Earth - our home planet

Earth-Moon Partnership

The image above was taken by the Galileo spacecraft on its way to Jupiter. Both the Earth and Moon appear as crescents. Click to enlarge. Can you work out where the Sun was?

Air To Breathe

The atmosphere is composed mainly of nitrogen (78%) and oxygen (21%), with small traces of other gases. These proportions remain fairly constant up to around 80km, but the heavy gases become rare at greater heights and only hydrogen and helium are found in the outermost regions.

Fig. 1: The Thin Atmosphere

25km above the surface, a concentrated layer of ozone (O₃) exists. This ozone layer is vital to life on the planet, as it stops nearly all of the Sun's harmful ultraviolet radiation from reaching the surface. Scientists believe that we have been damaging it, increasing the risk of skin cancer.

The Earth's atmosphere contains a large amount of water vapour, although its concentration varies, and depends on the time of the year. Most is visible as clouds, extending no higher than 13km. It is in this region that the dominant weather systems are found. Above this lies a layer of warm air which holds cooler air below containing most of the water vapour, and the clouds that we see.

Click for a LIVE satellite image of Europe's weather!

Beauty in the Skies

Longitude!

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Cloudless Earth?

The Pull of Gravity

Until Newton, no-one had any real idea as to why we all walk around on the surface of the Earth, held in place by an invisible force. Newton showed that not only does it hold us in place, but it also holds the planets in orbit around the Sun.

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Active Surface

The surface of the planet has much geological activity, and is shaped by continental drifting (plate tectonics). This makes the surface relatively young. Combined with other factors, such as the atmosphere and weathering, it explains why few visible impact craters can be found. The heavily cratered surface of the moon gives a more accurate guide as to the quantity of collisions with debris making its way through the solar system. Here, surface features date back to the formation of the solar system, and have remained undisturbed due to the moon's geological inactivity.

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The structure of the planet itself is divided into three regions: the crust which extends for roughly 7km beneath the oceans and 40km beneath the continents; the mantle which is roughly 2870km thick; and the core which accounts for the remaining 3480km.

The core is composed of two layers: the inner is solid; the outer flows. They are both composed mainly of iron, and it is convection in the molten outer layer that plays an important role in accounting for the planet's magnetic field. Interestingly, the magnetic field reverses every million years or so; north becoming south, and vice versa.