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1.6. Characteristics of the Earth

Situation of the Earth in the Solar System

The Earth is a rocky planet divided into several layers: crust,  mantle and coreIt is surrounded by a gaseous mass called the atmosphere.

The Earth is located 150 million kilometers away from the Sun. At this distance it is known as astronomical unit.


Earth's surface temperature

The Earth is located at a distance close enough to the Sun so that its rays can heat the Earth's surface, but far enough so that the solar wind pulls it out of the Earth's gravitational field, as happened on Mercury.

The atmosphere allows the energy that comes from the Sun to be distributed over the earth's surface. If it weren't for the atmosphere, the poles would have much colder temperatures and the equatorial zones much warmer, in addition to preventing heat from being lost at night.

Presence of a layer of liquid water: the hydrosphere

Water is very important for living beings, since in addition to being the most abundant chemical substance in living beings, it is the environment in which many of them live, and in which the reactions necessary for life take place.

In addition, the hydrosphere is a great thermoregulator, since it captures and loses heat much more slowly than the ground, thus softening the temperatures of the different areas of the Earth.

The water is in three states: liquid , solid and gaseous.

The Earth is constantly changing

The Earth is a planet that is continually changing continuously since its inception and will continue in the future.

The energy it contains within it is manifested when there are sudden changes, such as those that occur in an earthquake or when a volcano erupts, but also when other slower changes occur, such as those that displace the lithospheric plates that move continents or generate mountain ranges.

But changes are also produced by external processes, such as wind, rain, etc., which also cause the relief to change.

Appearance of life on Earth

The Earth was formed 4.5 billion years ago. The Earth was a ball of fire from which, little by little, the gases that emerged from its interior formed the atmosphere and the hydrosphere. It took about 1 billion years for it to be a suitable planet for life, and 3.5 billion years ago living things emerged.

These living beings fulfilled the three vital functions:

  • Nutrition: They fed and grew taking substances from the environment.
  • Reproduction: They could self-replicate, forming beings similar to themselves.
  • Relationship: They adapted and responded to the needs offered by their environment.

Living beings had the ability to evolve into other more complex forms, up to the current plants and animals.

Why could life appear on Earth?

When the Earth originated from meteorites and planetesimals that clustered together as the Solar System formed, life on Earth was not possible. The earth's surface was covered by lava and gases, which later formed the atmosphere and the hydrosphere.

About 3.5 billion years ago, the surface cooled and solidified. From the water and the components of that primitive atmosphere, and using the energy from the Sun and from the interior of the Earth, the first living beings could emerge. The appearance of living beings caused the composition of the atmosphere to change. These first living beings evolved to current beings.

The appearance of the atmosphere was key to the emergence of life on Earth for several reasons:

  • The atmosphere acts as a protective shield that prevents harmful radiation from the ground from reaching the Earth's surface.
  • The atmosphere generates a greenhouse effect that causes the average temperature to be about 15ºC, instead of the -18ºC that it would have if the atmosphere did not exist, which would make life unviable. In addition, this allows water to exist in a liquid state, essential for living beings because it is part of their composition and the environment in which many of them live.
  • The atmosphere distributes heat from warm to cold areas. In this way, the temperatures are softened making the temperatures not extreme.
  • The atmosphere contains O2 and CO2, necessary for the nutrition of living beings.

In the Biosphere Theme we will return to see the characteristics that make the Earth a habitable planet .