Lesson 7 in Earth and Life science Continental Drift

Continental Drift is the theory that Earth's continents have moved over geological time and were once joined together in a single supercontinent called Pangaea. Proposed by Alfred Wegener in 1912, the theory suggests that the continents slowly drift across the Earth's surface due to movements in the Earth's mantle.

1. Objective 1. Describe the continental drift theory 2. Discuss evidence that support continental

2. CONTINENTAL DRIFT

3. Continental drift is a theory proposed by Alfred Wegener in the early 20th century. He suggested that the continents were once part of a supercontinent called Pangaea and have since moved apart to their current positions.

4. According to this theory, the continents "drift" on the Earth's surface over millions of years due to the movement of the Earth's crust.

5. Wegener's theory met with skepticism during his time because he couldn't provide a satisfactory mechanism for how continents could move.

6. Plate tectonics The Earth’s CRUST is made of many slabs, or pieces of rock. these pieces of rocks are called TECTONIC PLATES. The plates slide around on a layer of hot, slightly melted rock called Earth’s MANTLE .

7. The plates move very slowly, just a few inches per year . In some places the plates move apart . In other places the plates crunch together . In still other places, the plates slide past each other .

8. PLATES CAN MOVE APART The plates that make up the bottom of the Atlantic Ocean are slowly moving apart. As they move apart, they leave a gap in the ocean floor. Hot rock called magma oozes up through the gap. The magma cools and hardens into rock.

9. The new rock makes new crust. Every year, the bottom of the Atlantic Ocean spreads about 1 inch (2.5 centimeters). As a result, Europe and North America become a tiny bit farther apart.

10. The new crust can pile up to make underwater mountains. A range of mountains formed underwater in the middle of the Atlantic Ocean. These mountains are called the Mid-Atlantic Ridge.

11. Plates moving apart on land or under the sea can also make valleys. This happens when new rock does not completely fill up the space created as plates move apart. The valleys are called rift valleys. There is a long rift valley on land in Africa.

12. PLATES CAN BUMP INTO EACH OTHER Sometimes plates crumple up when they hit each other. The edges go up in the air. When two gigantic plates hit each other, they make mountains. The Himalayas in Asia and the Andes in South America are mountains that were made by plates crashing together .

13. HIMALAYAS (ASIA)

14. ANDES ( SOUTH AMERICA)

15. PLATES CAN SLIDE PAST EACH OTHER Plates that slide past each other make breaks in the crust called faults. The edges of sliding plates can get stuck together.

16. The plates keep trying to move, and pressure builds up. Suddenly, the plates break free. Plates that move suddenly can cause an earthquake .

17. HOW DO WE KNOW THE PLATES MOVE? - Scientists see new crust being made between plates under the Atlantic Ocean. - They also know that in the distant past the same types of animals lived on continents that are now far apart. -They can see on a globe that the shapes of these continents fit together like pieces of a puzzle.