GEOLOGYGEOLOGY

Chapter 10 Plate TectonicsChapter 10 Plate Tectonics

10.1 Drifting Continents10.1 Drifting Continents

10.1 Drifting Continents10.1 Drifting ContinentsObjectivesObjectives

Describe one piece of early evidence Describe one piece of early evidence that led people to suggest that that led people to suggest that Earth’s continents may have once Earth’s continents may have once been joined.been joined.

Discuss evidence of continental drift.Discuss evidence of continental drift. Explain why continental drift was not Explain why continental drift was not

accepted when it was first proposed.accepted when it was first proposed.

IntroductionIntroduction

The Earth’s surface is constantly The Earth’s surface is constantly changing.changing.

South America is moving away from South America is moving away from Africa at a rate of about 2 to 3 cm/y.Africa at a rate of about 2 to 3 cm/y.

The volcanic islands that make up The volcanic islands that make up Hawaii are migrating toward the Hawaii are migrating toward the northwest at a rate of 8 to 9 cm/y.northwest at a rate of 8 to 9 cm/y.

Mount Everest is still rising in Mount Everest is still rising in elevation.elevation.

Early ObservationsEarly Observations In the late 1500s, Abraham Ortelius, a Dutch In the late 1500s, Abraham Ortelius, a Dutch

mapmaker, noticed the apparent fit of continents mapmaker, noticed the apparent fit of continents on either side of the Atlantic Ocean.on either side of the Atlantic Ocean.

He suggested earthquakes and floods as the He suggested earthquakes and floods as the mechanism that separated North and South mechanism that separated North and South America from Europe and Africa.America from Europe and Africa.

Over the next three centuries, many others made Over the next three centuries, many others made this same observation.this same observation.

In the late 1800s, Eduard Suess, an Austrian In the late 1800s, Eduard Suess, an Austrian geologist, hypothesized that the present southern geologist, hypothesized that the present southern continents had once been joined as a single land continents had once been joined as a single land mass that he called Gondwanaland.mass that he called Gondwanaland.

Abraham Ortelius (left) and His Abraham Ortelius (left) and His World MapWorld Map

Early ObservationsEarly Observations In 1912, a German In 1912, a German

scientist named Alfred scientist named Alfred Wegener presented Wegener presented his ideas about his ideas about continental movement continental movement to the scientific to the scientific community.community.

Wegener (1880-1930) Wegener (1880-1930) earned a PhD in earned a PhD in astronomy and made astronomy and made major contributions major contributions also to meteorology.also to meteorology.

Wegener’s hypothesis, called continental Wegener’s hypothesis, called continental drift, proposed that Earth’s continents had drift, proposed that Earth’s continents had once been joined as a single landmass he once been joined as a single landmass he called Pangaea (Greek for called Pangaea (Greek for all the earthall the earth).).

Wegener proposed that Pangaea begin to Wegener proposed that Pangaea begin to break apart about 200 million years ago.break apart about 200 million years ago.

Wegener collected rock, fossil, and Wegener collected rock, fossil, and climatic data to add to the fit of continents climatic data to add to the fit of continents observed in maps to support his observed in maps to support his hypothesis.hypothesis.

Continental DriftContinental Drift

Evidence For Continental DriftEvidence For Continental Drift Rocks of the Appalachian Mountains in the U.S. Rocks of the Appalachian Mountains in the U.S.

share similar features with those found in share similar features with those found in Greenland and Europe and all are over 200 Greenland and Europe and all are over 200 million years old.million years old.

Much fossil evidence gathered that support the Much fossil evidence gathered that support the hypothesis of Pangaea include fossil forms of the hypothesis of Pangaea include fossil forms of the same type and age that are found on continents same type and age that are found on continents separated by oceans.separated by oceans.

Land dwelling animals and plants with no Land dwelling animals and plants with no adaptations for seed dispersal through oceans adaptations for seed dispersal through oceans can only be found on widely separated can only be found on widely separated landmasses if those landmasses were once landmasses if those landmasses were once joined.joined.

Evidence For Continental DriftEvidence For Continental Drift Kannemeyerid Kannemeyerid and and

Labyrinthodont Labyrinthodont (top right)(top right) could not have swam the could not have swam the great distances between great distances between the separated continents the separated continents on which their remains are on which their remains are now found.now found.

MesosaurusMesosaurus (bottom right) (bottom right) was a freshwater reptile was a freshwater reptile (the type of rock in which it (the type of rock in which it is found indicates so) is found indicates so) found in both South found in both South America and Africa.America and Africa.

Evidence For Continental DriftEvidence For Continental Drift

GlossopterisGlossopteris (left) is a (left) is a fossil seed fern found fossil seed fern found today on a variety of today on a variety of widely separated widely separated continents with much continents with much different climates.different climates.

All of the fossil All of the fossil evidence fit the time evidence fit the time frame proposed by frame proposed by Wegener.Wegener.

Evidence For Continental DriftEvidence For Continental Drift

Evidence For Continental DriftEvidence For Continental Drift

Evidence For Continental DriftEvidence For Continental Drift

Evidence of vast climatic changes on some Evidence of vast climatic changes on some continents suggested major changes in continents suggested major changes in latitude over time for those landmasses.latitude over time for those landmasses.• GlossopterisGlossopteris, a seed fern, grew in temperate , a seed fern, grew in temperate

climates (suggested by plant physiology and climates (suggested by plant physiology and matrix) yet it is even found in Antarcticamatrix) yet it is even found in Antarctica

• Coal (forms from dead plants in typically a Coal (forms from dead plants in typically a swampy environment) is also found in swampy environment) is also found in Antarctica suggesting a temperate, wet climate Antarctica suggesting a temperate, wet climate in the pastin the past

• Glacial deposits are found in southern Africa, Glacial deposits are found in southern Africa, India, Australia, and South AmericaIndia, Australia, and South America

Evidence For Continental DriftEvidence For Continental Drift

A Rejected HypothesisA Rejected Hypothesis

During Wegener’s time, it was strongly During Wegener’s time, it was strongly believed among the scientific community believed among the scientific community that the continents and ocean basins were that the continents and ocean basins were permanently fixed.permanently fixed.

Two major flaws prevented Wegener’s Two major flaws prevented Wegener’s hypothesis from being widely accepted.hypothesis from being widely accepted.• Wegener could not sufficiently explain what Wegener could not sufficiently explain what

was causing the continents to movewas causing the continents to move• Wegener argued that continents were pushing Wegener argued that continents were pushing

through the ocean floor, but there was no through the ocean floor, but there was no evidence of fracturing the brittle crustal rockevidence of fracturing the brittle crustal rock

A Rejected HypothesisA Rejected Hypothesis

The two unanswered questions – “what The two unanswered questions – “what forces could move continents and how forces could move continents and how continents could move without shattering” continents could move without shattering” – were the main reasons continental drift – were the main reasons continental drift was not widely accepted when proposed.was not widely accepted when proposed.

Wegener died in 1930 on an expedition to Wegener died in 1930 on an expedition to Greenland, but never gave up on his Greenland, but never gave up on his hypothesis.hypothesis.

In the 1960s, new evidence revealed a In the 1960s, new evidence revealed a process that could explain why and how process that could explain why and how the continents move.the continents move.