The First Continents On Earth Appeared Earlier Than Geologists Thought
American scientists have found on the territory of Australia deposits of the oldest rocks of the Earth, which preserved traces of the movement of the first continents on the planet. This suggests that tectonic processes on Earth began very early. The research was published in the scientific journal Science Advances.
"This is just one of the evidence that the history of the movement of tectonic plates begins with the very first epochs of the planet's existence. The rocks we found increase the probability that this was indeed the case, and suggest that the early Earth was much more similar to itself today than is commonly believed," commented one of its authors, a geologist from Harvard University Alec Brenner.
The earth's interior consists of several layers – a solid crust, a semi-liquid mantle, and molten metal core. The crust is divided into several huge fragments – tectonic plates that slowly "float" on the surface of the mantle and collide with each other. As a result of these collisions, continents, mountain ranges, and other major terrain irregularities appear and disappear.
In recent years, scientists have begun to actively discuss when these plates began to move and when the first continents appeared on Earth. In recent years, geologists have found a lot of theoretical and practical evidence in favor of the fact that this could have happened almost immediately after the formation of the planet, and about 3.2 billion years ago.
Riddles of ancient Earth
New evidence that tectonic processes on our planet appeared very early, Brenner and his colleagues found during excavations in Western Australia. They studied the deposits of the so-called Greenstone belts in the Pilbara region. These deposits were formed approximately 3.2-3.6 billion years ago. Scientists consider them the oldest preserved examples of the earth's primary crust, along with similar deposits in Greenland and South Africa.
Geologists have long studied such rocks in the hope of finding traces of the earliest earth life, as well as ancient tectonic processes and magnetic fields, without which, according to scientists, the Earth could not exist. The first task was completed a year ago by Australian geologists, who found traces of colonies of ancient microbes in sediments that are 3.48 billion years old.
These rocks, as noted by American geologists, often contain minerals and crystals that were formed at high temperatures and preserved a kind of "imprint" of the earth's ancient magnetic field. As a rule, scientists usually use such structures to estimate the strength of the planet's magnetic "shield," but Brenner and his colleagues found a different use for them.
Their idea was based on a simple assumption: if plate tectonics and continents already existed, then their movement would have a special effect on how traces of the planet's magnetic field were "imprinted" in their rocks. Accordingly, by comparing different samples of ancient crust extracted from different regions of the Greenstone belt, it is possible to calculate quite accurately the speed of their parent continent at that time.
Based on similar considerations, geologists measured the magnetization of two hundred samples of ancient rocks that were mined in two dozen different points of the Pilbara platform, and also obtained similar data for minerals from South Africa. Their subsequent comparison showed that tectonic plates existed as early as 3.2 billion years ago. At the same time, the speed of their movement-about 2.5 centimeters per year-is comparable to the speed of modern continents and plates.
According to researchers, this indicates that tectonic processes appeared on Earth unexpectedly early and quickly acquired the properties that are characteristic of them now. The discovery of other deposits of The earth's oldest rocks, as Brenner and his colleagues' hope, will help them understand where and when the "cycle of continents" was started.