Ancient life existed in Earth’s mantle rocks, fossilised microbes indicate

By: | Updated: September 3, 2015 10:44 AM

Ancient rocks harboured microbial life deep below the seafloor in Earth's mantle, scientists have found, reinforcing that life springs up anywhere there is water, even in seemingly hostile environments.

Ancient rocks harboured microbial life deep below the seafloor in Earth’s mantle, scientists have found, reinforcing the theory  that life springs up anywhere there is water, even in seemingly in very hostile environments.

This new evidence was contained in drilled rock samples of Earth’s mantle – thrust by tectonic forces to the seafloor during the Early Cretaceous period.

The discovery confirms a long-standing hypothesis that interactions between mantle rocks and seawater can create potential for life even in rocks deep below the ocean floor, researchers said.

The fossilised microbes are likely the same as those found at the active Lost City hydrothermal field in the Mid-Atlantic Ridge, they said.

This is significant because researchers believe the Lost City is a present-day analogue to ancient hydrothermal systems on early Earth where life may have emerged.

“During our analysis of the rock samples, we discovered organic-rich inclusions that contained lipids, proteins and amino acids – the building blocks of life – mummified in the surrounding minerals,” said lead author Frieder Klein, an associate scientist at Woods Hole Oceanographic Institution (WHOI), Virginia Tech in US.

This study focused on mantle rocks that were originally exposed to seawater approximately 125 million years ago when a large rift split the massive supercontinent known as Pangaea.

The rift, which eventually evolved into the Atlantic Ocean, pulled mantle rocks from Earth’s interior to the seafloor, where they underwent chemical reactions with seawater, transforming the seawater into a hydrothermal fluid.

“The hydrothermal fluid likely had a high pH and was depleted in carbon and electron acceptors,” Klein said.

“However, the hydrothermal fluid contained hydrogen and methane and seawater contains dissolved carbon and electron acceptors,” Klein said.

“So when you mix the two in just the right proportions, you can have the ingredients to support life,” Klein said.

“This research makes the connection all the way from convection of the mantle to the break-up of the continents to ultimately providing geochemical options for microbiology,” said Everett Shock, a professor at Arizona State University’s School of Earth and Science Exploration in US.

The rock samples analysed in the study were originally drilled from the Iberian continental margin off the coast of Spain and Portugal in 1993.

During the expedition aboard the research vessel, researchers drilled through 690 metres of mud and sediment deposited onto to the ocean floor to reach the ancient seafloor created during the break-up of the supercontinent Pangaea and the opening of the Atlantic Ocean.

The study reinforces the idea that life springs up anywhere there is water, even in seemingly hostile geological environments – a tantalising prospect as scientists find more and more water elsewhere in the solar system.

The study was published in the journal PNAS.

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