"Formed very quickly": Russian scientist on the appearance of water on Earth and the geological history of our planet

- Anatoly Mikhailovich, recently American geologists refuted one of the theories of water formation on Earth. They believe that meteorites that fell to Earth at the beginning of its formation were not the main source of water on the planet, since they had an extremely low content of it. What do you think about that? How did water appear on Earth?

- Traditionally, it is believed that water on Earth appeared as a result of the fall of comets composed of water. How the water ended up in these comets is unknown, scientists are investigating this question. In particular, it was discovered that comet Hartley-2, which often flies over the Earth, contains water, the isotopic composition is very similar to the Earth's.

At first, water was on Earth in a state of vapor, in the atmosphere. But about 4.4 billion years ago, when the planet's surface temperature dropped below the boiling point of water, water from the atmosphere fell to Earth. Meteorites also brought silicate and metallic substances to Earth, from which the earth's mantle was eventually formed.

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The Earth has a layered structure, it consists of solid silicate shells (crust and mantle) and a metal core. Today, silicates are the most abundant minerals on Earth. These include, for example, important non-metallic minerals: asbestos, talc, mica, kaolin, ceramic and refractory raw materials.

-- There are two main hypotheses about the origin of the Earth. One suggests that the Earth grew relatively quickly (from 2 to 5 million years), capturing the water and gases necessary for life from the cloud surrounding the young Sun. The other talks about dust particles that turned under the irradiation of the Sun into celestial bodies - planetesimals, which became the source of the necessary compounds. Which of the theories is closest to the truth?

- These hypotheses are being discussed. It is known that there was a giant interstellar cloud of cosmic matter and as a result of some kind of collapse, the solar system and planets were formed. This happened about 4.6 billion years ago.

However, it is not known at what speed the Earth was formed then. If it formed quickly, then initially it was molten, if slowly, then it was a solid celestial body. Now most scientists are inclined to believe that the Earth was formed very quickly, this led to its stratification into a core and an iron-silicate mantle.

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- The Earth was formed about 4.5 billion years ago. How did scientists determine this particular age of the planet? What geological finds and studies made it possible to establish it?

Researchers have found that the age of the most ancient rocks on Earth is about 4 billion years. For example, there is such a mineral - zircon, the study of which is given great attention. Thanks to him, scientists can get a lot of information about how the continents evolved and the mineral resources of the Earth were formed. It is believed that zircon was formed when lithospheric plates collided as a result of tectonic movements. Due to its high resistance to erosion, the mineral has remained unchanged, there are even samples up to 4.4 billion years old.

The age of the Earth at 4.5 billion years was established on the basis of the study and dating of the oldest meteorite samples found on Earth, formed before the beginning of the formation of planets.

— How did the formation of the Earth differ from the point of view of geology at different stages of the planet's development from other planets in the solar system? What are the differences and similarities?

- All the terrestrial planets - Mercury, Venus, Earth and Mars - were formed approximately simultaneously and according to a similar scenario. In their formation, the main role was played by silicates from meteorites. In the formation of the distant planets or giant planets of Jupiter and Saturn, hydrogen and helium participated. However, inside Jupiter there is also a metallic core, a silicate-iron "mini-Earth", and on top of the planet is surrounded by a gas shell.

If we return to the terrestrial planets, then only on Earth there are continents, oceans and different types of crust are represented - continental and oceanic. Venus, for example, is the same in size, but it has a completely different geological history, it is dominated by volcanism. Eruptions played a key role in shaping the planet's surface. Most of Venus is made up of basaltic rocks.

• Internal structure of Jupiter
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- When studying the geological history of the Earth, it is customary to use such concepts as geological eras, periods. For example, it is known that in the Paleozoic era there was active volcanic activity, at this time many modern mountain ranges were formed - the Ural Mountains, the Tien Shan, the Appalachians. What are the most significant periods that made the Earth what it is now, and created the conditions for the emergence of life?

- The geological history of the Earth has been documented since 4 billion years, this is the age of the most ancient rocks. What came before, you can only guess and model.

The Paleozoic is only a small interval of the entire geological history.

