[SunkenCiv]

Oddly enough, the Chicxulub crater was discovered about 1960, and something similar to the Alvarez theory was suggested in 1970 (and that may not have been the first, for all I know). The K-T boundary impact first came to the forefront circa 1980 (perhaps it was 1978?), and the candidate crater was suggested to the elder Alvarez by one of the Pemex guys involved in the 1960 study. He heard nothing back, and it was some years before Chicxulub was recognized as the smoking gun.

Nemesis, the Sun's companion star, 1983-present
The Nine Planets
"Hypothetical Planets"

This hypothetical "death companion" of the Sun was suggested in 1985 by Daniel P. Whitmire and John J. Matese, Univ of Southern Louisiana. It has even received a name: Nemesis. One awkward fact of the Nemesis hypothesis is that there is no evidence whatever of a companion star of the Sun. It need not be very bright or very massive, a star much smaller and dimmer than the Sun would suffice, even a brown or a black dwarf (a planet-like body insufficiently massive to start "burning hydrogen" like a star). It is possible that this star already exists in one of the catalogues of dim stars without anyone having noted something peculiar, namely the enormous apparent motion of that star against the background of more distant stars (i.e. its parallax). If it should be found, few will doubt that it is the primary cause of periodic mass extinctions on Earth...However, since the examination of the entire sky in the far IR by IRAS with no "Nemesis" found, the existence of "Nemesis" is not very likely.

[Raup originally proposed the idea in a 1984 with University of Chicago colleague Dr. J. John Sepkoski]

[garbageseeker]

There are several theories to what causes the Oort Cloud. One is that the Solar System enters a molecular cloud or enters a very dense area of gravity in the Galaxy as it travels around the galactic center. My theory that a star passes close enough to disturb the Oort cloud leading to mass extinctions on earth. Carl Sagan in his book "Comet" outlines the theories.