1. Bell Questions 9/14/11 1.What do scientists believe the Earth was formed from? 2.How old have scientists calculated the earth to be? 3.List three things the earth and the moon have in common.

3. Wegener’s Hypothesis Continental drift the continents once formed a single landmass, broke up, and drifted to their present location Proposed by Alfred Wegener in 1912

4. Wegener’s Evidence Fossil Evidence: fossils of the same plants and animals could be found in areas of continents that had once been connected. Evidence from Rock Formations: ages and types of rocks on different coasts matched. Climatic Evidence: changes in climatic patterns. Places that are now tropical show evidence of glaciers.

6. Bell Questions 9/15/11 1.How are most mountain chains like the Alps formed? 2.What freed life forms from the ocean? 3.What kind of rock made up the first landmass?

7. Wegener’s Missing Mechanisms Wegener proposed that the continents moved by plowing through the rock of the ocean floor. Disproved by geologic evidence.

8. Mid-ocean ridge Mid-ocean ridge - a long, undersea mountain chain that has a steep, narrow valley at its center.

9. Mid-ocean ridge

10. Discoveries about the Mid-ocean ridge 1.The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge 2.The ocean floor is very young. 175 million years old compared to rocks on land 3.8 billion years old. 3.Rocks closer to a mid-ocean ridge are younger than rocks farther from the ridge.

11. Mid-ocean ridge

12. Sea-Floor Spreading Sea-floor spreading the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth’s surface

13. Sea-Floor Spreading As the ocean floor spreads apart, magma rises to fill the rift and then cools to form new rock.

14. Sea-Floor Spreading

16. Paleomagnetism Paleomagnetism the study of the magnetic properties in rock, specifically the alignment of magnetic minerals as it relates to the reversal of Earth’s magnetic poles.

17. Magnetic Reversals Earth’s magnetic poles don’t stay in the same place. Rocks with magnetic fields that point north (normal polarity) Rocks with magnetic fields that point south (reversed polarity)

18. Paleomagnetism Magnetic Symmetry The pattern of magnetic symmetry indicates that new rock forms at the center of a ridge and then moves away from the center in opposite directions.

19. Wegener Redeemed Sea-floor spreading was the mechanism that verified Wegener’s hypothesis of continental drift.