A unique study of ancient diamonds has shown that the basic chemical makeup of the earth’s atmosphere that makes it suitable for the explosion of the diversity of life was established at least 2.7 billion years ago. Volatile gases that were preserved in diamonds found in ancient rocks were present in proportions similar to those in today’s mantle, which in turn suggests that the proportions of volatiles in the atmosphere have not changed fundamentally in the last billion years. This shows that one of the basic requirements for sustaining life, the presence of life-giving elements in sufficient quantities, occurred shortly after the earth was formed and has remained fairly constant since then.

During the presentation of the work at the Goldschmidt Geochemistry Conference, lead researcher Dr. Michael Broadly: “The proportion and composition of volatiles in the atmosphere mirrors those found in the Earth’s mantle, and we have no evidence of any significant change since these diamonds were formed 2.7″ billion years ago. ”

Volatile substances like hydrogen, nitrogen, neon, and carbonaceous species are light chemical elements and compounds that can easily be vaporized due to heat or changes in pressure. They are essential to life, especially carbon and nitrogen. Not all planets are volatile; Earth is rich in volatiles, as is Venus, but Mars and the Moon lost most of their volatiles to space. In general, a volatile planet has a better chance of sustaining life, which is why much of the search for life on planets surrounding distant stars (exoplanets) has focused on finding volatiles.

On earth, volatile substances usually gush out of the interior of the planet and are brought to the surface through volcanic eruptions, for example. Knowing when the volatiles arrived in the earth’s atmosphere is the key to understanding when the conditions on earth were suitable for life to originate and develop, but until now there has been no way of knowing those conditions in the deep past understand.

Now French and Canadian researchers have used ancient diamonds as a time capsule to study 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 barely changed in the past 2.7 billion years.

Lead researcher Michael Broadley (University of Lorraine, France) said: “Studying the composition of the modern mantle is relatively straightforward. On average, the mantle begins about 30 km below the surface of the earth, so we can collect samples ejected from volcanoes and examine the liquids and gases trapped in them. However, the constant upheaval of the earth’s crust by plate tectonics means that older samples have been largely destroyed. However, diamonds are comparatively indestructible, they are ideal time capsules. ”

We managed to examine diamonds trapped in 2.7 billion year old, highly preserved rock from Wawa on Lake Superior in Canada. That means the diamonds are at least as old as the rocks they are found in – probably older. It is difficult to date diamonds so we had the lucky opportunity to make sure of the minimum age. These diamonds are incredibly rare and not like the beautiful gemstones we think of when we think of diamonds. We heated it to over 2000 ° C in order to convert it into graphite, which then released tiny amounts of gas for measurement. ”

The team measured the isotopes of helium, neon and argon and found that they were present in proportions similar to those in the upper mantle today. This means that the volatile content is unlikely to have changed much in general, and that the distribution of the major volatile elements between the mantle and the atmosphere has likely remained fairly stable for most of Earth’s life. The earth’s mantle is the part between the earth’s crust and the earth’s core, it comprises around 84% of the earth’s volume.

Dr. Broadley continued, “This was a surprising result. This means that the volatile environment we see around us today is not a new development and thus offers the right conditions for life to develop. Our work shows that these conditions existed at least 2.7 billion years ago, but the diamonds we use can be much older, so it is likely that these conditions were established well before our 2.7 billion year threshold. ”

In a comment, Dr. Suzette Timmerman (University of Alberta, Canada):

“Diamonds are unique samples because they enclose compositions as they are created. The wawa fiber diamonds in particular were a great choice to study – they are more than 2.7 billion years old – and they provide important clues as to their volatile composition during this period, the Neo-Archaic period. It is interesting that the upper mantle appeared to be degassed more than 2.7 billion years ago. This work is an important step towards understanding the mantle (and the atmosphere) in the first half of Earth’s history and paves the way for further questions and research. “

Dr. Timmerman was not involved in this work, this is an independent comment.

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The Goldschmidt Conference is the world’s most important geochemistry conference. It is organized alternately by the European Association of Geochemistry (Europe) and the Geochemical Society (USA). The conference 2021 (virtual) will take place from 4.-9. July instead, https: //2021.goldschmidt.the information/. The 2022 conference will take place in Hawaii.

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