How much basic knowledge do you know about our home planet?

This article is based on answering similar questions from netizens, see screenshot:

This kind of common sense is already known in elementary school, but today we can talk about it in more depth. Next, we will share with you the common sense of our home planet from three aspects: the basic situation, structure, and movement of the earth.

Basic Situation

The Earth is a ball with an average diameter of about 12742.02 kilometers and a mass of about 5.97237*10^24 kilograms, or about 600 trillion tons. Why is "about" used here? Because it is impossible to locate the scale and mass of such a large mass object very precisely, and these data themselves change every day, so we can only give an approximate estimate.

Moreover, the earth is not a perfect sphere, it is a little flat, with an oblateness of 0.0033528, so the diameter of the earth is just an average value. The reason why the earth is a little bit not round is that the earth is rotating, and rotating objects have centrifugal force, and the equator is where the centrifugal force is the largest, so the crust near the equator is thrown up a little, and the diameter here is the largest, about 12756 kilometers; while the centrifugal force is the smallest at the poles, so the diameter is also a little smaller, about 12714 kilometers.

This allows us to calculate that the circumference at the equator is about 40,075 kilometers and the circumference at the poles is about 39,942 kilometers.

With these basic data, we can calculate that the total area of ​​the earth is about 510 million square kilometers. Of this 510 million square kilometers, land and islands account for 29.2%, and rivers, lakes, and seas account for 70.8%. Most of the water is marine salt water, with a total volume of about 1.38 billion cubic kilometers, of which 96.5% is seawater.

Of the 13.5% of freshwater resources, more than 99.15% are ice sheets and glaciers. The water resources that can actually be used by humans are in rivers, lakes and reservoirs, which only account for about 0.85% of the total freshwater resources, about 93,000 cubic kilometers. From this we can see that the water resources that can be used by humans only account for 0.0067% of the total water volume.

If all the water on Earth were made into a water ball, the total water ball would be about 1,400 kilometers in diameter, the fresh water ball would be about 270 kilometers, and the usable water ball would only be 56 kilometers in diameter (pictured above). Therefore, the fresh water resources available to humans are very scarce. If humans want to survive in the long term, everyone has the responsibility to conserve water resources.

Earth Structure

The Earth's surface system is composed of the geosphere, hydrosphere, biosphere (including the human sphere), and atmosphere from bottom to top. These belong to the Earth's outer circle and are within the reach of current human activities.

The so-called geosphere is composed of the earth's crust composed of rocks and the soil weathered from rocks; the hydrosphere is the water body covering the geosphere, including oceans, rivers, lakes and streams; the biosphere and anthroposphere are the animals, plants, and microorganisms that live and work on land and in the hydrosphere, especially the traces of human activities that are spread all over the earth.

The atmosphere is the layer of air that covers the Earth, and is the air that humans breathe every moment. Air is mainly composed of nitrogen and oxygen. By volume, nitrogen accounts for about 78%, oxygen accounts for about 21%, and rare gases such as helium, neon, argon, krypton, xenon, and radon account for about 0.934%, carbon dioxide accounts for about 0.04%, and water vapor, dust impurities, etc. account for 0.002%.

Atmospheric density is closely related to temperature and pressure. The atmospheric pressure at sea level is 101325Pa, also known as 1atm, which is 1 standard atmosphere. At 0 degrees Celsius and 1 standard atmosphere, the air density is about 1.293kg/m^2. As the altitude increases, the air pressure will become lower and lower, and the density will become smaller and smaller, that is, it will become thinner and thinner.

The atmosphere is generally divided into five layers, starting from the surface, called the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. There is no strict boundary between the atmosphere and outer space. At tens of thousands of kilometers above the earth, there are still rare atmospheric particles. The radius of the Earth's Hill sphere is 1.5 million kilometers, which means that the range of the Earth's gravitational influence is 1.5 million kilometers, so there are still Earth's atmospheric molecules there.

