1. Continental Drift and Plate Tectonics

2. Continental Drift - An Idea Before Its Time
In 1858, Antonio Snider-Pellegrini, a French geographer and scientist, first hypothesized the possibility of continental drift.
In 1858, Snider-Pellegrini published his book, "The Creation and its Mysteries Unveiled“, in which he proposed that all of the continents were once connected together during the Pennsylvanian Period.
He based this theory on the fact that he had found plant fossils in both Europe and the United States that were identical.
He found matching fossils on all of the continents.

3. Continental Drift - An Idea Before Its Time
57 years later, German scientist Alfred Wegener proposed his continental drift hypothesis (1915.) His work was published as “The Origin of Continents and Oceans.” The continental drift hypothesis states that a supercontinent called Pangaea began breaking apart about 200 million years ago. The continents “drifted” to their present positions.

4. Pangaea approximately 200 million years ago
Figure 7.2

5. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
Wegener noted the obvious fit of South America and Africa.

6. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
He pointed out that fossils match across the seas.

7. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
He pointed out that fossils match across the seas.

8. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
He pointed out that fossils match across the seas.

9. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
Wegener also discovered that rock types and structures match across the seas.

10. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
There are similar mountain ranges on different continents.

11. Continental Drift - An Idea Before Its Time
Evidence Cited by Wegener
He noted that ancient climate evidence matches on the present-day continents.

12. Continental Drift - An Idea Before Its Time
The main objection to Wegener’s proposal was the inability to find a mechanism for continental drift.

13. The Launch Pad Tuesday, 1/31/17
List 5 pieces of evidence cited by Wegener that supported his hypothesis.
the fit of South America and Africa
fossils match across the seas
rock types and structures match across the seas
similar mountain ranges on different continents
similar ancient climates evidence matches on present-day continents

14. The Continental Drift Mechanism Discovered: Plate Tectonics
Plate tectonics is the theory that describes the large-scale motions of Earth's lithosphere. The model builds on the concepts of continental drift, developed by Wegener during the first decades of the 20th century. It was accepted by the geoscientific community after the concepts of seafloor spreading were developed in the late 1950s and early 1960s.

15. The Continental Drift Mechanism Discovered: Plate Tectonics
The concept of plate tectonics is more encompassing than the idea of continental drift. Plate tectonics is associated with Earth’s rigid outer shell, called the lithosphere. Earth’s lithosphere consists of several plates, which are moving very slowly across the mobile asthenosphere below. The largest of these plates is the Pacific plate. The plates are mostly beneath the ocean.

16. Figure 1.18 (left)

17. Figure 1.18 (right)

18. New crust is created at mid-oceanic ridges.
The Earth’s lithosphere is divided into plates, which move on top of the asthenosphere.

19. Plates move apart (diverge) and crash together (converge.)
Plate tectonics, the mechanism for continental drift, is caused by convection in the asthenosphere causing an upwelling through the lithosphere.

20. Plate Tectonics
The Earth’s asthenosphere lies just beneath the lithosphere. The asthenosphere is hotter and weaker than the lithosphere. This allows for the motion of the lithosphere over the asthenosphere

21. Describe the mechanism for continental drift.
The Launch Pad
Wednesday, 2/1/17
Describe the mechanism for continental drift.
The mechanism for continental drift is called “plate tectonics”, which states that the brittle lithosphere glides over the solid but mobile asthenosphere below.