Scientists have detected primordial chemical signatures preserved within modern kimberlites, according to new research by a multi-national team involving a University of Alberta scientist. The results provide critical insight for understanding the formation of Earth.
"Knowing the chemical signature of Earth's original building blocks is the holy grail of geochemistry," said Graham Pearson, author on the study. "This knowledge can help us understand the formation of the planets in the solar system as well as their relationship to each other."
The research team analyzed kimberlites--a type of rock formed by cooling magma that sometimes carries diamonds--from around the world, including many from Canada.
"We found that kimberlites' chemical signatures are remarkably uniform and very like the chondritic building blocks thought to have formed the Earth 4.55 billion years ago," added Pearson, professor in the Department of Earth and Atmospheric Sciences, Henry Marshall Tory Chair, and Canada Excellence Research Chair Laureate. "We think this is the cleanest signal of this primordial signature found in any group of rocks on Earth."
The interior of our planet is constantly cycling, as minerals at Earth's surface are continually returned to great depths through movement of the tectonic plates. "This mixing makes it very difficult to detect the starting ingredients--a bit like trying to detect the brand of flour that was used by tasting an over-cooked cake," explained Pearson. "The final twist is that in the last 200 million years, these signatures became more scarce, likely due to events associated with the breakup of the supercontinent, Pangaea."
The discovery of these ancient, primordial signatures suggest that reflect the melting of deep, isolated regions of pristine material within the Earth that have remained untouched by billions of years of tectonic plate recycling--revealing a glimpse of the holy grail that will shed new light on how Earth, and planets like it, formed.
The paper, "Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir," was published in Nature (doi: 10.1038/s41586-019-1574-8).