HistBio — 04. Origin of the Solar System and Earth

An interesting exercise is to try to look at our planet (and the Solar System, which includes Earth) from the outside.

Compared to the Universe, our Earth seems tiny, and for the biosystems we perceive directly, it is incomprehensible. However, Earth life is an integral part of our planet. The properties of Earth life are largely determined by the properties of the Earth. The Earth is inextricably linked to the Sun. The origin of the Earth and the Sun can be imagined in different ways. Jokes aside, this is an important event that determined the properties of Earth's biosystems.

Our Earth is part of the Solar System and originated at the same time as it. Strange as it may seem, by that time, most of the history of our Universe had already passed. Note the scale gap! The Solar System formed from a cluster of matter, partly left after the destruction of previously existing stars, and partly constituting the most common material in the Universe – hydrogen. Gravity gathered this matter together; after its accumulation in the center of the condensing nebula, a new star ignited. Its stable state is a consequence of the balance of two opposing processes: gravity gathers the star's matter together, compresses the nuclei, and promotes thermonuclear reactions, during which a helium nucleus is formed from two hydrogen nuclei, and the energy released "scatters" the star's matter, preventing further thermonuclear reactions. The energy released during thermonuclear reactions is transferred within the Sun until it reaches its outer shell, which radiates it into cold space in the form of a stream of electromagnetic radiation.

Part of the cloud material from which the Solar System formed had a sufficiently high momentum. When a star ignited in the center of the cloud, this part of the matter, under the influence of its momentum, remained rotating around the center, forming a protoplanetary accretion disk. As a result of the self-organization process, planets formed from this disk. The formation of planets from an accretion disk is a process that can be computer-modeled. The images below illustrate the processes occurring in these models. One of the surprising results of the modeling is this: for planets made of solid material to form, the cloud particles must begin to stick together, forming clusters whose gravity will attract new matter. For this to happen, the material of the protoplanetary disk must be "sticky." What substances could provide this sticking? The answer, in the broadest sense, is: organic matter! In other parts of the course, we will discuss that the origin of organic compounds does not require any special terrestrial conditions at all. Organic matter forms massively in space as well. As a result of the sticking of fragments of the protoplanetary disk, clusters of matter form. Initially, this matter is cold, just as the entire cloud from which the Solar System formed was cold. The Sun heated up due to thermonuclear reactions, but it could not effectively heat the planets. Nevertheless, initially cold planets heated up.

