Evidence for Movement of Continents

Biggest obstacles to acceptance

• You can not see the continent move

• You can not feel the motion of the continent

• Yet a lot of physical evidence supports the idea that the continents move across the earth over time

Goal for this section

• Review the evidence that supports continental drift

• Understand the process that allows continents to move (theory of plate tectonics)

• Predict what happens to continents and the life on them as they move

Question

• What kind of physical evidence could be used to show that continents move?

Alfred Wegener

Alfred Wegener

• First proposed that continents move over time (continental drift) in early 20th century

• Meteorologist and German (what effect on acceptance of his ideas did his background have)

• Could not explain how continents move, led to rejection of theory

Evidence for continental drift

1) Physical shape of continents

2) Rock evidence of change in climate

3) Fossil evidence, including Mesosaurus

4) Location of volcanoes and earthquakes

5) Difference in ages of oceanic crust vs continental crust. Relate age to plate boundaries

6) Magnetic orientation of rock on either side of the Mid Atlantic ridge

Shape of the continents

Pangaea and Panthalassa

Pangea or Pangaea

• Pangaea- name of supercontinent the last time the continents were joined

• Panthalassa- name of the single ocean that existed at the same time as Pangaea

Evidence for movement of continents

Fossil evidence

• Different animals and plants require certain climate conditions to live

• When the fossils found do not match current climate…

• How did the climate change so much?

Fossils of ferns found in Antarctica

Mesosauras

• Small aquatic reptile• Less than 3 ft long• Breathed air• Freshwater hunter• Fossils found only in

eastern South America and western Africa

The mystery

• In the 1800s, scientists began finding fossils of these ancient reptiles, which had long since become extinct. These fossils were found in only two regions, southern Africa and the southern part of South America. The shaded areas on the map show where fossils of Mesosaurus have been discovered. This distribution is a curious one—only two regions far from each other and separated by the Atlantic Ocean.

• What could explain this distribution?

From experience with modern plants and land animal

• Migrate and expand primarily over land, not oceans.

How can the exact same land animal or plant species have existed on a number of unconnected continents ?

Possible answers

• Either the animals evolved the same all over the world (not consistent with recent evolution)

• Or

• The places were connected and closer in the past

Paper Exercise

Use the fossil evidence of shown to reassemble a supercontinent made from South America, Africa, Antarctica, India and Austraila

1. Remember, all regions of the same fossil must connect

2. It is ok to slightly overlap continents3. Glue final answer in your comp book

point of exercise

Areas where fossils of land animals/plants located must be connected

This is possible only if Continents can move

Microfossils

• Very small life forms, organic matter

• Diatoms in ocean• Algae, pollen on land

• Localized• Quick evolution

Rock evidence

Rock Type indicate climate

Change in climate suggest requires change

Coal

• Made from organic remains of vast jungle swamps

• Indicates a tropical environment

Gypsum

• Created from what remains after ocean water has completely evaporated

• Indicates a hot, dry environment

Rock Evidence for glaciers

• Deposits made up of rocks with different size, composition, and roughness

Evidence of Glaciers

• Striations

Location of volcanoes and earthquakes around the world

World Volcanoes

World Earthquakes

Volcanoes (triangles) Earthquakes (circles)

Location of volcanoes and Earthquakes

• Volcanoes and earthquake line up, not randomly placed around the world

• Something must be happening on a global scale to account for this match

Difference in the maximum ages of ocean and continental rocks

• Max Oceanic Rock: 180 million Years old

• Max Continental Rock: over 4 Billion years old

• If continents did not move, both types should have similar ages

Age of the sea floor

• Red = young• Blue = old

• Connect lines created by earthquakes to ages

• Oldest Oceanic crust is farthest away from the ocean ridges

• Newest Oceanic rock is found at the oceanic ridges

Location of world’s Oldest rocks

Question

• We have fossil evidence that oceans have been around for longer than 180 million years

• It was destroyed by a continuing process- suggests motion of ocean crust

Paleomagnetism

Paleomagnetism

• Study of the Earth’s magnetic record over time

• Many rocks contain magnetic minerals

• When these rocks are hot, the magnetic orientation of the minerals are random

• As they cools, the magnetic orientation of the minerals is fixed in the direction of the magnetic field of earth

What is magnetic orientation?

Means the direction the compass points when moving over the rock

Surprising Data

• Some rocks have a magnetic orientation different from the orientation of Earth

• In the 1960’s researchers mapping the orientation of rock across the Mid Atlantic ridge found a strangely symmetric result

Different colors represent rocks with different magnetic orientation

What has been discovered…

Discovered bands of rock with different magnetic orientation as the ship moves away from ridge

• Evidence that the orientation reverses every 200,000 to several million years

• Matched bands with the same magnetic orientation are found on both sides of a ridge