Transcript Impacts and Mass Extinctions

Did an impact cause the
demise of the dinosaurs?
This week
• Tuesday night: Observing if clear, roof of BPS
• Wednesday night: If Tuesday is cloudy, how many of you
could observe Wednesday night?
• Thursday night: public lecture 7:30pm (but costs $5) at
Abrams Planetarium by Megan Donahue: The Secret
Universe: Astronomical Espionage with the Spitzer
Space Telescope
• Friday and Saturday: Public open house nights at the
campus observatory (if clear), 9-11pm
The Cretaceous/Tertiary Boundary
• In the 65 million year
old layer marking the
end of the Cretaceous
era is an
overabundance of the
element iridium
1980 hypothesis
• Luis Alvarez, his son
Walter, and their
collaborators propose
that a circa 10km
asteroid hit the earth
then
They further proposed
• That the consequences of
the impact were
responsible for the mass
extinction at the end of
the cretaceous
– About 85% of all species
become extinct
– But some species survive –
birds, mammals, turtles,
snakes among them
Evidence in favor of an impact
• Shocked quartz and stishovite found in the iridium layer suggest the
conditions of heat and pressure found in an impact
• Glass beads – melted ejecta?
• Evidence of giant tsunami in Caribbean area
• Evidence of excess of isotopically uniform carbon (large-scale fires)
Chicxulub Crater
Gravity map of Chicxulub area
Chicxulub
• An impact from about a 10 km
object would be needed to
create this crater
• Such impacts are expected
about every 100 million years
or so (note that during the time
of heavy bombardment in the
early solar system such
impacts might have come as
frequently as once a month!)
Chicxulub
• The effects of the impact are still debated
– A “meteor winter” may have been one of the consequences
– Others suggest release carbon dioxide could raise temperatures
– There may have been atmospheric changes from the sulfur
containing rocks at the impact site
– Direct damage would of course be widespread in the vicinity
– Some have suggested that other impacts at about the same time
may have contributed to the effects of the Chicxulub impact
•
http://www.ucmp.berkeley.edu/education/events/cowen2b.html
Deccan Traps
• Large basalt eruptions
about 65 million years
ago
• Major eruptions lasted for
several million years
Deccan traps
• Volcanoes can yield iridium rich material,
however the layer of iridium enrichment is
narrower than the timescale of the Deccan
eruptions, consistent with an
extraterrestrial origin
How sudden were the extinctions?
• Unfortunately, published
results are not in full accord
• From a remove of 65 million
years, it is hard to tell whether
the “sudden” disappearance of
a fossil took place over 1 year
or 500,000 years
• Nor is it easy to determine
when the extinctions and the
formation of the Chicxulub
crater were exactly coincident
• Big fights among holders of
different theories
What about other mass
extinctions?
•
•
At least 5 major mass extinctions
seem to have occurred
At the end of the Permian period,
about 245 million years ago there
was a major extinction event
– One of the largest extinction
events ever, with 95% of sea life
and 70% of land families going
extinct
– Some have claimed evidence for
a large impact at this time, but
others dispute this
– The evidence for an impact is
more controversial than for the KT event