How was the Earth formed?
The Earth was formed about 4.567 billion years ago by accretion from protoplanetary
Most of the Earth was molten due toactive volcanism and frequent collisions with other space objects. One such major collision is believed to have tilted the Earth's axis and formed the Moon.
Over time, such space bombingstopped, which allowed the planet to cool down and form a solid crust. The water delivered to the planet by comets and asteroids condensed into clouds and oceans. The earth finally became hospitable to life, and its earliest forms enriched the atmosphere with oxygen.
Protoplanetary disk as seen by the artist
Formation of the first continents
Geophysicists discovered that about 3 billion years agothe earth's crust swelled in a spike in growth. According to scientists, just 1.5 billion years after the formation of the Earth, the mantle - a layer of silicate rock between the crust and the outer core, has become very hot. Magma seeped into fragments of older crust above it. These fragments are the beginnings of the growth of modern continents.
Evidence of planetary growth was found inancient zircon crystals in sediments at the bottom of streams in Greenland. The extremely hard crystals, composed of zirconium silicate, formed during a growth spurt about 3 billion years ago.
There were probably several events in the history of the Earth during which the crust was formed. But this global injection, which occurred 3 million years ago, was definitely one of the largest.
Chris Kirkland, Professor of Geosciences at Curtin University
Prior to this leap, the Earth's ancient crust was much thinner and weaker than it is today. In the end, it disintegrated into fragments of the bark, from which a new one could grow.
At that time, the temperature of the mantle peaked due toradioactive decay of elements such as uranium and potassium in the Earth's core. It also raised temperatures and residual heat after the planet formed. Global temperatures spurred growth, and the crust continued to swell for about 200 million years, the researchers said.
What were the first continents like?
Geologists at Monash University shed new light on the early history of the Earth: they stated that the continents were weak and prone to collapse in the early period.
We reproduced the conditions of the early Earth incomputer numerical models and showed that the release of internal primary heat, three to four times the present, caused a large melting in the shallow mantle, which was then forced out in the form of magma (molten rock) to the Earth's surface.
Fabio Capitanio, doctor and lead author of the study
According to the researchers, the small mantle left over from this process was dehydrated and solidified and formed the foundations of the first continents.
The results of the work explain that the continents previouslywere weak and prone to destruction: about 4.5 or 4.0 billion years ago. They then gradually differentiated and became rigid over the next billion years, and later formed the core of our modern continents.
The quantitative model used in the study explains the levels of mantle melting and layered structures found in most cratons on Earth.
This explains the transition from Hadei, whichcovers the first 500 million years of earth's history, during which the crust was completely reworked, to Archean (four to three billion years ago), when the continents just solidified.
The collision of the Earth with the planet Theia as seen by the artist.
What disappeared during the formation of the Earth?
Scientists have created a model of the radioactivity of the ancientsrocks of the Earth: it questions modern models of the formation of the continental crust. It is assumed that the continents rose from the sea much earlier than previously thought, but were destroyed and no trace remains of them.
Scientists from the University of Adelaide have published twostudies of the model of radioactivity of rocks for billions of years. They showed that the Earth's continental crust may have been thicker, much earlier than current models suggest, and the continents may have existed as far back as four billion years ago.
If our model is correct, it canrequire a revision of many aspects of our understanding of the chemical and physical evolution of the Earth, including the rate of continental growth and possibly even the beginning of plate tectonics.
Dr. Hasterock and his graduate student Matthew Gard collected75,800 geochemical samples of igneous rocks (such as granite) believed to have formed with the first continents. They estimated the radioactivity in these rocks today and built a model of the average radioactivity from four billion years ago to the present.
All breeds, scientists explain, containnatural radioactivity that produces heat and raises the temperature in the crust. It breaks down and the more radioactive the rock, the more heat it produces.
Rocks commonly associated with continental crusthave a higher radioactivity than oceanic rocks. A rock that is four billion years old would have about four times the radioactivity it is today.
But researchers have found an unexpected shortagethe level of radioactivity in rocks older than about two billion years. When they adjusted for higher heat production due to the higher radioactivity that should have been present, the deficit disappeared.
Scientists think that this was due to high radioactivity and high temperatures: the rocks either melted or were easily destroyed by tectonic movement.
Modern models say the continentsemerged from the oceans as the earth's crust thickened. The authors believe that a significant amount, albeit very unstable, continental crust could have existed much earlier.
The connection between life on Earth and the movement of continents
A new study by the University of Texas atAustin shows a possible connection between life on Earth and the movement of continents. These results confirm that sediments, which are often made up of pieces of dead organisms, may play a key role in determining the speed of continental drift.
The study describes how deposits,moving under tectonic plates, or subducting beneath them, can regulate plate movement and even influence the rapid rise of mountain ranges and the growth of continental crust.
Sediment forms when wind, water and ice erode existing rocks or when shells and skeletons of microscopic organisms such as plankton accumulate on the seabed.
It has long been known that sediments falling into zonessubduction, affect geological activity, for example, the frequency of earthquakes. But until now, it was believed that they have little effect on the movement of the continents. This is because the subduction rate was thought to depend on the strength of the subduction plate.
Continental movement is driven by immersionone plate under the other, so here the strength of the part of the plate, which plunges into the Earth's mantle (and the energy required for its bending), determines the speed of its movement, but the sediment has little effect.
However, early research involving scientistsUTIG showed that subduction plates can be weaker and more sensitive to other influences than previously thought. This led researchers to look for other mechanisms that could affect the speed of the plates.
They appreciated how different types of rockscan affect the slab interface - the boundary where subductive slabs meet. Subsequent simulations have shown that sediment rock can create a lubricating effect between the plates, thus accelerating subduction and increasing plate speed.
This mechanism can set in motion a complexfeedback loop. As the plate speed increases, there will be less time for sediment accumulation, so the amount of subductive sediment will decrease.
This leads to slower subduction, whichmay allow mountains to grow at plate boundaries, as the force of two plates colliding with each other causes a rise. In turn, the erosion of these mountains by wind, water and other forces can lead to the formation of more sediment, which returns back to the subduction zone and resumes the cycle, increasing the rate of subduction.
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