clues that are not present in modern rocks.
The researchers found that there were plenty of nitrogen 3.2 billion years ago that would have sustained the most basic life forms such as viruses, bacteria and other organisms, suggesting that organisms that can pull nitrogen from the atmosphere and convert this into a usable form first emerged during this period, which is a billion years earlier than previously believed.
Early life forms may have thrived without oxygen as this was not present in the atmosphere until the so-called "great oxygenation event" that occurred 2.3 billion years ago. These life forms, however, required a type of nitrogen, found in the ancient samples of rock, for building genes and for other important life processes.
The rock samples contain chemical signatures that show nitrogen was broken by an enzyme based on molybdenum, one of the three nitrogen-fixing enzymes that currently exist.
"Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event," the researchers wrote.
The researchers likewise said that the early organisms may have crawled out of the ocean and thrived on land in a single layer of cells, noting that the chemical reaction that was preserved in the rock samples indicate that they only happen in the presence of life.
"We'll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited," Buick said, adding that microbes could have lived on the rocks even earlier than 3.2 billion years ago.