1. The Earth's Structure:
* Crust: The Earth's outermost layer, broken into large pieces called tectonic plates. There are two types:
* Continental crust: Thicker, less dense, made up of granite and other minerals.
* Oceanic crust: Thinner, denser, made up of basalt and gabbro.
* Mantle: A hot, semi-solid layer beneath the crust.
* Core: The Earth's center, made up of a solid inner core and a liquid outer core.
2. Plate Tectonics:
* Convection Currents: Heat from the Earth's core creates convection currents within the mantle. These currents move the tectonic plates above.
* Plate Movement: Plates constantly move in different directions, colliding, separating, or sliding past each other. These movements are responsible for earthquakes, volcanic eruptions, mountain building, and the formation of continents and oceans.
3. Plate Boundaries:
* Convergent Boundaries: Where plates collide.
* Oceanic-Oceanic: One plate subducts (sinks) under the other, forming trenches and volcanic island arcs.
* Oceanic-Continental: Oceanic plate subducts under continental plate, causing volcanoes and mountain ranges.
* Continental-Continental: Plates collide and buckle upwards, creating mountain ranges.
* Divergent Boundaries: Where plates move apart.
* Oceanic-Oceanic: Magma rises from the mantle, creating new oceanic crust and mid-ocean ridges.
* Continental-Continental: Continents split apart, forming rift valleys and eventually new oceans.
* Transform Boundaries: Where plates slide past each other. This causes earthquakes.
4. Evidence of Plate Fit:
* Continental Shapes: The continents fit together like puzzle pieces, particularly South America and Africa.
* Fossil Evidence: Identical fossils found on different continents, suggesting they were once connected.
* Rock Types and Structures: Similar rock types and geologic structures found on different continents.
* Magnetic Anomalies: Patterns of magnetic striping on the ocean floor provide evidence of seafloor spreading and plate movement.
The Big Picture:
Tectonic plates are constantly in motion, shaping the Earth's surface over millions of years. While they don't fit together perfectly today, they once did, forming a supercontinent called Pangaea. This understanding of plate tectonics is a revolutionary theory that helps us understand the Earth's dynamic nature.
