Geoscience Reference
In-Depth Information
F
IGURE
3
Luis and
Walter Alvarez studying the
K-T
section at Gubbio,
Italy. Walter Alvarez has his
finger on the boundary.
[Photo courtesy of
University of California
Lawrence Berkeley National
Laboratory.]
it have potential as a paperweight?), Luis Alvarez commented that
his son's description was one of the most fascinating revelations he
had ever heard. Walter explained that the limestones above and
below the layer contained about 5 percent clay, and suggested that
perhaps the limy portion had simply not been deposited for a time,
allowing the layer of pure clay to build up. Then, perhaps, lime
deposition had started again, leaving behind a thin layer of clay
sandwiched between two layers of limestone. Walter estimated that
this might have taken 5,000 years, which would mean that the
great K-T mass extinction had taken place in a mere instant of geo-
logic time. Luis immediately proposed that he and Walter measure
the length of time the clay layer had taken to form. Walter had suc-
ceeded in gaining his father's formidable attention and the game
was afoot.
IRIDIUM
The magnetic reversal time scale offered one possibility for deter-
mining how much time the clay layer represented: The particular
