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Evidence for Plate Tectonics
Evidence for Plate Tectonics
The theory of plate tectonics explains how Earth’s outer shell, called the lithosphere, is broken into large pieces called plates that move slowly over the softer mantle beneath them. But how do scientists know this is true? Over the last century, several key pieces of evidence have confirmed the theory:
- Fit of the Continents
South America and Africa look like they could fit together like puzzle pieces. This suggested they were once joined in a supercontinent (Pangaea) and later drifted apart.
2. Fossil Evidence
2. Fossil Evidence
Identical fossils of plants and animals, such as Mesosaurus (a freshwater reptile), are found on continents now separated by oceans. This shows the continents were once connected.
3. Seafloor Spreading
3. Seafloor Spreading
At mid-ocean ridges, new oceanic crust forms as magma rises and hardens. Rocks farther from the ridges are older, proving the seafloor is spreading apart.
4. Age of the Seafloor
4. Age of the Seafloor
At mid-ocean ridges, magma rises, cools, and forms new crust. The youngest rocks are found right at the ridge, while rocks get progressively older the farther away you go. This pattern matches the idea of seafloor spreading, where new crust is created and then pushed outward by moving plates.
5. Depth of Ocean Sediments
5. Depth of Ocean Sediments
Near the ridges, the seafloor is young, so only a thin layer of sediments has had time to build up. Farther from the ridge, the crust is older, so there is a thicker layer of sediments that has accumulated over millions of years. This increasing sediment depth with distance from the ridge is exactly what scientists expect if the seafloor is spreading.
6. Locations of Earthquakes and Volcanoes
6. Locations of Earthquakes and Volcanoes
Earthquakes and Volcanoes are almost exclusively located at plate boundaries. Another strong piece of evidence for plate tectonics.
Together, these lines of evidence show that Earth’s plates are constantly moving, reshaping continents and oceans, building mountains, and causing earthquakes and volcanic eruptions.
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