Continental Drift and Plate Tectonics

Alfred Wegener 1880-1930 German scientist Introduced the Theory of Continental Drift in his book The Origin of the Continents and Oceans (1915) Many scientists had noticed the remarkable fit of the coastlines of South America & Africa First to use geological and paleontological evidence to show these continents were once joined

Evidence of Pangaea

Theory of Continental Drift Proposed by Wegener in 1915 Used evidence from climate, fossils and landforms to match up the continents All of the continents were once joined in one large supercontinent called Pangaea and have since drifted apart Wegener did not have a force to provide the movement so it was not accepted until the 1950’s Wegener spent much of his life defending his theory

Wegener’s Continental Drift http://www. ucmp. berkeley 225 million years ago all continents connected in one land mass called Pangaea 180-200 million years ago Pangaea separated into Laurasia and Gondwanaland

65 million years ago the continents move even further apart 135 million years ago Laurasia and Gondwanaland began to separate into continents 65 million years ago the continents move even further apart The position of the continents on Earth today

Untold Tragedies of Continental Drift

The Crust Continental Crust This is where we live! The Earth’s crust is made of: Continental Crust thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old - granite Oceanic Crust - thin (~7 km) - dense (sinks under continental crust) - Young - basalt The Earth has two different types of crust: Continental crust and Oceanic crust. Each has different properties and therefore behaves in different ways. Continental crust: Continental crust forms the land (the continents, as the name suggests) that we see today. Continental crust averages about 35 km thick. Under some mountain chains, crustal thickness is approximately twice that thickness (about 70 km thick). - The mountains we see on earth have deep roots in the crust that we can’t see. The crust “floats” on the more dense mantle and, like how only the tip of an iceberg sticks up out of the water, we see only the tip of the continental crust - the mountain ranges. Continental crust is less dense and therefore more buoyant than oceanic crust Continental crust contains some of the oldest rocks on Earth. - Ancient rocks exceeding 3.5 billion years in age are found on all of Earth's continents. The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) [Ga = billion years ago] and the Isua Supracrustal rocks in West Greenland (3.7 to 3.8 Ga), but well-studied rocks nearly as old are also found in the Minnesota River Valley in the USA (3.5-3.7 billion years), in Swaziland (3.4-3.5 billion years), and in Western Australia (3.4-3.6 billion years). Oceanic crust: As the name already suggests, this crust is below the oceans. Compared to continental crust, Oceanic crust is thin (6-11 km). It is more dense than continental crust and therefore when the two types of crust meet, oceanic crust will sink underneath continental crust. The rocks of the oceanic crust are very young compared with most of the rocks of the continental crust. They are not older than 200 million years.

Earth’s Interior Lithosphere: Area of the crust and the upper mantle. Outer most layer Continental crust (less dense granitic) Oceanic crust (more dense basaltic) Asthenosphere: Rocks are at or near melting point Exhibits plasticity – a solid that flows like a liquid

Assignment In your spiral – draw and color a picture of the Earth’s interior, labeling the following:

Wegener’s Puzzling Evidence 1. Label the land masses on each sheet. Color the fossil areas to match the legend below. 2. Cut out each of the continents along the edge of the continental shelf (the outermost dark line). Alfred Wegener's evidence for continental drift is shown on the cut-outs. Wegener used this evidence to reconstruct the positions of the continents relative to each other in the distant past. 3. Try to logically piece the continents together so that they form a giant supercontinent.

India Antarctica S. America Africa Australia

Plate Tectonics Proposed in 1960’s by a variety of scientists including Hess, Dietz and Vine Suggests that the lithosphere is broken up into many plates which are moving around the earth in different directions All of the continents were once together in one supercontinent – Pangaea Movement is caused by convection currents in the mantle of the Earth Explained the cause of earthquakes, volcanoes, mountain building

Plate Tectonics Plate Tectonics: Theory that the Earth’s lithosphere is broken into plates and float on the asthenosphere Convection Currents: Drives plate motion – hot magma rises from core, cools and sinks back to core – cycle starts over (think of a lava lamp)

Double Bubble Make a double bubble map of Continental Drift and Plate Tectonics

CONCLUSION Imagine you are Alfred Wegener in 1915. Write a Claim – Evidence – Reasoning about your theory of Continental Drift. Use the evidence from the lab we just completed. Your reasoning you can come up with on your own (Remember it is 1915 and you are Wegener)

CER Peer Editing Claim – All continents were once joined together and have since drifted apart = 20pts Is it a complete logical sentence = 10pts Evidence – Must mention at least 2 of the following: Dinosaur Fossils, Plant Fossils, Landforms (the way they fit together) = 30 pts Is it a complete sentence? = 10pts Reasoning – Does it make sense? = 20 pts Write the totals in the box at the bottom of the page