1. What Killed the Dinosaurs?

2. K/T Extinction Boundary
65 million years ago, earth experienced a global mass extinction event: dinosaurs disappeared
that extinction defines the boundary between the Cretaceous and Tertiary (abbreviated K and T) geological periods and, a broader scale, the boundary between the Mesozoic and Cenozoic eras.

3. The cause of the K-T extinctions is one of the great mysteries in science, and scientists have proposed many kinds of theories to account for it. They range from asteroid or comet impacts, volcanism, sea level changes, supernova explosions, and on and on.

4. What Is a Mass Extinction?
an episode in evolutionary history where more than 50% of all known species living at that time went extinct in a short period of time (less than 2 million years or so).

5. Permian-Triassic extinction
Life on Earth nearly was wiped out -- an estimated 90% of all species living at that time were extinguished.
Trilobites were the dominant marine organism; wiped out.

6. CSI: Dinosaur Demise The Fossil Record - It's not perfect, gaps
Time Resolution: gets worse with increasing age; gradual decline of dinosaurs vs. a sudden cataclysm is almost intractable
Falsifiability - Sad but true: many “hypotheses” about dinosaur extinction sound quite convincing and might even be correct, but, as you know, are not really science if they cannot be tested and falsified if untrue.

7. Wrong Hypotheses That Have Been Tested
Dinosaurs got so darned big that they crushed themselves
Mammals outcompeted the dinosaurs
Mammals ate all of the dinosaurs eggs
Cosmic rays killed the dinosaurs

8. Common Ground
There was global climatic change; the environment changed from a warm, mild one in the Mesozoic to a cooler, more varied one in the Cenozoic
Many organisms; both marine and terrestrial, vertebrate and invertebrate; went extinct
At or near the K/T boundary, there was iridium, shocked quartz, tektites, and a soot layer was found in many areas (evidence for widespread forest fires), all consistent with a catastrophic event

9. Iridium spike at K/T boundary
Iridium is an element that occurs in the Earths crust in only tiny proportions, but is much more common in chondrite meteorites.
Deep volcanoes also a source

10. Shocked Quartz
High pressures cause what is known as shock metamorphism, this deforms the structure of the quartz and creates parallel laminar ripples.
It is found all over the world, not just locally.
No other process on the planet creates this type of quartz.
Meteors; volcanoes?

11. TEKTITES Tektites are naturally occurring silica glass
formed during the impact of a meteor.
Also formed from volcanic eruptions

12. Cosmic Catastrophes
Tektites are formed when molten material is injected into the atmosphere and cools before touching the ground
Volcanoes, meteors are a source

13. Dinosaurs on Fire
There is a large soot layer associated with the K/T boundary.
This layer is consistent with catastrophic fires that may have swept the surface of the earth at this time.
Such a fire would have killed most large terrestrial animals.

14. Nuclear Winter
Lingering airborne debris is believed to have triggered darkness and a decline in the global temperature

15. Extrinsic Catastrophists: CSI Asteroids

16. Extrinsic Catastrophists
This side of the controversy holds that the ultimate cause of the K-T extinction was extrinsic, meaning of an extraterrestrial nature, and catastrophic, meaning fairly sudden and punctuated. The main hypothesis was proposed in 1980 by (among others) Luis and Walter Alvarez, geologists at the University of California at Berkeley.

17. The Alvarez Hypothesis
A large extraterrestrial object collided with the Earth, its impact throwing up enough dust to cause the climatic change.
The iridium layer is what prompted the Alvarez team to blame an asteroid impact for the extinction -- asteroids and similar extraterrestrial bodies are higher in iridium content than the Earth's crust, so they figured that the iridium layer must be composed of the dust from the vaporized meteor.
No crater was found, but it was assumed that one existed that was about 65 million years old and 100 kilometers (about 65 miles) in diameter.

18. Where Is the Smoking Gun?

19. Subducted? Evidence removed!

20. CHICXULUB CRATER
Survey work related to oil exploration in 1981 first identified concentric rings of gravitational anomalies around the northwest coast of Yucatan.
Hildebrand (1991) located two concentric rings which suggested an outer rim of 180 km.

21. The Smoking Gun!
Some 65 million years ago, a 10 to 12 km in size asteroid or comet crashed on the Yucatan platform and formed the > 200 km in diameter Chicxulub crater.
If a 10km diameter object impacted at the point at which it struck it would have a velocity of roughly 100,000 km/h.

22. Magnitude of Impact
The K/T impact, as it is now referred to, resulted in 100 million megatons of energy.
Equivalent to the energy of 300 million nuclear weapons

23. Impact Forces
Computer model of the Chicxulub impact showing the raising fireball and CO2 plumes and ejecta curtain material (from Alvarez, Claeys and Kieffer, Science 1995)

24. CONCLUSIONS
There has been no settlement to the issue so far, and no clear one is foreseeable. Both sides claim to hold the majority of proponents in science; it seems that (greatly over- generalizing) many paleontologists lean towards the intrinsic side, while many astronomers and physicists favor the extrinsic side, and geologists are probably evenly split between the two.