8 th Grade Science

1. 8th Grade Science Unit 8: Changes Over Time Lesson 1: Natural Events Contribute to Extinction Vocabulary of Instruction

2. Mass extinction is the process in which a huge numbers of species die out suddenly. The dinosaurs (and many other species) became extinct, probably because of an asteroid that hit the Earth. Theory For Mass Extinctions 1. Mass Extinction

3. 1-B. Mass Extinction Theory • This close-up recreation shows the fireball descending, a large tidal wave rising off the Yucatan coast, the coastal region being inundated by the ocean, and the emergence of the impact crater.

4. Mass Extinction in the Yucatan Peninsula

5. 1-C. Mass Extinction Theory • Although most dinosaurs were probably killed off in the initial event where returning impact debris superheated the upper atmosphere, the after events would have been very destructive too.

6. 1-D. Mass Extinction Theory • There would have been huge tidal waves from the shock, and possibly the impact triggered large earthquakes that caused even more extinctions. • Afterwards, the upper atmosphere would have been saturated with gases from the massive fires, resulting in years of climate change that included severe acid rain.

7. Mass Extinction Theory

8. Mass Extinction Theory

9. 1-E. Mass Extinction • Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction rate. • The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others as it marks the extinction of nearly all dinosaur species, which were the dominant animal class of the period. • In the past 540 million years there have been five major events when over 50% of animal species died. • There probably were mass extinctions in the Archean and ProterozoicEons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record.

10. Mass Extinction Theory

11. 1-F. Mass Extinction • Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. • These differences stem from the threshold chosen for describing an extinction event as "major", and the data chosen to measure past biodiversity.

12. 1-G. Mass Extinction Theory Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms.

13. Catastrophic events are sudden, natural or man-made situations where change and destruction may occur without prior knowledge or preparation.  Such occurrences may limit normal functions in daily living including communications and travel. Catastrophic Events include the following: Impact Events Volcanic Eruptions Tsunamis Methane Hydrate Eruptions 2. Catastrophic Events

14. Man Made Catastrophic Events

15. * Coming up on the right, you can see the Meteor Crater, which is a major tourist attraction in northern Arizona. * It was formed when a lump of nickel and iron, roughly 150 feet in diameter and weighing 300,000 tons, struck the earth at about 40,000 miles an hour, scattering white-hot debris for miles in every direction. * The hole measures nearly one mile across and is 570 feet deep. 2-A. Catastrophic Events

16. 2-B. Catastrophic Events Impact Crater Sites around the World

17. 2-C. Catastrophic Events • The tendency to discount impact processes as a factor in the Earth's more recent geologic history was severely challenged by the interpretation in 1980 that Cretaceous-Tertiary (K-T) boundary sediments world-wide were due to a major impact event and that impact was the causal agent for a mass extinction event. Impact Crater Sites in North America

18. The Day the Sands Caught Fire A desert impact site demonstrates the wrath of rocks from space