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In the late 1970s, geologist Walter
Alvarez discovered a layer of red
clay between fossil-containing limestone
deposits in Italy. His father, Nobel
laureate Luis Alvarez, suggested how
to analyze it. In 1980, neutron activation
analysis at Lawrence Berkeley National
Laboratory revealed that the clay
was rich in iridium, a metal that
is scarce in the Earth?s crust but
common in extraterrestrial objects.
Luis Alvarez then determined the global
extent of the iridium, its origin,
and the implications. The clay was
found at a geological boundary formed
65 million years ago, at a time of
mass extinction of many living species,
including the dinosaurs. Alvarez suggested
that the extinction was initiated
by the impact of an asteroid or giant
meteor, which caused a dust cloud
that blocked much of the sunlight,
leading to a drastic and devastating
global climate change. This hypothesis,
supported by a huge buried crater
where a meteorite may have struck
the Yucatán Peninsula of Mexico, is
considered by many scientists to be
the most likely explanation of the
dinosaur extinction.
Scientific Impact:
This work illustrated the value of
the study of isotopes (different forms
of the same element) as a tool to
better understand the environment;
the iridium anomaly has now been identified
at more than 75 sites worldwide. This
finding also led to development of
the controversial Nemesis theory,
which postulates that every 26 to
30 million years, a companion star
to the sun unleashes a storm of comets,
some of which strike the Earth.
Social Impact: The
public is fascinated by dinosaurs.
This hypothesis answers a long-standing
question of great interest to many
people, from scientists to schoolchildren.
Reference: "Extraterrestrial
cause for the Cretaceous-Tertiary
extinction," Science (1980).
URL:
http://www.lbl.gov/Science-Articles/Archive/dinosaur-extinction.html
Technical Contact:
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of High Energy and Nuclear
Physics |