The Earth’s Drifting Continents

Theory of Continental Drift Alfred Wegener suggested that the continents were once together and have since drifted apart. Was not accepted until 30 years later.

Pangea The earth had a single landmass that broke up into large pieces, which have since moved apart.

Evidence to Support Continental Drift Fossils- preserved remains of organisms Rock formations and deposits; coal, limestone, salt, etc.

Basalt from a volcanic eruption.                    Basalt from a volcanic eruption.

Evidence Cont… Mountain chains Coal fields Glacial deposits

The Earth’s Spreading Ocean Floor

Mid-ocean Ridges Under water mountains and valleys.

Trenches V shaped valleys at the bottom of oceans, which are usually found on the edges of continents and islands. Deepest part of the ocean

                                                                                          

Ocean Floor Spreading Lava erupts at rift valleys and hardens to form new ocean floor. Explains how the continents move.

Subduction Process in which old crust plunges back into the earth. Rocks are pushed deep into trenches where they are melted by the heat of the earth. They recycle.

Evidence to Support Ocean Floor Spreading Rock age- youngest rocks are found near rift valleys and oldest rocks are found near trenches.

Evidence Cont… Magnetic Stripes- magnetic rock line up with the poles equally on both sides of the mid-ocean ridge.