Earth’s formation 4.2 billion years ago led to the development of surface rocks with a layered composition, as hot rocks from the planet’s interior cooled and crystals accumulated over millions of years. The geological evidence of continental crust formation comes from ancient crustal blocks known as krathong. These blocks, called cratons, are billions of years old and form the cores of continents.
The top 10 to 15 kilometers of continental crust contain high concentrations of elements like uranium and thorium, known as radioactive elements. The lower 20 kilometers, however, have very few radioactive elements. The cause of this differentiation is still a topic of debate among geoscientists.
A study by researchers Andrew J. Smyi and Peter B. Keleman explored the possibility of ultrahigh temperature metamorphism causing crustal differentiation of radioactive elements. They analyzed rocks subjected to various pressures and temperatures, creating mathematical models to compare the changes in concentrations of radioactive elements under different conditions.
The researchers found that temperatures above 900 degrees Celsius are necessary to dissolve minerals like zircon and monazite in the lower crust, leading to enrichment of uranium and thorium in the upper continental crust. These temperatures are associated with plate movement and collision, suggesting that the evidence of Earth’s differentiation has been preserved for over 3 billion years.
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Source: sciworthy.com
