What exactly scientists have found out
The state of the planet and the processes that occurred on it 3 billion years ago,
However, there are several regions where ancientrocks come close to the surface. One of them is Panorama, an arid and sparsely populated region in Western Australia, where scientists from the University of Colorado have recovered core samples dating back about 3.24 billion years.
In this area, a slab comes to the surface,which in the Archean was at the bottom of the ocean. Scientists have used this to determine the content of various types of oxygen in its rocks, which accumulate in minerals when they interact with sea water. Specifically, they analyzed the relative amounts of two isotopes, light oxygen-16 and slightly heavier oxygen-18, in over 100 samples.
Analysis showed that the number of these isotopessignificantly exceeds their content in rocks that are washed by sea water right now. Scientists believe that this result suggests that about 3.24 billion years ago, there was practically no land on Earth, and the entire surface was covered with water.
"Without continents over the ocean, oxygen values would be different than they are today, and that's exactly what we found," wrote study lead author Benjamin Johnson.
However, the results of the study do not mean thatThe Earth was completely devoid of land - researchers believe that during this period of the planet’s development, “microcontinents” could exist on its surface, which rose above the surface of the ocean at a great distance from each other.
Moreover, the analysis with a high degree of probabilityexcludes the existence of huge soil-rich continents such as those that dominate Earth today, as well as supercontinents such as the hypothetical Vaalbara.
Vaalbara- the first hypothetical supercontinent on Earth,which presumably existed during the Archean era - 3.6–2.8 billion years ago. Its formation, according to scientists’ hypothesis, began 3.6 billion years ago and ended 3.1 billion years ago. The supercontinent broke into smaller ones about 2.5 billion years ago.
“I present a picture similar to howthe Galapagos Islands look when viewed from the west: huge expanses of the ocean to the north and south with small rocky volcanic islands barely rising above the ocean surface, ”Johnson comments.
Parts of the ancient supercontinent Vaalbar in the territories of modern continents - Africa and Australia
However, other explanations for the very highthe content of oxygen isotopes in rocks of that period, the study authors note. The same chemical characteristics could arise if the continents formed much more slowly than scientists believe.
Another hypothesis is that continental clays, which are now solid rocks, did not form on land, but in the ocean.
What was on Earth besides the ocean
Hypotheses about exactly how and when on EarthThe first continents formed are still a matter of debate among scientists. There is a theory that large areas of land on the surface of the planet appeared as a result of slowing down the loss of heat from the bowels of the Earth.
The oldest surviving continentalmaterials are about 4 billion years old - that is, it was formed about 600 million years after the formation of the planet. If so, it originated even before the Earth began to be bombarded by debris from the formation of the solar system - and before water appeared on the planet. However, scientists have not yet been able to find strong evidence of the existence of continents before Gondwana.
Gondwana
Photo: By Fama Clamosa — Own work, CC BY-SA 4.0.
Gondwana
Most researchers agree thatAbout half a billion years ago, the Earth was dominated by the supercontinent Gondwana, which existed before the Jurassic period and broke apart about 180 million years ago.
Gondwana included Africa, South America,Antarctica, Australia, New Zealand, as well as Arabia, Madagascar and Hindustan. It was formed at the end of the Precambrian as a result of the split of the supercontinent Rodinia.
Approximately 3 billion years ago, during the period describedAccording to the authors' research, the geological era of the Archean (2.5–4 billion years ago) was ending on Earth. It is believed that at this time there was practically no free oxygen in the planet’s atmosphere, and the amount of greenhouse gases was many times higher than current levels.
Life on Earth appeared at the beginning of the Archean, and by 3 billion years ago the dominant form of life on Earth were cyanobacterial mats (stromatolites) and archaea.
Stromatolites outwardly resembled stones, but inwere actually conglomerates of living bacteria. They included aerobic and anaerobic bacteria, which, through photosynthesis, converted sunlight and water into glucose, a simple form of sugar. During this process, oxygen was released as a by-product.
Stromatolites
Scientists believe that modern plate tectonics withits subduction zones, distribution centers, earthquakes and all other features known to us, probably also began in the Archean era - about 3.2 billion years ago.
This is proven by rock samples from the ancient earth's crust.aged from 3.9 billion to 2.5 billion years old, found by scientists in South-West Greenland. The researchers analyzed the number of neutrons in the hafnium atoms to find out how long each sample had been part of the Earth's crust.
As the rocks surfacemelted and processed, the content of hafnium isotopes in them changes. The scientists found that the concentration of hafnium in older rocks, which are more than 3.2 billion years old, is significantly different from the amount in younger ones. Scientists explain this difference by the fact that plate tectonics began on Earth around this time.
According to one theory, at the beginning of the Archean era, vertical jets of very hot magma in the mantle likely delivered material directly to the Earth's surface, forming the first chunks of continental crust.
Gradually - between 3.2 and 3.5 billion years ago -the mantle cooled down and there were fewer hot magma plumes. The researchers believe that stable convection cells formed in the mantle, which began to control plate movements and subduction, and plate tectonics began to shape the Earth's surface.
Since then, most of the new crust has penetratedthe surface of the Earth in those places where the distribution centers are located, and in the subduction zones. One example is the Mariana Subduction Zone, where the Mariana Island Arc formed and the Mariana Trench is the deepest place in the ocean.
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