In total, there are three geological eras: Archaea, Proterozoic and Phanerozoic. The Phanerozoic, in turn, includes the Paleozoic, Mesozoic, and Cenozoic. Scientists study, in particular, the early archaea, when granitoid magmatism arose (granitoids are rocks related to granite). — RT). It was magmatism in the early stages of the Earth's development that was the main geological process that led to the formation of continents. This happened about 3.9 billion years ago.

Magmatism can lead to volcanism, due to which archipelagos of oceanic islands (Hawaiian, Azores, Canary and many others) are formed. With the attenuation of magmatism, the surface sinks, the oceanic islands sink under water, forming underwater ridges, guyots (seamounts. - RT) and other morphostructures of the ocean floor.

Life in the form of the first bacteria began to develop on Earth about 3.9 billion years ago or even earlier. But only about 540 million years ago, it developed so much that skeletal organisms appeared - the ancestors of insects, arachnids and crustaceans.

- There is the hypothesis of an expanding Earth, which assumes that the position and relative motion of the continents is mainly caused by an increase in the volume of planet Earth. What do you think about this?

- Previously, when there was no data and research, it was possible to say that the Earth is expanding, contracting and pulsating. It is now known that the volume of the Earth does not change. When there was no data, there was a lot of fantasy, it's natural.

Now the theory of tectonics of lithospheric plates dominates. On Earth, there are mid-ocean ridges - large underwater rises of the ocean floor at the boundaries of the movement of lithospheric plates.

The lithosphere is the stone shell of the Earth. Under it is a mantle in which convection is possible. As in the kitchen in a boiling pan we see on its surface the movement of some bodies, so approximately the lithospheric plates float along the mantle. Where there are such mid-ocean ridges, there is a split in the lithosphere, which moves in different directions and magma emerges from the mantle, which solidifies and forms the basaltic crust.

• Study of the Mariana Trench
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There are also deep-water trenches, in particular the Mariana Trench, where the well-known Mariana Trench is located. There is a subduction zone – the zone of immersion of the oceanic crust (lithosphere) under another oceanic or continental crust. These two processes form the tectonics of the plates, their movement.

Some scientists believe that the first continent on Earth was formed called Vaalbara, which disintegrated about 3 billion years ago. How did the first continents appear on Earth and what were they? How does the movement of continents affect the planet's ecosystem?

- In geology, there is a concept of supercontinental cycles, according to which supercontinents then formed on Earth, then decayed again. The first supercontinent was formed about 4 billion years ago, later it broke up into several ordinary continents. Subsequently, this cycle of disintegration of a single supercontinent into separate continents was repeated about 2.5 billion, 1.8 billion, 1 billion and about 600 million years ago. The most famous supercontinent - Pangaea was formed at the end of the Paleozoic (about 250 million years ago) and then broke up into the continents already known to us.

It is believed that the decay of the supercontinent occurs due to a convention in the mantle. It is excited by endogenous energy sources, primarily the energy of gravitational forces with a small contribution of energy released during the decay of radioactive elements contained in the bowels of the Earth. Due to a convention in the Earth's mantle or other tectonic forces, continental blocks were assembled into one supercontinent, and then disintegrated in the same way.

Clear examples of the existence of such mantle currents, for example, can be considered the facts of the split of the African continent along the line Red Sea - Gulf of Aden - East African rifts, the pushing of Arabia away from Africa, the expansion of the Atlantic and Indian Oceans, etc.

And since the continents continue to move at a constant speed, in the distant future, supercontinents may form again on Earth.

• Pangaea
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As for the impact of these processes on the climate, since they are very slow, it is difficult to compare them with environmental phenomena. However, it is clear that if there is only one supercontinent on Earth, then the climate will be sharply continental, with large temperature differences. And if there are many continents, then the climate will be more temperate, mild. All this, of course, affects the biosystem: some species go extinct, while others appear.

Recently, there was a devastating earthquake in Turkey and Syria, a series of seismic shocks swept across the planet. What is the reason for this increase in geological activity?

- Geologists operate for millions of years. Those cataclysms that are occurring now are no different from those that were 2-3 billion years ago. This is the usual activity of the Earth. Scientists don't know why seismicity increases or decreases. But the history of earthquakes suggests that their intensity has always been about the same. Man and global warming, which is now much talked about, do not affect the seismicity of the Earth.