Characteristics and Origins of the Solar System
In lecture 9, we discussed the possibility of an astronomical explanation for the extinction of the dinosaurs (the Cretaceous-Tertiary extinction event).††
The basis for this was the discovery of a world-wide layer of enhanced iridium at the K-T boundary.† An example of this is shown in the following site in Montana:
One can see the dark iridium-enhanced layer.†
The fact that iridium is enhanced in meteorites and asteroids suggested that a big impact produced the KT event.†
(1)† A search of the known impact craters on the Earth (see link from previous lecture)† led to the identification of the Chicxulub crater on the coast of Yucutan.
(2)† The huge size of this impactor would have created an unbelievably spectacular sight.† This has been represented in many artistís conceptions, such as that by Donald E. Davis below
(3)† There have been a total of five major extinction events in the history of Earth since the Cambrian period 550 million years ago,† with the Cretaceous-Tertiary event being the last one.† The location of these in geological history is shown in the attached link.
It is not known at the present if those other extinctions could also have been due to an asteroid impact.† It has been very recently suggested that the largest of the mass extinctions,† the end-Permian extinction,† was also due to an asteroid impact,† and that the impact site is off the northwest coast of† Australia.† However, this suggestion is very controversial,† and not accepted by many scientists in the field.† Time will tell.†