During its life span, our planet has suffered the impact of close to 30 small planets, up to 10 miles in diameter and travelling 60 times the speed of sound. Each such impact releases about a thousand times as much energy as would be released if all the nuclear powers exploded all their present weapon stocks.
About 5,000 giant meteorities with diameters of more than a kilometre have hit the Earth over the past 600 million years, with an average strike rate of one per 120,000 years. Meteorites with diameters greater than 300 metres have hit the Earth once in every 10,000 years.
About once every century a similar object can be expected to travel past Earth. And once in every 250,000 years, on an average, the Earth and such a body will collide. The impact of the collision will release energy equivalent to 10,000 megaton hydrogen bombs and will make a crater some 20 kilometres in diameter.
In 1937, a body about a kilometre in diameter, later named Hermes, passed within 800,000 kilometres of the Earth, no more than twice the distance of the moon. It has not been seen again.
Such events can also destroy up to 90 per cent of all living organisms, from the microscopic to the macroscopic. The impact makes the Earth ring like a bell, and its impact may be felt by the planet for may be a million years or more.
Thankfully, most of these intruders burn themselves out as ‘shooting stars’ in friction with our air. But due to the shower of meteoric materials, chiefly dust, falling from the sky, the Earth’s weight increases by about 100,000 pounds each year.
These interesting facts come from the ‘Woodpecker volume 2000’, an annual compilation on the state of the planet, published by the Academy of Mountain Environics, an NGO based in Dehradun, in north India.