|MadSci Network: Astronomy|
It is hypothesized that a large object impacting the Earth from space, a comet or an asteroid or ?, would throw enough material into the atmosphere to cut-off the sunlight for a long time (perhaps several years). This would cause the Earth's surface temperature to decrease dramatically and would mean that no food could be produced. Without food, humanity will vanish from the Earth.
Modeling has indicated that a 1 km diameter comet impacting the Earth would produce a blast equivalent to 3 Gigatons (3000 millions tons) of high explosives, Comet Impact Simulations. It does not really matter if the object hits land or the ocean. If it hits land, the explosion will immediately eject both Earth and cometary materials into the atmosphere. The upper winds will dispurse this dust so that all of the Earth is affected. If it hits the ocean, the explosion will throw water and cometary material and ocean bottom material into the atmosphere and the winds will distribute them. In addition, a large object hitting the ocean will create a tidal wave perhaps 300 meters high (approximately 1000 feet) which will destroy everything (!) on the coastline.
You can find much material using any of the WWW search engines with the key words "comet" and "impact". An excellent place to start is Spacelink at Marshall Space Flight Center. Other interesting information can be found at:
John Haberman, Space Scientist
NASA/Goddard Space Flight Center
Try the links in the MadSci Library for more information on Astronomy.