Cretaceous-Tertiary boundary
(gcide) | Cretaceous-Tertiary boundary \Cre*ta"ceous-Tert"i*ar*y
boun"da*ry\ (kr[-e]*t[=a]"sh[u^]s), n.
a thin layer of geologic deposits, of varying thickness in
different parts of the world, found between the geological
strata identified as Cretaceous and the strata above,
identified as Tertiary; also, the time point or period
marking the boundary between the Cretaceous and Tertiary
periods.
Syn: K/T boundary.
[PJC]
Note: According to a theory gaining acceptance (as of 1997),
these deposits were formed as the debris of a large
comet or meteorite impact on the earth, which threw up
a large quantity of dust into the atmosphere, causing
profound though temporary climatic change, and caused
or hastened the extinction of numerous species,
including the dinosaurs. This hypothesis was first
postulated by Luis and Walter Alvarez on the basis of
an excess of iridium found in the boundary layer, and
was later supported by additional evidence of various
types. The impact is believed to have occurred at the
edge of the Yucatan peninsula in Mexico, forming what
is termed the [a
href="http:]/dsaing.uqac.uquebec.ca/~mhiggins/MIAC/chicxulub.htm">Chicxulub
crater, which is partly under the Gulf of Mexico, is
not evident from surface topography, and was detected
primarily by gravity anomaly readings and subsurface
geological characteristics.
[PJC] |