Through new studies focused on komatiitic magma, geochemists associated with the Russian Academy of Sciences (RAS) now believe that our world's unique way of cycling matter, and particularly the elements that comprise water, indicate that the Earth's absorption of oceanic matter into its mantle may have begun as early as the first billion years our planet existed.
Earth cycles matter through a highly extraordinary process known as convection. During this mechanism, hot magma rises in the Earth's mantle and pushes other water-bearing minerals ever-deeper down into the mantle. A transition zone is reached wherein the pressure of this tectonic movement squeezes the water out of the minerals, like the wringing of a wet towel.
Established notions of the origin and architecture of the subterranean ocean resident in Earth's mantle were founded largely on work done in 2016 by a troupe of international scientists from the Vernadsky Institute for Geochemistry and Analytical Chemistry. Studying in the Canadian Abitibi greenstone belt, a strip of komatiitic magma that is 2.7 billion years old, data regarding mutable features like lead and barium was extracted from the mantle's transition zone at depths ranging between 410-660km.
From this first set of data, the hypothesis sprang that a mammoth, subterrestrial cistern of water equivalent in size to the World Ocean existed. Learn more about the initial discovery of the underground ocean below.
What exactly is a komatiite?
Billions of years ago, the Earth's crust was structured on a kind of volcanic rock that has altered in composition so vastly in the intervening ages as to no longer bear fruit for scientists who wish to know more about the "volatile" (or mutable) components, such as water, within them. These ancient volcanic rocks are called komatiites.
Komatiites are useful to geochemists, however, because they do retain fragments of olivine, a magmatic mineral that maintains micron-sized inclusions of solidified magma that were protected from obscuring changes during crystallization. These inclusions can tell scientists vital details about hydrogen in the isotopic state, as well as the chlorine and water contents of komatiitic melts.
So what's new?
A recent study spearheaded by Alexander Sobolev, a member of the Russian Academy of Sciences and Doctor of Geological and Mineralogical Sciences, worked with a more high-intensity magma-heating apparatus applied to samples taken from the Barberton greenstone belt in South Africa.
The Barberton belt is believed to be 3.3 billion years old, thus significantly younger than the Abitibi belt, yet relinquishing geochemical information that suggests the aforementioned subterranean reservoir in the Earth's mantle predates the Palaeoarchaean era. This means the water was present 600 million years earlier than has been heretofore believed.