{ "title": "The Earth and the Solar System", "summary": "The Earth is part of the Solar System and was formed simultaneously with it. The Solar System was formed from a cloud of matter, partially left over from the destruction of earlier stars, and partially consisting of the most common substance in the universe - hydrogen.", "body": "An interesting exercise is to try to look at our planet (and the Solar System, which includes Earth) from the side. [IMG_1] By comparison with the Universe, our Earth seems tiny, and for those biosystems that we perceive directly - it is immense. However, Earth's life is an integral part of our planet. The properties of Earth's life are largely determined by the properties of the Earth. The Earth is inextricably linked with the Sun. The origin of the Earth and the Sun can be imagined in different ways. Jokes aside, but this is a crucial event that determined the properties of Earth's biosystems. [IMG_2] Our Earth is part of the Solar System and was formed simultaneously with it. As surprising as it may seem, by that time, most of the history of our Universe had already passed. [IMG_3] Note the scale break! The Solar System was formed from a cloud of matter, partially left over from the destruction of earlier stars, and partially consisting of the most common substance in the universe - hydrogen. Gravity gathered this matter together; after its accumulation in the center of the concentrating nebula, a new star ignited. Its stable state is a consequence of the equilibrium of two opposing processes: gravity gathers the star's matter together, compresses the nuclei, and promotes a thermonuclear reaction, in which a helium nucleus is formed from two hydrogen nuclei, and the energy released in this process \"scatters\" the star's matter, preventing further thermonuclear reaction. The energy released during the thermonuclear reaction is transferred within the Sun until it reaches its outer shell, which radiates it into the cold cosmos in the form of a stream of electromagnetic radiation. [IMG_4] Part of the material of the cloud from which the Solar System was formed had a sufficiently high impulse. When the star ignited in the center of the cloud, this part of the matter, under the influence of its impulse, continued to rotate around the center, forming a protoplanetary accretion disk. As a result of the self-organization process, planets were formed from this disk. [IMG_5] The formation of planets from the accretion disk is a process that can be modeled using computers. The illustrations below show the processes that occur in these models. [IMG_6] One of the surprising results of modeling is that in order for planets consisting of solid matter to form, the particles of the cloud must begin to stick together, forming clusters, the gravity of which will attract new matter. For this, the material of the protoplanetary disk must be \"sticky\". What substances could provide this sticking? The answer, in the broadest sense, is: organic matter! [IMG_7] In other parts of the course, we will discuss that the emergence of organic substances does not require any special Earth conditions. Organic matter is massively formed in space as well. As a result of the sticking of fragments of the protoplanetary disk, clusters of matter are formed. Initially, this matter is cold, as the entire cloud from which the Solar System was formed was cold. The Sun was heated due to thermonuclear reactions, but it could not effectively heat the planets. Nevertheless, the initially cold planets warmed up. To some extent, the source of heating of our planet was the radioactive decay of heavy elements in its composition. However, a much larger amount of energy was associated with the gravitational differentiation of the planet's matter. In the initial material of the planet, relatively heavy components (metals) and lighter substances (various oxides of non-metals) were mixed. Gravity gathered them together; if some local process (for example, heating during a collision) led to the melting of part of the matter, the heavy components moved down, to the center of gravity, and the light ones rose up. During this process, a huge amount of energy was released (the potential energy of the heavy components removed from the center of the planet was converted, ultimately, into heat). As a result, the entire planet warmed up and melted. A hot metal core was formed in the center of the planet. The outer core is liquid (due to heating), and the inner core, although it is even hotter, is solid due to the colossal pressure it is under. [IMG_8] The current heat of the Earth's interior is the same heat that was released during the gravitational differentiation of the Earth's interior. The Earth is so large that it simply has not had time to cool down since its birth! And it will not have time to. The Sun is at the midpoint of its \"life path\" in its current phase; after the end of this phase, it will significantly increase in volume, and its outer boundary will reach the current Earth's orbit. The Earth will heat up, its movement will be stopped due to interaction with the Sun's outer shells, and its matter will finally become part of the star. But even before that time, the Earth's interior will retain the energy of gravitational differentiation from the time of its birth. Various processes lead to the slowing down of the Earth's rotation around its axis. For example, one of them is tides, which affect not only the ocean but also the Earth's crust. The Earth's crust bulges in the direction of the Moon when it is above a particular part of our planet, and subsides downward when the Moon moves away (more precisely, when the Earth rotates under the Moon). A significant amount of energy is spent on these processes. This slows down the rotation of the crust. Do you know how to determine if a chicken egg is raw or boiled without breaking it? You need to spin it and then suddenly stop it with your hand. A raw egg will continue to rotate (naturally, with a lower speed) after your hand is removed. A boiled egg will remain stationary. The reason is that in the case of a raw egg, we are braking the movement of the solid shell, and the dynamically connected semi-liquid contents continue to rotate. The processes that slow down the Earth's movement act on the crust. The solid inner core in the viscous outer core begins to rotate. This rotation occurs in the initial magnetic field, which is quite weak. The movement of magnetized bodies (and the core has magnetic properties) in a magnetic field causes electric currents in closed circuits (the dynamo effect). These electric currents lead to a sharp increase in the magnetic field. The details of the electric currents in the core and their connection to the Earth's magnetic properties are still being studied. However, for us, it is important that the presence of a powerful magnetic field on our planet, which protects its surface from ionizing radiation, is a consequence of the fact that the Earth has an extremely large satellite that has slowed down the movement of its crust. The video you just watched links the origin of the Moon to a planetary collision. The reason is that the size ratio of the Earth and the Moon is very unusual for celestial bodies and satellites: the Moon is very large. Data on the chemical composition of the Moon, obtained by the Apollo expeditions, showed its extraordinary similarity to the Earth. These features are well explained by the impact (collision) hypothesis of the Moon's origin, proposed in 1975 by William K. Hartmann and Donald R. Davis. Modeling of the impact shows that it must be precisely calculated, like a billiard player's shot. How could this have happened? One of the plausible options is as follows. The great French astronomer, mathematician, and mechanic Joseph Lagrange proved in the 18th century that in a system of two bodies, there are five points (Lagrange points) where their influence on a third body is balanced. If body A rotates around body B in an orbit, one of these points is on the orbit of body A ahead of it, and the second is on the same orbit behind body A. So, it can be assumed that Theia, which was smaller than the Earth, was in one of the Lagrange points on the Earth's orbit. This is a stable state, but some impact (for example, a meteorite impact) could have knocked Theia out of that point, where it did not feel the Earth's gravity. The result was a planetary collision. This process can be modeled. In any case, the Moon, in its structure, resembles the Earth, except that it has already cooled down. Note that the Moon's core is relatively small. It can be said that the Moon is depleted of iron compared to the Earth. The reasons for this difference are not yet fully understood. [IMG_9] So, the Earth (or rather, life on Earth) was lucky to have a satellite. It is interesting to compare the Earth with other planets in the Earth's group. This question is discussed in more detail in the corresponding section of the ecology textbook. This is a diagram of the structure of Venus. You can see that it is very similar to the Earth in terms of size and structure. Unfortunately, as a result of the accumulation of carbon dioxide in the atmosphere of Venus, it has become a very inhospitable planet. [IMG_10] This is a reconstruction of the surface of Venus. [IMG_11] And this is Mars. A planet similar to Earth, but already cooled down. [IMG_12] Its structure also resembles that of the Earth, except that its core has already solidified. [IMG_13] This is a photograph of the Kandor canyon in the Mariner Valley on Mars. [IMG_14] Gullies on Mars. [IMG_15] Sedimentary rocks at the bottom of a crater on Mars. [IMG_16] Traces of flowing water on Mars. [IMG_17] Martian landscape of frozen carbon dioxide. [IMG_18] And this is a dust-covered ice plain on Mars with signs of meteorite bombardment. [IMG_19] It is interesting to compare the Earth not only with planets in the Earth's group but also with satellites of larger planets. This is the surface of Europa, the sixth satellite of Jupiter. Europa has a silicate surface and an iron core. The surface of the satellite is covered with water ice, under which, probably, there is liquid water! [IMG_20] And this is a photograph of the surface of Titan, a satellite of Saturn. It has a dense atmosphere. The surface of Titan consists of frozen water and sedimentary organic matter. There are even cryovolcanoes on it! On Titan, there are methane rains that fall from methane clouds. Methane sediments accumulate in rivers, which flow into methane seas. In 2005, Titan was surveyed by the American Cassini station, which even sent a probe called Huygens to its surface. [IMG_21] This is a computer reconstruction of the shore of a methane sea on Titan. [IMG_22] Do the landscapes of other celestial bodies seem familiar to you? This is because they were formed by forces similar to those that formed the Earth..." }