Planets and Asteroids: What the Earth Was Made of

Formation of the solar system

The Standard Model for the Formation of the Solar System (including Earth)

is the solar nebula hypothesis. According to this theory, the solar system was formed from a large rotating cloud of interstellar dust and gas called the solar nebula.

It consisted of hydrogen and helium createdshortly after the Big Bang 13.7 billion years ago, and heavier elements ejected by supernovae. About 4.5 billion years ago, the nebula began to shrink, possibly caused by a nearby supernova shock.

The shockwave could also be created by rotatingnebula. As the cloud began to accelerate, its angular momentum, gravity and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation. As a result of collisions of large debris with each other, protoplanets began to form, orbiting the center of the nebula.

Matter in the center of the nebula, not having muchangular momentum, compressed and heated, as a result of which the nuclear fusion of hydrogen into helium began. After further contraction, the T Tauri star flared up and turned into the Sun.

Meanwhile, in the outer region of the nebula, gravity caused a process of condensation around the density perturbation and dust particles, and the rest of the protoplanetary disk began to split into rings.

In a process known as accretion, dust particles and debris clump together into larger fragments to form planets. Thus, the Earth was formed about 4.54 billion years ago (with an error of 1%).

This process was largely completed during10-20 million years. The solar wind of the newly formed T Tauri star cleared out most of the matter on the disk that had not yet condensed into larger bodies. The same process will produce accretion discs around virtually all newly formed stars in the universe, some of which will acquire planets.

Proto-Earth has increased due to accretion, while itsthe surface was hot enough to melt the heavy, siderophilic elements. Metals, having a higher density than silicates, plunged into the interior of the Earth.

This iron catastrophe led to the division intoa primitive mantle and a metal core just 10 million years after the Earth began to form, producing the layered structure of the Earth and shaping the Earth's magnetic field.

The first atmosphere of the Earth captured from the solarnebula, consisted of the light (atmospheric) elements of the solar nebula, mainly hydrogen and helium. The combination of the solar wind and the high temperature of the surface of the newly formed planet led to the loss of part of the atmosphere, as a result of which the percentage ratio of these elements to the heavier ones in the atmosphere is currently lower than in outer space.

Geological history of the Earth

Geological history of the Earth - sequenceevents in the development of the Earth as a planet: from the formation of rocks, the emergence and destruction of landforms, the immersion of land under water, the retreat of the sea, glaciation, to the appearance and disappearance of animals and plants and other events of the geochronological time scale. It was created mainly on the basis of studying the rock layers of the planet.

Initial state of the Earth

Initially, the Earth was melted and red-hot due to strong volcanism and frequent collisions with other bodies. But in the end, the outer layer of the planet cools and turns into the Earth's crust.

A little later, as a result of a collision ontangent to a celestial body, the size of Mars and a mass of about 10% of the earth, the Moon was formed. As a result, most of the material of the impacting object and part of the material of the earth's mantle were thrown into near-earth orbit. The proto-Moon gathered from these debris and began to orbit with a radius of about 60 thousand km.

Orbit formation

The ground got sharp as a result of the impact.an increase in the speed of rotation, making one revolution in 5 hours, and a noticeable tilt of the axis of rotation. Degassing and volcanic activity created the first atmosphere on Earth. Condensation of water vapor, as well as ice from comets colliding with the Earth, formed the oceans.

Surface

For hundreds of millions of years, the surfacethe planets were constantly changing, continents formed and disintegrated. They migrated across the surface, sometimes joining together to form a supercontinent. About 750 million years ago, the earliest known supercontinent Rodinia began to disintegrate. Later, from 600 to 540 million years ago, the continents formed Pannotia and, finally, Pangea, which disintegrated 180 million years ago.

The modern ice age began around 40 millionyears ago, and then intensified at the end of the Pliocene. The polar regions have since undergone repeating cycles of glaciation and melting, repeating every 40-100 thousand years. The last ice age of the current ice age ended about 10,000 years ago.

Structure

The bowels of the Earth can be divided into layers according to theirmechanical (in particular rheological) or chemical properties. According to the mechanical properties, the lithosphere, asthenosphere, mesosphere, outer core and inner core are distinguished.

History of the Earth

Modern scientific hypothesis of the formation of the Earthand other planets of the solar system is the hypothesis of the solar nebula, according to which the solar system was formed from a large cloud of interstellar dust and gas. The cloud consisted mainly of hydrogen and helium, which formed after the Big Bang, and heavier elements left behind by supernova explosions.

About 4.5 billion years ago, the cloud becamecollapse, which probably happened due to the impact of a shock wave from a supernova that exploded a few light years away. As the cloud began to contract, its angular momentum, gravity and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation.

After that, the debris in the protoplanetary disk underby the action of gravity, they began to collide, and, merging, formed the first planetoids. Comparison of the sizes of the terrestrial planets (from left to right): Mercury, Venus, Earth, Mars.

