2021-04-28

The continental crust appeared 500 million years earlier than previously thought

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The continental crust appeared 500 million years earlier than previously thought

According to the British “New Scientist” magazine, the earth was a lava hell when it formed 4.5 billion years ago. Eventually the outer layer of the earth A solid crust covered by the ocean. Once the terrestrial crust is formed, it begins to weather and transport important minerals and nutrients to the ocean. This process is crucial to the birth of the original life, and the traces of these nutrients are preserved in ancient rock records.

In the past, scientists used strontium isotopes in ocean carbonates when inferring the formation of the earth’s continents, but rocks with a history of more than 3 billion years are rare and prone to alteration. In view of this, the researchers took a different approach and used barite to infer when the earth’s continents formed.

Barite is a mixture of sulfate in seawater and barium ejected from hydrothermal vents. It preserves a wealth of ocean chemical records and helps to reconstruct the ancient environment. Desiree Roldink, a geochemist at the University of Bergen in Norway, explained: “Barites will not really change. Their chemical composition contains the’fingerprint’ of the environment in which they are formed.”

The continental crust appeared 500 million years earlier than previously thought(1)

Thirty ancient rock samples from 6 locations were analyzed, and these samples all contained barite. They calculated the proportion of strontium isotopes in barite and inferred the time when weathered continental rocks entered the ocean and entered the barite. They found that weathering began about 3.7 billion years ago, earlier than previously thought. About 500 million years.

Roldink said: “This is a very long period of time, which is of great significance for us to think about how life evolved. Scientists usually believe that life begins in the deep sea, but the biosphere is very complicated. We don’t know. Is it possible for life to evolve at the same time on land?”

Aaron Satkowski of the University of Texas at Austin said that the new research results indicate that life may have started on land as early as possible. Not in the ocean.