Geologists developed a new theory of the state of the Earth billions of years ago after examining very old rocks formed in the Earth’s mantle below the continents.
Assistant Professor Emma Tomlinson of Trinity College Dublin and Queensland University of Technology professor Balz Kamber have just published their research in a leading international journal, Nature Communications.
Seven continents on Earth today are built around a stable interior called the craton, and geologists believe that the stabilization of the craton some 2.5 – 3 billion years ago was crucial for the emergence of terrestrial masses on Earth.
Little is known about how the cratons and supporting keels of the mantle formed, but important traces can be found in the xenoliths of peridotites, which are mantle specimens that are brought to the Earth’s surface by volcanic eruptions.
Dr Tomlinson of Trinity’s School of Natural Sciences said:
“Many of the mantle rocks below the old continents contain a surprising amount of silicon dioxide – much more than is found in the younger parts of the mantle.”
“There is currently no scientific consensus on the reason for this.”
New research, which deals with global data for peridotitis in the mantle, provides a new explanation for this observation.
The research used a new thermodynamic model to calculate that unusual mineralogy developed when very hot molten rock – greater than 1700 ° C – interacted with older parts of the mantle, causing the growth of minerals rich in silica.
“For more than a billion years, from 3.8 to 2.5 billion years ago, volcanoes also erupted very unusual lava of very low viscosity – lava that was very thin, very hot and often contained variable levels of silicon dioxide,” he added. is Dr. Tomlinson.
“Our modeling suggests that the unusual lavas are actually molten rocks that interact with the mantle at great depths and that interaction has resulted in variable levels of silicon dioxide.”
Professor Kamber, QUT, said:
“Both silicon rocks in the deep mantle and low-viscosity volcanic rocks stopped the Earth from forming about 2.5 billion years ago. This time is the boundary between the Archean and Proterozoic eons – one of the most significant disruptions in the Earth’s eons is the geological time frame.”
What caused this boundary remains unknown, but research offers a new perspective.
Professor Kamber added:
“This may have been due to a change in the way the mantle flowed. Once the mantle began to rotate slowly all the way to the core (2,900 km), very high temperatures of the Archean eon were no longer possible.”
Source of the story:
Material provided Trinity College Dublin. Note: Content can be edited for style and length.