New Theory About the State of Earth Billions of Years Ago: Clearer Insight Into Earth’s Hidden Crystals

A transmitted light view through a 200-micron section of a peridotite sample, showing the three main minerals — olivine (clear-green), orthopyroxene (grey-green) and garnet (pink).
Credit: Dr. Emma Tomlinson, Trinity College Dublin.

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

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

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

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

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

“Many rocks from the mantle below old continents contain a surprising amount of silica — much more than is found in younger parts of the mantle.”

“There is currently no scientific consensus about the reason for this.”

The new research, which looks at the global data for mantle peridotite, comes up with 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– greater than 1700 °C — interacted with older parts of the mantle and this caused the growth of silica-rich minerals.

“For more than 1 billion years, from 3.8 to 2.5 billion years ago, volcanoes also erupted very unusual lavas of very low viscosity — lava that was very thin, very hot and often contained variable levels of silica,” Dr. Tomlinson added.

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