Did an impact cause the Did an impact cause the demise of the dinosaurs?demise of the dinosaurs?

This weekThis 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 BoundaryThe 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 hypothesis1980 hypothesis

• Luis Alvarez, his son Walter, and their collaborators propose that a circa 10km asteroid hit the earth then

They further proposedThey 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 impactEvidence 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 CraterChicxulub Crater

Gravity map of Chicxulub areaGravity map of Chicxulub area

ChicxulubChicxulub

• 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!)

ChicxulubChicxulub

• 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 TrapsDeccan Traps

• Large basalt eruptions about 65 million years ago

• Major eruptions lasted for several million years

Deccan trapsDeccan 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?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 What about other mass extinctions?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 K-T event