A unique study of ancient diamonds has shown that the basic chemical composition of the Earth’s atmosphere, which makes it conducive to the explosion of the diversity of life, was established at least 2.7 billion years ago . The volatile gases retained in the diamonds found in ancient rocks were present in proportions similar to those found in the present mantle, which in turn indicates that there has been no fundamental change in the proportions of volatiles in the atmosphere over the past billions of years. This shows that one of the basic conditions for sustaining life, the presence of life-giving elements in sufficient quantity, arose soon after the formation of the Earth and has remained fairly constant ever since.
Presenting the work at the Goldschmidt Geochemistry Conference, Principal Investigator Dr Michael Broadly said: “The proportion and composition of volatiles in the atmosphere mirror those found in the mantle, and we have no evidence a significant change since these diamonds were formed 2.7 billion years ago ”.
Volatile substances, such as hydrogen, nitrogen, neon and carbonaceous species, are light chemical elements and compounds, which can be easily vaporized due to heat or pressure changes. They are necessary for life, especially carbon and nitrogen. Not all planets are rich in birds; The Earth is rich in birds, as is Venus, but Mars and the Moon have lost most of their birds in space. In general, a planet rich in volatiles has a better chance of sustaining life, which is why much of the research for life on planets surrounding distant stars (exoplanets) has focused on finding volatiles.
On Earth, volatile substances mainly bubble from the interior of the planet and are brought to the surface by volcanic eruptions. Knowing when the birds first arrived in Earth’s atmosphere is essential to understanding when conditions on Earth were right for the origin and development of life, but until now there was no way to understand these conditions. in the distant past.
Today, French and Canadian researchers have used ancient diamonds as a time capsule to examine 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 2.7 billion years.
Principal Investigator Michael Broadley (University of Lorraine, France) said: “Studying the composition of the Earth’s modern mantle is relatively straightforward. On average, the mantle layer begins about 30 km below the Earth’s surface, so we can collect samples released from volcanoes and study the fluids and gases trapped within. However, the constant churning of the earth’s crust via plate tectonics means that the older samples have mostly been destroyed. However, diamonds are relatively indestructible, they are ideal time capsules ”.
We have successfully studied the diamonds trapped in the highly preserved 2.7 billion-year-old Wawa rock on Lake Superior in Canada. This means that diamonds are at least as old as the rocks they are in – probably older. Diamonds are difficult to date, so it gave us a lucky chance to be sure of the minimum age. These diamonds are incredibly rare and do not look like the beautiful gemstones we think of when we think of diamonds. We heated them to over 2000 C to transform them into graphite, which then released tiny amounts of gas for the measurement ”.
The team measured the isotopes of helium, neon and argon and found that they were present in proportions similar to those found in the upper mantle today. This means that there was probably little change in the proportion of volatiles in general, and that the distribution of essential volatiles between mantle and atmosphere is likely to have remained fairly stable for most of the period. life on Earth. The mantle is the part between the earth’s crust and the core, it represents about 84% of the volume of the Earth.
Dr Broadley continued: “It was a surprising result. This means that the volatile environment that we see around us today is not a recent development, thus providing the right conditions for life to thrive. 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 is likely that these conditions were established well before our threshold of 2, 7 billion years ”.
Commenting, Dr Suzette Timmerman (University of Alberta, Canada) said:
“Diamonds are unique samples because they block compositions during their formation. Wawa’s fibrous diamonds in particular were an excellent selection to study – they’re over 2.7 billion years old – and they provide important clues to the volatile makeup of this period, the Neoarchean period. Interestingly, the upper mantle appears to be degassed over 2.7 billion years ago. This work is an important step towards understanding the mantle (and 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.