Study shows continental crust emerged 500 million years before previously thought

Researchers have published a new study that found the continental crust on Earth emerged 500 million years earlier than previously believed. According to the team, the first emergence and persistence of continental crust on Earth during the Archaean between 4 billion and 2.5 billion years ago has implications for plate tectonics, ocean chemistry, and biological evolution. Researchers note that the emergence of the continental crust happened about half a billion years earlier than previously believed.

Scientists note that when land becomes established through dynamic processes such as plate tectonics, the land begins to weather and add minerals and nutrients to the ocean. A record of those nutrients is preserved in ancient rock. Previously, researchers used strontium isotopes in marine carbonates, but those rocks are usually scarce or altered when more than 3 billion years old.

The researchers have a new approach to trace the first emergence of old rocks using a different mineral called barite. Barite forms when sulfite from ocean water mixes with barium from hydrothermal vents. Barite maintains a record of ocean chemistry within its structure which is useful for reconstructing ancient environments. Scientists on the project picked up a piece of barite in the field that has been on Earth for 3.5 billion years that is exactly the same as it was when it first precipitated.

The team tested six different deposits on three different continents ranging from 3.2 million to 3.5 billion years old. The team calculated the ratio of strontium isotopes in the barite and was able to infer the time when the weathered continental rock made its way to the ocean and incorporated itself into the barite.

The team found weathering started about 3.7 billion years ago, about 500 million years earlier than previously thought. Researchers say the discovery has implications for the way we think about how life evolved.