https://www.khanacademy.org/science/grade-7-science-tx/xe25057200abc6bd6:plate-tectonics/xe25057200abc6bd6:dynamic-earth/v/plate-tectonics-teks6 2026-06-30T14:20:41.927190319Z Plate tectonics In the 1800s, scientists began noticing that some continents fit together like the pieces of a jigsaw puzzle. This led to speculations that the continents were once connected, but moved apart. Evidence began supporting this new theory of "continental drift." For instance, fossils and rock formations on one continent matched those on another continent. Soon scientists discovered that new crust was being formed under the ocean. This idea of sea-floor spreading led to the modern theory of plate tectonics. The crust and upper part of the mantle compose the lithosphere, which is broken into massive, moving plates. The lithosphere rests on the asthenosphere, the upper part of the mantle. The rock of the asthenosphere is plastic, and moves the upper plates on convection currents of heat from Earth's interior. Mahesh Shenoy video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Plate tectonics In the 1800s, scientists began noticing that some continents fit together like the pieces of a jigsaw puzzle. This led to speculations that the continents were once connected, but moved apart. Evidence began supporting this new theory of "continental drift." For instance, fossils and rock formations on one continent matched those on another continent. Soon scientists discovered that new crust was being formed under the ocean. This idea of sea-floor spreading led to the modern theory of plate tectonics. The crust and upper part of the mantle compose the lithosphere, which is broken into massive, moving plates. The lithosphere rests on the asthenosphere, the upper part of the mantle. The rock of the asthenosphere is plastic, and moves the upper plates on convection currents of heat from Earth's interior. https://cdn.kastatic.org/ka-youtube-converted/u5uZWNOyoVY.mp4/u5uZWNOyoVY.mp4 614 Dynamic Earth https://www.khanacademy.org/science/grade-7-science-tx/xe25057200abc6bd6:plate-tectonics/xe25057200abc6bd6:dynamic-earth/e/understand-plate-tectonics-teks6 2026-06-30T14:20:41.927190319Z Understand: Plate tectonics Check your understanding of plate tectonics with this set of free, standards-aligned practice questions. Allen Ruch exercise