Introductory text to the planet Earth
The earth is the third planet in the solar system and at the same time the only celestial body on which life could be proven. As the fifth largest planet, the earth orbits in 365 days and six hours the sun on an elliptical track. One day lasts 23 hours, 56 minutes and 4 seconds. This corresponds to the time that the planet needs for a complete self-rotation, or in other words, to turn around on its own.
On Earth, temperatures range from -89 ° C to + 58 ° C, which are the absolute extremes. The mean air temperature is approx. + 15 ° C. Thus, it lies in a - for the development of life - optimal temperature range. Because the axis of rotation of the earth is inclined by 23.5 °, solar rays reach the different latitudes at a different angle of incidence. The steeper the sun's rays hit the earth's surface, the more radiant energy is released. The angle of inclination of the axis of rotation is responsible for the emergence of the seasons.
With the moon, the earth has a faithful companion. One speaks also of the Erdtrabanten (Trabant = companion). According to the now common theory, collided in the early phase of the solar system, a protoplanet with the earth. The enormous impact threw rock material into orbit, which formed the moon within a short time. Today, the moon is about one quarter of the Earth's mass.
In addition to the solar and lunar eclipses, the moon is also responsible for the tides on Earth. While the Trabant revolves around the earth, its gravitational pull causes the mass of water to shift. Furthermore, the moon stabilizes by its gravity, the axis of rotation of the earth. Without the moon, the Earth's axis would fluctuate more, with the result that temperatures on Earth would become noticeably more extreme, both in the minus and plus ranges. For the development of life on earth, the moon should have played a not to be underestimated role.
The atmosphere of the earth
Compared to all other planets in the solar system, the Earth has an atmosphere of sufficient oxygen. About 21% of the earth's atmosphere consists of oxygen, whereas nitrogen accounts for the largest share with 78%. Originally there was no oxygen in the Earth's atmosphere. Only photosynthesizing cyanobacteria and later also plants enriched the atmosphere with oxygen through their metabolism. The process of photosynthesis is about 3.8 billion years old and has enabled a life in its present form.
The atmosphere has another important role to play. Billions of small meteorites enter the Earth's atmosphere every day and burn up. Without atmosphere the earth resembled a permanent theater of war, as it would be exposed to the constant meteorite impacts. Only very large meteorites or asteroids reach the earth's surface without completely burning up. Most recently, an asteroid struck in 1908 in Siberia (Tunguska event) and destroyed an area of 2100sqm. The explosive energy exceeded that of the atomic bomb dropped by Hiroshima by more than a thousand times. Even in 7000km away Central Europe, the pressure wave was felt.
The earth (k) a bullet?
The earth is not a perfect sphere, even if the view from space suggests it. At the north and south pole, the earth is flattened due to the lack of centrifugal force (earth flattening). At the equator, the centrifugal force develops its maximum and pushes the earth mass slightly to the outside. In contrast, both ends of the axis of rotation (north and south pole) are not affected by the centrifugal force. This results in an interesting effect on our weight: Due to the lack of centrifugal force at the poles, a human weighs about 0.5% more at the north or south pole, as if he were standing at the equator. Because the centrifugal force counteracts the attraction of the earth and just the centrifugal force is missing at the ends of the axis of rotation. In addition, the distance at the poles to the center of the earth is less than from the equator to the center of the earth. The closer we are to the center of the earth, the greater the gravitational force of the earth. Because of the Erdabplattung one is therefore, compared to the equator, at the poles a little closer to the center of the earth.
The habitable zone
As the only planet in the solar system, the earth lies in the habitable zone. We call the tolerable distance of a planet to its star habitable zone, if water can permanently exist in a liquid aggregate state. The following conditions must be met: First, the planet must not be too far from its sun, otherwise the water would freeze. Second, the planet must not be too close to its sun, otherwise the water evaporates. The temperatures should therefore be in a range of 0 ° C to 100 ° C, optimally permanent. Of course, there are other prerequisites, such as that the planet must exist long enough for complex life to develop. And last but not least, water must be present on a habitable planet, at least for earth-like creatures. The water most likely came to Earth through asteroids.
In the solar system, apart from the earth's moon, only Mars as a 'living space' would come into consideration for us humans. However, only with very high technical effort, because lack of oxygen and temperatures between -130 ° C and + 30 ° C are for us under normal circumstances anything but habitable.
Data and facts about the earth:
The entire earth's surface corresponds to a size of 510,000,000 km². The view from space reveals why the earth, which is about 4.6 billion years old, is known as 'the blue planet'. 29% of the earth's surface is land (150,000,000 km²), and 71% is covered with water (360,000,000 km²). The lowest point is in the Mariana Trench at about 11,000m depth. In contrast: Mount Everest with its 8.845m is the highest attainable point over the sea level. Because of gravity, much higher mountains are excluded in the future. The dead weight or increasing weight prevents mountain massifs that go far beyond this height.
Divided by climatic zone, the following distribution pattern results on the earth: Polar regions: 15%, cold temperate zone: 10%, hot temperate zone: 20%, subtropics: 20%, tropics: 30% and other climatic zones: 5%.
The earth consists of approx. 30% iron, 30% oxygen, 15% silicon and 15% magnesium, whereby the chemical elements on the earth rarely occur in their pure form. Mostly they are in a chemical compound. For example, sand for the most part consists of silica (SiO 2)2).