Plate Tectonics

4. ridge- an underwater mountain range that stretches along the center of much of Earth's ocean floor that forms when two oceanic plates diverge
5. spreading- hot, less dense material below Earth's crust rises toward the surface at the mid-ocean ridges, flows sideways, carrying the seafloor away from the ridge in both directions leaving the youngest rocks at/near the ridge and the oldest farther away
10. – all of the crust and the upper solid portion of the mantle
11. – boundary that forms when two plates slide past each other; causes earthquakes
12. – the plastic-like layer of the mantle located below the lithosphere
15. Wegener- German scientist who proposed the hypothesis of continental drift; his ideas were initially rejected
17. – reptile fossil found in South America and Africa
18. – fossil plant found in Africa, Australia, India, South America, and Antarctica
19. – boundary that forms when two plates collide; causes subduction, trenches, mountains, volcanoes
21. a sensing device used to detect magnetic fields on the rocks on the ocean floor

1. Drift – Wegener’s hypothesis that continents have slowly moved to their present-day locations.
2. – boundary that forms when two plates move apart; causes mid-ocean ridges, rift zones, earthquakes
3. Hess- proposed the theory of seafloor spreading in the 1960s
6. mountains- mountains similar to those in Greenland and Europe
7. tectonics – the theory that Earth’s crust and part of the upper mantle are broken into sections called plates that move on a plastic-like layer of the mantle (asthenosphere)
8. – sections of Earth’s crust and upper part of the mantle (the lithosphere)
9. current – the cycle of heating, rising, cooling, and sinking that occurs in the mantle that is the driving force of plate tectonics
13. valley - a valley that forms when two plates diverge
14. – the process by which the ocean floor sinks into the mantle where the crust is melted and recycled
16. ocean trench – feature formed where subduction occurs; island arcs and volcanic arcs can be created
20. when Earth's magnetic force runs the opposite way. Recorded in the rocks along the mid-ocean ridge. Occurs over thousands or millions of years