The continental crust of our planet could begin to form a billion years earlier than it is believed.
Our planet is notable for its long and uninterrupted geological activity, and its most ancient rocks have long been “recycled” by these processes. It is believed that the continents themselves, with their continental plates as a whole, were formed only about 2.5-3 billion years ago, when the Earth was already 3.5-4 billion years old. The corresponding rocks appear in the “geological record” at that time.
However, Australian geologists believe that the continental crust is much older and formed 4-4.5 billion years ago. Derrick Hasterok and his colleagues from the University of Adelaide report this in articles (1, 2) published in the journals of Precambrian Research and Lithos.
The authors analyzed a total of 75,800 samples of igneous rocks collected on different continents, determining the content of radioactive isotopes. Disintegrating over time, they can serve as natural chronometers, allowing you to determine the age of a rock. So, scientists have noticed an unexpected drop in radioactivity in samples older than two billion years.
To explain this anomaly, they suggested that the continental plates at that time were already more massive than is commonly believed. Reheating more strongly under the influence of internal friction and radiation, they were more “processed” by tectonic processes.
As a result, the most ancient rocks have not survived to our time or have been preserved in extremely insignificant quantities, having shifted the dating of the appearance of the continents for a shorter period. “The dominant model suggests that continents form after oceanic plates, as the crust thickens,” says Derrick Hasterok. “But we think that significant amounts of continental crust, although very unstable, existed before.”