Earth’s early evolution: fresh insights from rocks formed 3.5 billion years ago Premium

Evidence is preserved in ancient volcanic and sedimentary rocks dating back to the Archaean age, between 4 billion and 2.5 billion years ago.

Our Earth is around 4.5 billion years old. Way back in its earliest years, vast oceans dominated. There were frequent volcanic eruptions and, because there was no free oxygen in the atmosphere, there was no ozone layer. It was a dynamic and evolving planet.

Scientists know all of this – but, of course, there are still gaps in our knowledge. For instance, while we know what kind of rocks were being formed on different parts of the planet 3.5 billion years ago, we are still understanding which geological processes drove these formations.

Luckily the answers to such questions are available. Evidence is preserved in ancient volcanic and sedimentary rocks dating back to the Archaean age, between 4 billion and 2.5 billion years ago.

These rocks are found in the oldest parts of what are today the continents, called cratons. Cratons are pieces of ancient continents that formed billions of years ago. Studying them offers a window into how processes within and on the surface of Earth operated in the past. They host a variety of different groups of rocks, including greenstones and granites.

One example is the Singhbhum Craton, in the Daitari Greenstone Belt in the state of Odisha in eastern India. This ancient part of the Earth’s crust has been found in previous research to date back to 3.5 billion years ago. The craton’s oldest rock assemblages are largely volcanic and sedimentary rocks also known as greenstone successions. Greenstones are rock assemblages made up mostly of sub-marine volcanic rocks with minor sedimentary rocks.

My research team and I recently published a study in which we compared the Singhbhum Craton to cratons in South Africa and Australia. We chose these sites because they preserve the same kinds of rocks, in the same condition (not intensely deformed or metamorphosed), from the same time period – about 3.5 billion years ago. They are the best archives to study early Earth surface processes.

Our key findings were that explosive-style volcanic eruptions were common in what are today India, South Africa and Australia around 3.5 billion years ago. These eruptions mostly occurred under oceans, though sometimes above them.