GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
The Cretaceous-Tertiary Extinction II: One REALLY Bad Day!

The global nature of the K-T extinction would seem to favor some causal agent which could affect the whole planet. Cosmic (extraterrestrial) phenomena might be a good possibility.

1971: Suggestion by Dale Russell (dino paleontologist) and Wallace Tucker (astrophysicist): a supernova killed the dinosaurs.

Supernovae are exploding stars: put out TREMENDOUS amount of energy. If a star in a nearby solar system exploded, it would bombard surface of planet with radiation, bringing radiation sickness, cancer, etc.

Modern analogue: during 1950s through 1970s, greatest fear about nuclear war was radioactive fallout.


Fits prediction. However, problem because it is an untestable (and thus non- falsifiable) hypothesis:

So, remains as a potential but no reason should be supported. Was the leading candidate during the 1970s.

1980: Walter Alvarez was investigating a layer of clay in Gubbio, Italy at the K-T boundary. Wanted to determine length of time represented by the clay layer. Consulted dad (Nobel winning physicist Luis Alvarez) for possible solution. Suggestion:

The element used: iridium (a platinum-like metal, common in metallic asteroids but very rare in Earth's crust).

When examined Gubbio clay, found a huge increase in iridium (iridium spike) at base of clay: clearly not an “average” of infall.

Hypothesized: an asteroid impacted Earth at the K-T boundary

Modern analogue: fear of nuclear war during 1980s concerned with nuclear winter


Biotic prediction fits most of the predictions; search for geological signature was on.

Shocked Quartz:

Melt Glass (Tektites):

Tsunami (“tidal wave”) deposits:


So, great evidence for an impact at K-T independent of extinction.
Also, pattern consistent with proposed effects (although superacid rain, global fires, and global tsunami do not have good evidence and are probably “overkill” scenarios).

Question, though: was the extinction just from impact?

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Last modified: 14 July 2006