An interesting fact about Earth is that its speed of rotation is gradually decreasing (Stokes 1982). We already know this truth because few organisms preserved in the fossil, such as mollusks and corals, lay down layer of material on a daily basis. Most of the organisms show variation in its annual growth rate that facilitates geologists to calculate the number of layers in an annual cycle of growth. This transforms directly into the number of days at the time that the organisms were alive. Many organisms show a cyclical pattern of reflecting lunar. These patterns in the fossil record are known as varves. On the basis of the above information, the number of days in a year has been decreasing for various points of time in the geological past. For example, during the Silurian period (about 420 million years ago) there were 420 days in a year; there were 390 days per year in the Carboniferous period (300 million years ago); 370 days per year in the Cretaceous period (80 million years ago). Today we only have 365.25 days in a year. The number of days is still shortening in every 16 million years.
Another interesting fact about Earth is that asteroids have frequently impacted here over the geological time — the larger asteroids have been the reason for mass extinction. The small asteroids (five to ten meters wide) enter Earth’s atmosphere once a year. These relatively small intruders can release the same amount of energy during its entry as the energy release during the atomic bomb dropped on Hiroshima. In 1908, a large comet fragment with a diameter of more than 50 meters, exploded over uninhabited forest area in the Tunguska valley, central Siberia at an altitude of 3–6 miles (5–10 kilometers). This Tunguska explosion is estimated to have been thousand times as powerful as the Hiroshima bomb blast. It burned and crushed the forest to a distance of 30 miles (50 kilometers). Such asteroids almost certainly hit the Earth once every 1000 years.
The other exciting fact about Earth is its age. Expert estimates around 4.54 billion years. But this is not the exact since no earthly materials have been shown to be that much old. The oldest minerals that have been dependably dated are zircon crystals. They are about 4.4 billion years old. So it’s secure to say that the Earth is at least that much old. It is believed that initially the Earth was too hot to support living creatures. However, the most basic traces of life are stromatolites (fossil bacterial colonies) dated to 3.9 billion years ago. This is about 500 million years after the earliest known earthly minerals. It is not sure whether the life first arose on earth or came from elsewhere — may be in the form of bacteria or micro organisms entrenched in an icy meteorite.