Plate Tectonics Theory: Putting It All Together
The plate tectonics theory combines continental drift and seafloor spreading into one unified explanation. Earth's lithosphere is broken into major plates that float on the asthenosphere like puzzle pieces on a slow-moving conveyor belt.
Seven major plates make up 94% of Earth's surface: North American, South American, Pacific, Eurasian, Australian-Indian, Antarctic, and African plates. Several intermediate-sized plates like the Philippine, Caribbean, and Nazca plates fill in the gaps.
Multiple lines of evidence support this theory: ocean drilling by the Glomar Challenger showed that seafloor rocks get progressively older away from ridges, paleomagnetism revealed magnetic stripe patterns, and the distribution of volcanoes and earthquakes perfectly matches plate boundaries. Paleontological evidence from fossils and glaciation evidence from ancient ice sheets all confirm that continents have indeed moved over geological time.
The Big Picture: Plate tectonics explains almost everything - why we have earthquakes, volcanoes, mountains, and even why similar fossils appear on different continents. It's the unifying theory that ties Earth science together!