Earth’s mantle may reveal origins of life

Scientists have unearthed the deepest column of marine rock ever extracted from Earth’s mantle – the enormous layer below its crust – which could help reveal conditions at the dawn of life.

The rock core was extracted from the Mid-Atlantic Ridge by an international team on the drilling vessel JOIDES Resolution, and is being analysed by The University of Queensland’s Professor Gordon Southam.

“The core was collected during an International Ocean Discovery Project Expedition which managed for the first time to drill 1,268 metres below the seabed into mantle rocks,” Professor Southam said.

“It’s an incredible haul, as previous drilling into this particular type of rock – ocean peridotite – had only reached a maximum depth of 201 metres.

“These samples will help improve our understanding of the links between the Earth’s geology, water chemistry, gases and microbiology.

“Every time the drillers recovered another section of the deep core, we collected samples to culture bacteria.

“We will use these samples to investigate the limits of life in this deep subsurface marine ecosystem, improving our understanding of its origins, and help define the potential for life beyond Earth.”

To understand life’s journey on Earth, the researchers will investigate how olivine, an abundant mineral in mantle rocks, reacts with seawater, leading to a series of chemical reactions that produce hydrogen and other molecules that can fuel life.

The team is now preparing to analyse the core’s nickel content.

“Nickel is required in hydrogenase, the key enzyme allowing these ancient bacteria to use hydrogen in these extreme environments, so we’re currently tracking this through mantle rock,” Professor Southam said.

Unearthed minerals will be examined using electron microscopes at UQ’s Centre for Microscopy and Microanalysis, and ANSTO’s X-Ray Fluorescent Microscope at the Australian Synchrotron, to better understand the effect of seawater circulation on mineral carbonation.

This research is essential for Professor Southam’s work as leader of the UQ Geomicrobiology Group.

“We are researching the role microbiology has in the transformation of carbon dioxide into stable carbonate minerals, and how we can reduce greenhouse gas concentrations in the atmosphere,” he said.

Beyond looking at early life and better ways to sequester carbon, results from the expedition could also have major implications for understanding how magma is formed and leads to volcanism.

“There are amazing discoveries still to be found deep in our Earth, and the data from this expedition is just the start,” Professor Southam said.

“The results will be made public, so we’re hoping that other scientists and enthusiasts can contribute their discoveries about how our world works.”

The research was published in Science.

Image left: A collection of mantle rock samples. Credit: John Lissenberg 

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