When speaking of cosmic collision, one great enough to cause an extinction level event, often termed E.L.E. occur every 100 million years on average. Therefore, we might not expect such event to happen during the coarse of human evolution. Despite such small odds, much effort should be made to prevent such disaster. Should such rare object from outer space hit Earth, humans along with about 40 percent of all life will disappear in a cosmic blink of an eye!

Collisions do happen regulary! Have you ever seen a shooting star? The Earth's atmosphere is able to burn up anything smaller than 30 feet in diameter. Larger collisions resulting in the likeness of the Barringer Crater in Arizona, USA, happens about every 1000 years. Asteroids in the 1 kilometer range will hit about every 500,000 years. Craters can rarely be seen from collisons because the Earth is seventy percent covered with water. Additionally, being the most geologically active of the inner planets of the solar system, craters will erode away in short periods of time.

One might ask how often people get killed from asteroids. The ancient Chinese have recorded a few incidents of such deaths making maybe 2 or 3 people known. Since people and man made objects occupy a very small percentage of Earth's surface, the odds are astronomically small. How many people won the state lottery 9 times? :-)

In order to better understand cosmic collisions, explorations to Luna and Mars would be necessary. This can usaully be done via advance robotic probes. With Luna not having an atmosphere, craters are well preserved from the early days of the solar system. Mars however will provide better understanding since there is minimal geological changes.

Additionally, federal and private grants alike should be invested in locating Near Earth Objects (NEO). Locating, tracking, and preparing planetary defenses against NEOs would cost each person on Earth about 25 cents a year through the year 2030. Planetary defenses would typically include space platforms orbiting about 1 million kilometers from Earth sporting space telescopes, robotic probes, and nuclear warheads.