The inner circle of the earth is mainly the solid part of the earth, mainly referring to the three layers under the crust, namely the mantle layer, the liquid layer outside the core, and the core, which can be further subdivided into the upper mantle, lower mantle, outer core, transition layer, and inner core. This subdivision is because each layer does not change suddenly, but changes gradually.

The average thickness of the crust is about 35 kilometers, with the thinnest being only a few kilometers (trench) and the thickest being more than 70 kilometers (mountain top); the thickness of the mantle layer is about 2865 kilometers; the radius of the core is about 3471 kilometers. From the surface downward, the deeper you go, the higher the temperature and the greater the pressure. The temperature of the mantle is about 1000~2000℃, and the temperature of the core is between 2000~6000℃. The pressure in the core of the crust can reach 3.6 million atmospheres, and the material density is about 12.9g/cm^3.

The details of various parts of the earth have been introduced in previous articles, so I will not repeat them here.

Earth Movement

The movement of the earth is the most worth introducing part of the earth, because it is the movement that gives the earth vitality and life.

The sun occupies 99.86% of the mass of the solar system, and is the natural leader, with absolute control over the solar system. Therefore, the earth, which is only 1/330,000 of the mass of the sun, has been pulled around the sun by the sun's gravity since its birth, just like the other seven planets.

But shortly after birth, the Earth's operating state changed.

The reason for the change is that a planet about the size of Mars collided with the Earth. Scientists called this planet "Theia". As a result of the collision, it merged with the Earth, so that the mass of the Earth increased by about 1/8, and now it is about 600 trillion tons.

This collision not only made the Earth "fatter", but also knocked the Earth's rotation axis crooked. The rotation axis, which was originally perpendicular to the solar ecliptic, was tilted by about 23.44 degrees, so it revolves with its neck tilted.

Not only that, when Theia collided with the Earth, it also knocked off a lot of lava. Under the influence of the Earth's gravity, this lava did not fly far away, but revolved around the Earth for a while, and then condensed into a planet due to gravity, which is the Moon. Since then, the Moon has become the only natural satellite of the Earth, revolving around the Earth for 4.5 billion years.

In this way, the Earth and the Moon formed an Earth-Moon system, and it is this optimal combination that allowed life to appear on Earth. First, the Earth rotates with its neck tilted, causing the position of direct sunlight on the Earth to change periodically, moving up and down around the equator between 23.44 degrees south latitude and 23.44 degrees north latitude once a year. All things grow with the help of the sun, thus forming the climate changes of spring, summer, autumn and winter throughout the year.

The formation of the moon has created a tidal force on the earth that is 2.5 times greater than that of the sun, greatly strengthening the movement of the earth's ocean tides. As the earth rotates, the position of the earth's surface relative to the moon changes and moves all the time, and the ocean will rise and fall with the movement of the moon's tidal force, twice a day. It is the change of seasons and the effect of ocean tides that make the earth full of vitality and promote the evolution of life on earth.

Therefore, the scientific community believes that if there had not been that collision, or if the collision had been more or less, the Earth might have been like Venus and Mars, and life might not have appeared. Therefore, the reason why we exist is thanks to this collision.

Among the eight planets in the solar system, there are four terrestrial planets, which are planets similar to the Earth and have a hard rocky crust; there are four Jovian giant planets, which are similar to Jupiter, mainly composed of gas, have no solid surface, and are huge in size and mass. The four terrestrial planets are closer to the sun than the gas planets, so they are also called inner planets.

The Earth is the largest of the terrestrial planets, with the largest mass and volume. Counting from the closest to the Sun, the Earth ranks third, with an average orbital radius of about 150 million kilometers. The Earth rotates once a day, with a linear speed of about 464 meters per second at the equator; it also revolves around the Sun in an orderly manner, with a linear speed of about 29.783 kilometers per second, and revolves around the Sun once a year, about 365.25 days.

These are the general common sense about the earth. Welcome to discuss and thank you for reading.

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