GEOLOGY

1. GEOLOGY Chapter 10 Plate Tectonics 10.3 The Changing Continents

2. 10.3 The Changing Continents Objectives • Identify how movements of tectonic plates change Earth’s surface. • Summarize how movements of tectonic plates have influenced climates and life on Earth. • Describe the supercontinent cycle.

3. Reshaping Earth’s Crust • Cratons are large areas of stable rock older than 540 million years that exist on all continents today. • Cratons that have been exposed at the Earth’s surface are called shields. • Cratons are the cores around which the modern continents are formed. • Rifting is the process by which Earth’s crust breaks apart and it can occur within continental crust or oceanic crust.

4. Reshaping Earth’s Crust • Continental crust is thicker than oceanic crust and has a high silica content – making continental crust act as an insulator. • Heat from the mantle builds up under the continent causing the lithosphere to become thinner and weaken. • Eventually a zone of weakness breaks forming a rift.

6. Reshaping Earth’s Crust • Continents can change shape by breaking apart and gaining material. • A terrane is a section of geologic lithosphere that has a unique geologic history that is different from that of the surrounding lithosphere. • Three characteristics can be used to identify terranes. • Contains rocks and fossils that differ from those of surrounding terranes • Major faults at the boundaries of a terrane • Magnetic properties of a terrane are generally different from those surrounding it

7. Reshaping Earth’s Crust • Terranes become part of a continent at convergent boundaries. • Accretion is the process in which a terrane becomes part of another continent. • When a terrane is scraped off of a subducting plate, it may form mountains or just add to the surface area of the continent. • Terranes can be small volcanic islands, atolls, sea mounts, large chunks of continent.

8. Reshaping Earth’s Crust • Large mountain chains form when large terranes collide, such as the Himalaya Mountains – when India began colliding with Asia about 45 million years ago.

9. Effects of Continental Change • The past movements of tectonic plates have an impact on modern climate. • Latitude and longitude (both determined by continental movement) of a continent have an effect on climate as well as ocean currents and proximity to other landmasses. • Mountain ranges affect airflow and wind patterns as well as whether or not moisture makes it from one region to another. • Shifts in ocean currents and air and moisture flow have a major impact on climate change.

10. Effects of Continental Change • Most landmasses on Earth have been covered by glaciers at some time in the past. • At one point, a global ice sheet formed when the continents were amassed near the South Pole.

11. Effects of Continental Change • Populations of organisms are formed as mountain chains are uplifted and rift valleys form. • New species may evolve when an existing species is separated into different populations. • Isolation may also protect populations from predators or competitors.

12. The Supercontinent Cycle • The supercontinent cycle is the process by which supercontinents form and break apart over millions of years. • As continents move about through the process of plate tectonics, they converge every so often creating a cycle. • The movement of continental plates toward convergent boundaries cause inevitable collisions. • Over time the continents collide to form a giant supercontinent.

13. The Supercontinent Cycle • Since continental crust does not subduct (it buckles up to form large mountain chains), convergent boundaries where continents collide often become geologically inactive and spreading centers must form elsewhere. • This creates rifts elsewhere in the supercontinent. • Pangaea is the supercontinent that formed about 300 million years ago and began to break up about 250 million years ago.

14. The Supercontinent Cycle • The Appalachian Mountains of North America and the Ural Mountains of Russia formed during the collisions of continents during the formation of Pangaea. • The Tethys Sea cut into the eastern edge of the supercontinent. • The large, global ocean that surrounded the rest of Pangaea was Panthalassa. • Pangaea broke up into two continents, Laurasia and Gondwanaland about 250 million years ago.

15. The Supercontinent Cycle • The large east-west rift that split Pangaea sent Laurasia drifting and spinning slowly northward. • Another rift (eventually becoming the North Atlantic Ocean) then separated Laurasia into North America and Eurasia. • The Tethys Sea closed during the rotation of Laurasia and eventually became the Mediterranean. • About 150 million years ago, a rift (eventually becoming the South Atlantic Ocean) developed between Africa and South America.

16. The Supercontinent Cycle • Australia, India, and Antarctica then broke apart and drifted away. • India would later collide with Eurasia (Asia) to form the Himalaya Mountains. • Slowly, since the breakup of Pangaea, the continents have drifted to their current positions, sometimes picking up terranes along the way. • With the knowledge of current tectonic movement and past patterns, we can predict what the next supercontinent will look like.

37. References • Rift Formation - http://www-geol.unine.ch/Petrology/Research/theme1.html • India/Asia Convergence - http://www-class.unl.edu/geol101i/15c_glaciers.htm • Late Permian South Pole View - http://www3.interscience.wiley.com:8100/legacy/college/levin/0470000201/chap_tutorial/ch09/chapter09-5.html • Paleomaps of Continental Movement - http://scotese.com/late.htm