Ancient diamonds show Earth was primed for life at least 2.7 billion years ago

·3-min read
An ancient diamond
An ancient diamond

Ancient diamonds indicate that Earth was primed for life’s explosion at least 2.7 billion years ago, researchers have said.

Volatile gases conserved in diamonds found in ancient rocks were present in similar proportions to those found in the Earth’s mantle – which lies between the planet’s core and crust.

This indicates there has been no fundamental change in the proportions of these gases in the atmosphere over the last few billion years.

The research suggests that one of the basic conditions necessary to support life, the presence of life-giving elements in sufficient quantity, appeared soon after Earth formed, and has remained fairly constant ever since.

Presenting the work at the Goldschmidt Geochemistry conference, lead researcher Dr Michael Broadley, said: “The proportion and make-up of volatiles in the atmosphere reflects that found in the mantle, and we have no evidence of a significant change since these diamonds were formed 2.7 billion years ago.”

Volatiles such as hydrogen, nitrogen, neon, and carbon-bearing species are light chemical elements and compounds, which can be readily vaporised due to heat, or pressure changes.

They are necessary for life, especially carbon and nitrogen.

On Earth, volatile substances mostly bubble up from the inside of the planet, and are brought to the surface through events such as volcanic eruptions.

Knowing they arrived in the Earth’s atmosphere is key to understanding when the conditions on the planet were suitable for the origin and development of life, but until now there has been no way of understanding these conditions in the deep past.

Now French and Canadian researchers have used ancient diamonds as a time capsule, to examine the conditions deep inside the Earth’s mantle in the distant past.

Studies of the gases trapped in these diamonds show that the volatile composition of the mantle has changed little over the last 2.7 billion years.

Dr Broadley, of the University of Lorraine, France said: “Studying the composition of the Earth’s modern mantle is relatively simple.

“On average, the mantle layer begins around 30km below the Earth’s surface, and so we can collect samples thrown up by volcanoes and study the fluids and gases trapped inside.

“However, the constant churning of the Earth’s crust via plate tectonics means that older samples have mostly been destroyed.

“Diamonds however, are comparatively indestructible, they’re ideal time capsules”.

Researchers studied diamonds trapped in 2.7 billion-year-old highly preserved rock from Wawa, on Lake Superior in Canada.

This meant they were at least as old as the rocks they were found in – probably older.

It can be difficult to date diamonds, so this gave researchers the chance to be sure of the minimum age.

These stones were incredibly rare, and not like the beautiful gems that come to mind when people think of diamonds.

They were heated to more than 2000C to transform them into graphite, which then released tiny quantities of gas which was measured.

The team measured the isotopes of Helium, Neon, and Argon, and found they were present in similar proportions to those found in the upper mantle today.

This suggests there has probably been little change in the proportion of volatiles generally, and that the distribution of essential volatile elements between the mantle and the atmosphere are likely to have remained fairly stable throughout the majority of Earth’s life.

Dr Broadley added: “This was a surprising result. It means the volatile-rich environment we see around us today is not a recent development, so providing the right conditions for life to develop.

“Our work shows that these conditions were present at least 2.7 billion years ago, but the diamonds we use may be much older, so it’s likely that these conditions were set well before our 2.7 billion year threshold.”

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