Unfinished Earth

1
Unfinished Earth

• History and modern continuation of planetary
  accretion

2
Impacts and Popular Culture

• Armegeddon
• Deep Impact
• Dinosaur Extinction 65 Ma

3
Earths Early History

• Hadean Eon Earths first 500 Ma
• Intense bombardment by bolides (meteors, comets,
  etc.)
• No permanent crust destroyed by impacts
• Little direct evidence on Earth
• Excellent evidence on Moon, Mars and other
  terrestrial planets

4
Craters on the Moon Hadean and later bombardment
5
Earth the water planet
6
Earth the water planet

• Presently, Oceans cover 71 of Earths surface
• Odds of impact on land are 29
• Water and oxygen weather rocks and destroy
  evidence of impacts

7
Crater Preservation

• Arid climate is more likely to preserve craters
  than humid climate
• Less weathering (chemical and physical breakdown)
  of rock and impact structure
• Less erosion removal of structure by running
  water and/or wind

Crater in Australian Outback
8
Craters in Quebec

• Greater age probably over 2 billion years old
• Much more humid climate
• Extensively eroded by glaciers in past 2 million
  years

9
Location of Craters on Earth
10
Craters in North America
11
Chicxulub 65 Ma Impact

• Timing is close to disappearance of dinosaurs and
  other creatures land sea
• Was this the cause?
• Other hypotheses
• Climate change
• Extensive volcanism
• Straw that broke the dinosaurs back?

12
Gene and Carolyn Shoemaker

• Gene Shoemaker, geologist
• Pioneer in study of impact structures worldwide
• Studied Meteor Crater, AZ
• Well-respected in geology, but not in astronomy
• Until Shoemaker-Levy 9!

13
Meteor Crater, Arizona

• Young impact structure
• Approximately 40,000 years old
• Arid climate excellent preservation
• Remnants of meteorite found in crater and in
  ejecta

14
Shoemaker-Levy 9
15
Significance of Shoemaker-Levy 9

• Convinced astronomers that such events were still
  possible
• Focused attention on near-Earth objects
• Showed how little we know of such objects
• Showed how completely unprepared we are
• Is anyone doing anything?

16
In-class Activity Jigsaw Presentations I

• Research assigned question You may work in teams
• It is permissible to trade questions within your
  group, but you are responsible for one question
• Prepare a 2-3 minute presentation on your
  question (visual aids may be helpful)
• Wednesday Questions 1-17
• Friday Questions 18-35
• Monday Questions 36-52