What is the best explanation for what happened

• What is the best explanation for what happened in this picture? • Were you there? • How do you know it happened? What evidence do you have? • How might this be applied to something like a murder?

Evidence A thing or things helpful in forming a conclusion or judgment: The broken window was evidence that a burglary had taken place. Scientists weigh the evidence for and against a hypothesis.

Cretaceous Calamity: How do we know what happened to the dinosaurs?

• The Dinosaurs took a giant dirt nap 65 million years ago and went extinct. • How do we know? • What evidence do we have and what story does it tell?

Evidence? • K-T boundary sedimentary band all over the world has iridium ranging from 20 -160 times normal amount. • Iridium is rare in Earth’s crust, but abundant in asteroids/comets Alvarez, L. W. Science. 1980, 208, 1095 -1108.

Iridium spike at K/T boundary • Iridium is an element that occurs in the Earths crust in only tiny proportions.

weak.

Soot particles found in boundary clay Similar to Fly Ash From Coal-Burning Plants Suggest global wildfires associated with ignition of large amounts of dead plant matter on Earth’s surface.

Richard D. Norris and the Ocean Drilling Project Leg 171 B Scientific Party http: //www. ussspiodp. org/Publications/ Greatest_Hits/contrib utors. html#n Photomicrographs by Brian Huber, Smithsonian Institution. Low-res. versions are hosted at: http: //www. ussspiodp. org/Education/r esources. html More information: http: //www. nmnh. si. e du/paleo/blast Sediment core from offshore South Carolina, showing the extinction across the K/T boundary. Core is 40 cm long (about 16 inches).

Tektites, glass beads found in boundary sediments Due to melting of rock by energy of bolide (asteroid or comet) impact ? Glass found in boundary sediments of Gulf of Mexico

Timothy Culler (UCB) et al. , Apollo 11 Crew, NASA http: //antwrp. gsfc. nasa. gov/apod/ap 000322. html • Cosmic spherule from the moon. • Spherules such as this are well-known from impact deposits, and are found in the special K/T impact bed that marks the end of the dinosaurs.

Shocked Quartz in K-T Boundary Clay Shock Metamorphism Has only been observed at meteorite impact sites and nuclear test sites

Chicxulub Crater • Impact site buried underneath Yucatán peninsula in Mexico, discovered by a geophysicist in the late 1970 s. • Took about 20 years to fully investigate crater • Evidence for impact: – Shocked quartz – Tektites – Gravity anomaly http: //en. wikipedia. org/wiki/Chicxulub_crater

Impact Site: Chicxulub Location of Chicxulub crater (180 -300 km in diameter) Image from geophyscal survey over Yucatan Peninsula Crater actually discovered in 1978 by a geophysicist working for Petróleos Mexicanos Pemex did not release the data for fear of revealing valuable information to competitors. “Rediscovered” by Alan Hildebrand in 1991

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Alvarez Impact • Able to calculate size of meteor – Would have to be 10 -15 km in diameter (size of a mountain, or Manhattan) • Impact of that size would have an incredible amount of energy – 1 x 108 megatons, 2 million times greater than most powerful thermonuclear bomb tested! Alvarez, L. W. Science. 1980, 208, 1095 -1108.

• “The initial impact crater was about 100 kilometers (60 miles) wide and 30 kilometers (18 miles) deep. ” • Fireball and airblast that engulfed the zone modeled by. T Earth Impact Effects Program

Global Firestorms Regional Tsunamis 32

NE Mexico: Tsunamites ? Believed to have been deposited by tsunami generated by impact Belize: Ejecta Blanket Poorly sorted debris believed to be ejecta deposited close to crater.

Computer model of effects of K-T Impact Winter No sunlight = no photosynthesis= cascade of death through food chains Earth in darkness for at least 6 months after asteroid impact

All non avian dinos =dead All large animals=dead

Fern Spike / Pollen Trough Pollen/spore ratio takes a dive at about same level as iridium spike Records early recolonization of land after impact winter ?

Asteroid and shock wave blast long trench Rings of complex crater form, by rebound Impact winter -debris injected into atmosphere -lots of dead, rotting organic matter -global wildfires -blocking of sunlight -consumption of ozone ?

So what happened to impactor ? Most of impactor probably vapourized during blast …but possible fragment 100 trillionth of a gram found in drillcore in NW Pacific