ABSTRACT
The Earth is the largest and most massive of the inner group of planets. In the Solar System, only the Earth is suited for advanced life of our kind; it lies in the middle of the ‘ecosphere’, the region round the Sun where temperatures are neither too high nor too low. The Earth–Moon system is often regarded as a double planet rather than as a planet and a satellite. Below the lithosphere comes the mantle, which extends down to 2890 km and contains 67% of the Earth’s mass. The age of the Earth is approximately 4.6 thousand million years. The Earth has a fairly strong magnetic field; at the equator it is 0.305 G. The impact of the solar wind on the magnetopause compresses the magnetosphere on the day side of the Earth, while the field lines facing away from the Sun stream back to form the magnetotail.