During accretion, planetoids, dust, gas andthe debris left after the formation of the solar system began to merge into ever larger objects, forming planets. The approximate date of the formation of the Earth is 4.54 ± 0.04 billion years ago. The entire process of the planet's formation took about 10-20 million years.

The moon formed later - about 4.527 ± 0.01billion years ago, although its origin has not yet been precisely established. The main hypothesis is that it was formed by accretion from matter left after a tangential collision of the Earth with an object close in size to Mars and a mass of 10-12% of the Earth's (sometimes this object is called "Theia").

In this collision, approximately100 million times more energy than the one that supposedly caused the extinction of the dinosaurs. This was enough to evaporate the outer layers of the Earth and melt both bodies.

Part of the mantle was thrown into Earth's orbit, whichpredicts why the Moon is deprived of metallic material and explains its unusual composition. Under the influence of its own gravity, the ejected material took a spherical shape and the Moon was formed.

Proto-earth increased due to accretion, and washot enough to melt metals and minerals. Iron, as well as geochemically related siderophilic elements, having a higher density than silicates and aluminosilicates, descended to the center of the Earth.

This led to the separation of the inner layers of the Earth.to the mantle and metal core just 10 million years after the Earth began to form, producing the layered structure of the Earth and forming the Earth's magnetic field.

Gassing from the crust and volcanicactivity led to the formation of a primary atmosphere. Condensation of water vapor, enhanced by ice carried by comets and asteroids, led to the formation of oceans.

The Earth's atmosphere then consisted of lungsatmospheric elements: hydrogen and helium, but it contained significantly more carbon dioxide than it is now, and this saved the oceans from freezing, since the luminosity of the Sun then did not exceed 70% of the current level. About 3.5 billion years ago, the Earth's magnetic field was formed, which prevented the devastation of the atmosphere by the solar wind.

The surface of the planet was constantly changing inover hundreds of millions of years: continents appeared and collapsed, moved along the surface, periodically gathering in a supercontinent, then diverging to isolated continents.

So, about 750 million years ago, a singleRodinia, then its parts merged into Pannotia (600-540 million years ago), and then - in the last of the supercontinents - Pangea, which disintegrated 180 million years ago.

The appearance of the moon

Relatively large natural satellite of the Earth,The moon is larger in relation to its planet than any other satellite in the solar system. During the Apollo program, rocks were brought to Earth from the lunar surface.

Radiometric dating of these rocks showedthat the Moon is 4.53 ± 0.01 billion years old, and it originated at least 30 million years after the solar system was formed. New data indicate that the moon was formed even later, 4.48 ± 0.02 billion years ago, or 70-110 million years after the emergence of the solar system.

Theories of the formation of the moon should explain its late formation, as well as the following facts.

First, the Moon has a low density (3.3 times that of water, compared to 5.5 for Earth) and a small metallic core.

Secondly, there is practically no water or other volatile matter on the moon.

Third, the Earth and the Moon have the sameisotopic signatures of oxygen (relative abundance of oxygen isotopes). Of the theories that have been proposed to explain these facts, only one has gained widespread acceptance: the giant collision hypothesis suggests that the moon came about as a result of a Mars-sized object hitting proto-Earth with a glancing impact.

The collision of this object, sometimes called Theia, released about 100 million times more energy with the Earth than the impact that caused the extinction of the dinosaurs.

It was enough to vaporize someouter layers of the Earth and the melting of both bodies. Part of the mantle was thrown into orbit around the Earth. This hypothesis predicts why the Moon was deprived of metallic material and explains its unusual composition.

The substance thrown into orbit around the Earthcould condense into a single body within a few weeks. Under the influence of its own gravity, the ejected material took a spherical shape, and the Moon was formed.

New theories of the composition of the earth

Scientists from Arizona State University (ASU) have prepared an article in which they outlined a new rationale for the hypothesis of an unthinkable catastrophe from the distant past of the Earth, during which the Moon appeared.

It is assumed that more thanthe dense, but smaller planet Theia. The piece that broke away from the Earth or Theia became the Moon, and the remnants of Theia scattered through space or plunged deep into the Earth, as researchers from the United States are trying to prove.

The theory of the impact of the appearance of the moon is not new, asand the idea of the appearance within our planet of large regions with a low shear rate - two giant anomalies inside the mantle on the surface of the Earth's outer core.

But these are only hypotheses for which there is nodirect evidence. Scientists from Arizona State University are confident that their new calculations have significantly added weight to the hypothesis of the alien origin of anomalies in the Earth's mantle.

The density of the hypothetical planet Theia is significantexceeded the density of the ancient Earth, so its iron-rich large fragments gradually sank to the core of our planet. One such fragment is located under Africa, and the other under the Pacific Ocean. Researchers study the seismic behavior of these anomalies and state their difference from the behavior of other terrestrial rocks. According to new simulations of the behavior of the anomalies, it fits into the theory of a collision with the Earth of a smaller planet, but with a 6% higher density.

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