Science 3 min read

What "Komatiites" Tell us About Earth's History

Geochemical analysis of komatiites, ancient volcanic rocks, reveal that the process by which our planet recycles matter, particularly water, is much older than we thought.

Image courtesy of Shutterstuck

Image courtesy of Shutterstuck

Though regarded as one of nature’s most destructive forces, volcanoes played a critical role in the development of life on Earth.

Besides the formation of the land itself, volcanic eruptions helped release the water molecules trapped deep into the mantle; first, water dissolves in the magma before it gets spewed out by the volcano. Then, when it reaches the surface, the now-called lava emits water as vapor due to the reducing pressure.

While another theory attributes the existence of liquid water on Earth to comets, recent studies, however, make scientists lean more toward volcanoes.

Komatiites are a type of very rare and ancient type of magmatic rocks, called after the Komati Valley in South Africa, mostly over two billion years old.

Due to their high melting temperatures, magnesium content, and other unique features, komatiites preserve many geochemical clues that help scientists study the evolution of Earth’s mantle.

Komatiites and Earth’s Matter Cycling System

Since they were first discovered in the 1960s, komatiites have attracted geoscientists who study their origins and significance to life on Earth.

Newly-found clues hidden in komatiite rocks suggest Earth’s matter cycling process started way earlier than we previously thought.

An international team of geochemists, led by researchers at the Russian Academy of Sciences, says Earth’s unique process of cycling matter, especially water-bearing elements, may have begun working during its first billion years.

“The mechanism which caused the crust that had been altered by seawater to sink into the mantle functioned over 3.3 billion years ago. This means that a global cycle of matter, which underpins modern plate tectonics, was established within the first billion years of the Earth’s existence, and the excess water in the transition zone of the mantle came from the ancient ocean on the planet’s surface,” said Alexander Sobolev, project leader and co-author of the paper.

Read More: Alien Lifeforms on Mars Could be Hiding in Fettuccine-Like Rocks

Back in 2016, the team conducted a geochemical analysis on 2.7 billion-year-old komatiites found in the Abitibi greenstone belt in Canada. In the mantle’s transition zone, at a depth of 410-660 km, scientists collected data about komatiites’ content in water and other elements like lead, barium, and chlorine.

The results of the analysis led the researchers to form a hypothesis about “an ancient subterranean water reservoir once existed that was comparable in mass to the present-day World Ocean.”

This time, the team investigated the composition of 3.3 billion-year-old komatiite samples collected from the Barberton greenstone belt in South Africa.

In the new paper, published in Nature, the team said:

“Together with an excess of chlorine and depletion of lead in the mantle sources of komatiites, these results indicate that seawater-altered lithosphere recycling into the deep mantle, arguably by subduction, started before 3.3 billion years ago.”

Besides helping us understand how Earth got its fascinating blue color, which it’s losing by the way, through liquid water, komatiites could also be valuable for astrobiology as they could exist on other planets too.

Read More: 4,700-Year-Old Rock Art Immortalizes A Volcano Eruption

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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