Question

1. alfred wegener was the first scientist who proposed that continents may be moving. what evidence did he use to come to this conclusion?
2. according to wegeners theory, how was earth different 250 million years ago?
3. what are tectonic plates?
4. what causes the movement of plates?
5. what is the difference between the lithosphere and asthenosphere?
6. what are convection currents?
7. where do convection currents occur?
8. explain the difference between oceanic and continental lithosphere.

Explanation:

1. Alfred Wegener used evidence such as the fit of continents (like how South America and Africa seem to fit together), similar fossil distributions across continents (e.g., the same plant and animal fossils found on continents now separated by oceans), and matching rock formations and mountain ranges on different continents.
2. According to Wegener's theory (continental drift), 250 million years ago, Earth had a single super - continent called Pangaea.
3. Tectonic plates are large, rigid slabs of the Earth's lithosphere (the outer, solid part of the Earth) that move over the asthenosphere (a semi - molten layer beneath the lithosphere).
4. The movement of plates is mainly caused by convection currents in the asthenosphere. Hot, less - dense material rises, cools, and then sinks, creating a circular motion that exerts a force on the overlying tectonic plates.
5. The lithosphere is the rigid, outer layer of the Earth (including the crust and the upper, rigid part of the mantle), while the asthenosphere is a semi - molten, more ductile layer beneath the lithosphere.
6. Convection currents are circular movements of fluid (in the Earth's case, semi - molten rock in the asthenosphere) caused by differences in temperature and density. Hotter, less - dense material rises, and cooler, denser material sinks.
7. Convection currents occur in the asthenosphere (the semi - molten layer of the Earth's mantle).
8. Oceanic lithosphere is thinner (about 5 - 10 km thick), denser (composed mainly of basalt), and younger (constantly being created at mid - ocean ridges and destroyed at subduction zones). Continental lithosphere is thicker (about 30 - 70 km thick), less dense (composed mainly of granite), and older.

Answer:

1. Fit of continents, similar fossil distributions, and matching rock formations.
2. Had a single super - continent (Pangaea).
3. Large, rigid slabs of the Earth's lithosphere that move over the asthenosphere.
4. Convection currents in the asthenosphere.
5. Lithosphere is rigid (crust + upper rigid mantle); asthenosphere is semi - molten.
6. Circular movements of fluid (semi - molten rock in Earth) due to temperature/density differences.
7. In the asthenosphere.
8. Oceanic: thinner (5 - 10 km), denser (basalt), younger. Continental: thicker (30 - 70 km), less dense (granite), older.