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105 We got a double jolt in 1994. In February, a small asteroid, about 10 meters across, exploded in the atmosphere over the western Pacific Ocean in a blast 10 times as powerful as the Hiroshima A-bomb. Surveillance satellites alerted U.S. officials; thinking that this explosion might have been nuclear, they reportedly awakened the President. In July of that year, astronomers watched the fragments of Comet Shoemaker-Levy plow into Jupiter’s atmosphere, leaving scars that per- sisted for months. American legislators directed NASA and the Depart- ment of Defense, in coordination with the space agencies of other countries, to identify and catalog within 10 years the orbital characteristics of all comets and asteroids that are greater than 1 kilometer in diameter and whose orbits cross that of the Earth. That led to the Spaceguard Survey, foreseen by Arthur Clarke in his 1973 novel Rendezvous with Rama. A more modest program known as Spacewatch had been operating since the 1980s. Already, the Spaceguard Survey has found over 700 Near Earth Objects with a diameter of 1 kilometer or more; one may strike the Earth every 500,000 years (the frequency is much higher for smaller bodies). Studies have indicated that the impact of a comet or asteroid serious enough to precipitate the collapse of civilization may occur every 100,000 to 300,000 years.” Our improved detection capabilities have enabled us to spot smaller asteroids, including some that pass closer than our Moon. Astronomers discovered in 2004 that a 1000-foot-wide object will narrowly miss the Earth in 2029, possibly at a lower altitude than the communications satel- lites we place in geosynchronous orbit. If that small asteroid hit the Earth, the impact energy would be 850 megatons—15 times more powerful than the largest hydrogen bomb ever tested and 60 times more devastating than the Tunguska blast that leveled vast areas of Siberian forest in 1908.°° The danger is not entirely predictable, as asteroids dislodged from their presently “safe” orbits could penetrate into the inner solar system. There may be more than 700,000 asteroids larger than 1 kilometer across—the threshold for global catastrophe.” The possible effects of large-body impacts have sensitized the scientific community to think more in terms of cosmic influences on Earth systems. As Jill Tarter observed, we have recently begun to appreciate how inti- mately the evolution to intelligent life on Earth was connected with our astrophysical environment. Giant impacts almost certainly introduced a random extraterrestrial factor into the history of life, punctuating evolutionary change. Seeing the Earth as being predominantly under the control of cosmic influences, geologist Michael Rampino proposed an alternative to the Gaia theory: the “Shiva Hypothesis,” named for the Hindu goddess of destruction who returns all forms back into the primordial nature from which they emerged.” Extraterrestrial Terminators