Tectonic Plates

Layers of Earth Lithosphere – outer part of the Earth’s crust. Composed of solid rock. Asthenosphere - the zone below the lithosphere which is more ‘plastic’ so it is easier to bend and move Radioactivity is the sourc of heat in the mantle

2 Kinds of Crust Continental – less dense, thicker Oceanic – more dense, thinner

2 Kinds of Mantle Upper – solid, floats on… Lower – plastic (somewhat fluid) Why? Earth’s crust and upper mantle “float” on the plastic portion of the mantle. (asthenosphere)

Convection Currents Movement of hot liquid or gas Heated – rises Cools – drops Earth’s Crust Cracks… Convection currents in mantle cause cracking in crust Thermal Convection cause seafloor to spread and continents to drift

Convergent Boundary Divergent Boundary

Divergent – Ocean to Ocean New crust formed and pushed up - Mid Oceanic Ridges Ex. Mid-Atlantic Ridge Ocean Ridges

Divergent- Continent to Continent Continent spreads, ocean basin may form Paleontologist noticed that fossils were on different continents Arthur Holmes – First proposed that thermal convection in the mantle causes continental drift Ex. Red Sea

Convergent – Ocean to Ocean Older slips below newer Subducted plate melts Volcanic islands formed Ex. Aleutian islands, Japan

Convergent – Ocean to Continent Ocean plate goes below continent Subduction Subducted plate partially melts Trenches – the deepest parts of the ocean. Volcanic mountains Ex. Western South America

Aleutian Islands Islands of Japan

Convergent – Continent to Continent Same densities, no subduction Compression, folding, uplifting Ex. Himalayas, Alps

Another type of plate movement… Transform faulting: Plates move past each other San Andreas Fault

How do you think scientists identified the plate boundaries? What is the “Ring of Fire?”

Crustal Plates “Connect the dots” – volcanoes and earthquakes 8 major plates

Pangea Theory 1912 – Alfred Wegener Idea that continents were once part of one large land mass – theory of continental drift How did he know? Continents’ shapes fit together like a puzzle Rocks and fossils found on different continents matched

Early 1960s Scientific evidence proves continental drift, plate tectonics, and Pangea theory

Ocean Features Picture 2