pangea and continental drift mr. white 6 th grade earth science

Pangea and Continental Drift

Mr. White

6th Grade Earth Science

Alfred Wegener Born: Germany, 1880 PhD: Astronomy Profession: Meteorologist and Greenland Explorer Died: 1930

Became the “father of continental drift” by amassing considerable supporting evidence that the continents moved over time

In 1915 Wegener published his work in The Origin of the Continents and Oceans.

Continental DriftWegener was the first to advance the idea of mobile continents in 1912

He identified several lines of evidence to support the idea that the continents had drifted

What was the evidence and where did it come from?

1- Continental shape

2- Fossil remains3- Sea Floor Depth (Global Bathymetry- SONAR)

4- Magnetic Stripes –A geomagnetic reversal is a change in the Earth's

magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was in the opposite direction.

5- Paleoclimatology

6 - Mountain Soil Comparison

Evidence for continental drift

Matching coastlines on different continents


Distribution of fossils such as Mesosaurus

Figure 2-6

Early Case for Continental Drift• Puzzle-piece fit of coastlines of Africa and

South America has long been known

• In early 1900s, Alfred Wegener noted South America, Africa, India, Antarctica, and Australia have almost identical late Paleozoic rocks and fossils– Glossopteris (plant), Lystrosaurus and

Cynognathus (animals) fossils found on all five continents

– Mesosaurus (reptile) fossils found in Brazil and South Africa only

Early Case for Continental Drift• Wegener reassembled continents into the

supercontinent Pangaea• Pangea initially separated into Laurasia and

Gondwanaland – Laurasia - northern supercontinent containing North

America and Asia (excluding India)– Gondwanaland - southern supercontinent containing South

America, Africa, India, Antarctica, and Australia

• Late Paleozoic glaciation patterns on southern continents best explained by their reconstruction into Gondwanaland

• Coal beds of North America and Europe support reconstruction into Laurasia

The presence of fossils only over small areas of now separate continents (how did they get from continent to continent?).


Matching mountain ranges across oceans

300 million years agoToday

Ancient “cratons” within continents match up when they are brought together like a jigsaw puzzle.

Mountain formations were once connected


Glacial ages and climate evidence

Objections to the continental drift model

Wegener envisioned continents plowing through ocean basins

Wegener did not provide a plausible mechanism to explain how the continents could have drifted apart

Most Earth scientists rejected continental drift because it was

Too far-fetched

Contrary to the laws of physics

The theory of plate tectonics

Continental drift was reexamined in the 1960s when new information became available

Sea floor features became better known

A technique was developed that enabled scientists to determine the original positions of rocks on Earth (paleomagnetism)

Evidence for plate tectonics

Earth’s magnetic field affects all magnetic objects on Earth

Figure 2-7


When rocks cool at Earth’s surface, they record Earth’s magnetic field (normal or reversed polarity)

Figure 2-9


Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge

Pattern was created by sea floor spreading

Figure 2-11


Harry Hess envisioned new sea floor being created at the mid-ocean ridge and destroyed in deep ocean trenches

Figure 2-10


Age of the sea floor matches pattern predicted by sea floor spreading

Youngest sea floor is at mid-ocean ridgeSea floor is older with increasing distance from mid-ocean ridge

Figure 2-12


Pattern of worldwide earthquakes (left) matches plate boundaries (right)

Figure 2-13

Earth structureChemical composition

CrustMantleCore

Physical propertiesLithosphereAsthenosphereMesosphereOuter coreInner core Figure 2-14

Principles of plate tectonics

The outermost portion of Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another

Plates interact with each other along their edges (called plate boundaries)

Plate boundaries have a high degree of tectonic activity (mountain building, earthquakes, active volcanoes)

The 3 types of plate boundaries

1. Divergent

2. Convergent

3. Transform

Figure 2-17

Divergent plate boundaries

The Mid-Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs Figure 2-18


Iceland sits atop a divergent plate boundary where continental rifting occurs

Figure 2-19


Formation of an ocean basin by rifting and sea floor spreading

Figure 2-20

Convergent plate boundaries

Convergent plate boundaries vary depending on the type of crust

Figure 2-23

a. Ocean-continent

b. Ocean-ocean

c. Continent-continent


An ocean-continent convergent plate boundary produces the Cascadia subduction zone and Cascade Mountains

Figure 2-24


A continent-continent convergent plate boundary produces the Himalaya Mountains

Figure 2-25

Transform plate boundaries

Transform plate boundaries occur between segments of the mid-ocean ridgeCan also occur on land (ex: San Andreas Fault)

Figure 2-26

Hotspots and plate tectonics

Hotspots are stationary and have abundant volcanic activityThe lithospheric plate moves over the hotspotCreates a row of volcanoes progressively older toward one end (called a nematath)

Figure 2-28

Stages of coral reef development

If in tropical shallow water, coral reefs can form on the tops of volcanoes

Fringing reefBarrier reefAtoll Figure 2-30

Atoll and barrier reefs in the Society Islands

Figure 2-32

Satellite positioning of locations on Earth

Shows good agreement with predicted plate motion

Figure 2-33

Paleogeography: A look at the past

The positions of continents and oceans have changed in the past

Internet site showing more detailed maps

Figure 2-34

The world as it may look 50 million years in the future

Figure 2-35

End of Chapter 2

Essentials of Oceanography

7th Edition

pangea and continental drift mr. white 6 th grade earth science

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