A spike in the chromium contained in ancient rock deposits, laid down nearly 2.5 billion years ago, reveals what appears to be the earliest evidence for oxygen-breathing life on land.
The transformation known as the Great Oxidation Event occurred when the atmosphere gained oxygen, an element crucial for nearly all animal life, including humans. The new analysis indicates the earliest estimate to date for the start of the Great Oxidation Event — 2.48 billion years ago. Other research has suggested small amounts of the gas appeared in the oceans and possibly the atmosphere around 2.5 billion years ago.
For this study, the researchers performed more than 2,000 analyses on samples from more than 100 rock formations, including those called banded iron formations, located around the world, from Canada to South Africa.
Primary source: Nature