END OF HUMAN ERA :Earth will go crazy,i.e. Earth's spin axis will begin to fluctuate chaotically.Hence Life on the Earth will dissapear altogether in a billion years from now ! How read on and inform all your freinds who have this common question.We know that the Earth is spinning once in 24 hours about an axis inclined at an angle of 23.5 degrees with respect to the normal to its orbit around the Sun.The orientation of this axis is preserved as the Earth goes round the Sun an this consistency in tilt is responsible for the seasons on the Earth.The constancy in the orientation of the spin axis is due to the gravitaional effect of the MOON on the Earth.The Earth is bulged at the equator due to its spin. As the planets move in their orbits the net torque varies erratically. A small disturbance in obliquity today will result in a very large change a million years from now.Do you know friends in absence of the MOON this axis would have wandered chaotically from 0 degress to 85 degress. In such a situation it would not have been possible for life to evolve on this planet.In the presence of the MOON's gravitational force together with that of the Sun,the spin axis precesses in a small circle once in every 26,000 years.
In this interval, the tilt of the axis changes by a small amount of 1.3 degrees only. It is important to mention here that the MOON has not been in the same orbit since the begining.As a result of its gravitational interaction with the Earth there is tidal torque which retards the Earth's rotation.This leads to a gradual drifting away of the MOON from the Earth at the rate of nearly 2.5 cm per year In about a billion years the MOON's pull on the Earth will be so weak that the Earth's spin axis will begin to fluctuate chaotically. Hence Life on the Earth will dissapear altogether in a billion years from now. So we ultimately owe our own existence to an important gravitational effect of our beloved MOON on our beloved planet, Earth..