A New Clearer Glimpse of Earth’s Hidden Crystals

Geologists developed a new theory about the state of the Earth billions of years ago after examining the very old rocks that formed in the Earth’s mantle under the continents.

Assistant Professor Emma Tomlinson of Trinity College Dublin and Professor Balz Kamber of Queensland University of Technology have just published their research in a leading international journal, Nature communications.

The seven continents on Earth today are each built around a stable interior called a craton, and geologists estimate that the stabilization of the craton 2.5 to 3 billion years ago was essential for the emergence of land masses. on earth.

Little is known about the formation of cratons and their supporting mantle keels, but important clues can be found in peridotite xenoliths, which are mantle samples that are brought to the Earth’s surface by volcanoes. erupting.

Dr Tomlinson, from Trinity’s School of Natural Sciences, said:

“Many mantle rocks under old continents contain a surprising amount of silica – much more than what is found in younger parts of the mantle.”

“There is currently no scientific consensus as to why this is.”

The new research, which examines global data on mantle peridotite, offers a new explanation for this observation.

The research used a new thermodynamic model to calculate that the unusual mineralogy developed when very hot molten rock – above 1,700 ° C – interacted with older parts of the mantle, causing the growth of silica-rich minerals.

“For over a billion years, 3.8 to 2.5 billion years, volcanoes also erupted very unusual lava of very low viscosity – lava that was very thin, very hot and often contained varying levels of silica, ”added Dr Tomlinson.

“Our modeling suggests that the unusual lavas were in fact the molten rocks that interacted with the mantle at great depth and this interaction resulted in a varying level of silica.”

Professor Kamber, QUT, said:

“Deep mantle silica-rich rocks and low-viscosity volcanic rocks ceased to be produced by the Earth about 2.5 billion years ago. This moment is the border between the Archean and Proterozoic eons – one of the most important ruptures in earth’s geology. time scale. “

The cause of this border remains unknown, but research offers a new perspective.

Professor Kamber added:

“This may be due to a change in the way the mantle flowed. Once the mantle began to slowly turn over to the core (2,900 km), the very high temperatures of the Archean Aeon were no longer. possible. ”