GEOLOGY Chapter 10 Plate Tectonics 10.1 Drifting Continents

10.1 Drifting Continents Objectives Describe one piece of early evidence that led people to suggest that Earth’s continents may have once been joined. Describe one piece of early evidence that led people to suggest that Earth’s continents may have once been joined. Discuss evidence of continental drift. Discuss evidence of continental drift. Explain why continental drift was not accepted when it was first proposed. Explain why continental drift was not accepted when it was first proposed.

Introduction The Earth’s surface is constantly changing. The Earth’s surface is constantly changing. South America is moving away from Africa at a rate of about 2 to 3 cm/y. South America is moving away from Africa at a rate of about 2 to 3 cm/y. The volcanic islands that make up Hawaii are migrating toward the northwest at a rate of 8 to 9 cm/y. The volcanic islands that make up Hawaii are migrating toward the northwest at a rate of 8 to 9 cm/y. Mount Everest is still rising in elevation. Mount Everest is still rising in elevation.

Early Observations In the late 1500s, Abraham Ortelius, a Dutch mapmaker, noticed the apparent fit of continents on either side of the Atlantic Ocean. In the late 1500s, Abraham Ortelius, a Dutch mapmaker, noticed the apparent fit of continents on either side of the Atlantic Ocean. He suggested earthquakes and floods as the mechanism that separated North and South America from Europe and Africa. He suggested earthquakes and floods as the mechanism that separated North and South America from Europe and Africa. Over the next three centuries, many others made this same observation. Over the next three centuries, many others made this same observation. In the late 1800s, Eduard Suess, an Austrian geologist, hypothesized that the present southern continents had once been joined as a single land mass that he called Gondwanaland. In the late 1800s, Eduard Suess, an Austrian geologist, hypothesized that the present southern continents had once been joined as a single land mass that he called Gondwanaland.

Abraham Ortelius (left) and His World Map

Early Observations In 1912, a German scientist named Alfred Wegener presented his ideas about continental movement to the scientific community. In 1912, a German scientist named Alfred Wegener presented his ideas about continental movement to the scientific community. Wegener ( ) earned a PhD in astronomy and made major contributions also to meteorology. Wegener ( ) earned a PhD in astronomy and made major contributions also to meteorology.

Wegener’s hypothesis, called continental drift, proposed that Earth’s continents had once been joined as a single landmass he called Pangaea (Greek for all the earth). Wegener’s hypothesis, called continental drift, proposed that Earth’s continents had once been joined as a single landmass he called Pangaea (Greek for all the earth). Wegener proposed that Pangaea begin to break apart about 200 million years ago. Wegener proposed that Pangaea begin to break apart about 200 million years ago. Wegener collected rock, fossil, and climatic data to add to the fit of continents observed in maps to support his hypothesis. Wegener collected rock, fossil, and climatic data to add to the fit of continents observed in maps to support his hypothesis. Continental Drift

Evidence For Continental Drift Rocks of the Appalachian Mountains in the U.S. share similar features with those found in Greenland and Europe and all are over 200 million years old. Rocks of the Appalachian Mountains in the U.S. share similar features with those found in Greenland and Europe and all are over 200 million years old. Much fossil evidence gathered that support the hypothesis of Pangaea include fossil forms of the same type and age that are found on continents separated by oceans. Much fossil evidence gathered that support the hypothesis of Pangaea include fossil forms of the same type and age that are found on continents separated by oceans. Land dwelling animals and plants with no adaptations for seed dispersal through oceans can only be found on widely separated landmasses if those landmasses were once joined. Land dwelling animals and plants with no adaptations for seed dispersal through oceans can only be found on widely separated landmasses if those landmasses were once joined.

Evidence For Continental Drift Kannemeyerid and Labyrinthodont (top right) could not have swam the great distances between the separated continents on which their remains are now found. Kannemeyerid and Labyrinthodont (top right) could not have swam the great distances between the separated continents on which their remains are now found. Mesosaurus (bottom right) was a freshwater reptile (the type of rock in which it is found indicates so) found in both South America and Africa. Mesosaurus (bottom right) was a freshwater reptile (the type of rock in which it is found indicates so) found in both South America and Africa.

Evidence For Continental Drift Glossopteris (left) is a fossil seed fern found today on a variety of widely separated continents with much different climates. Glossopteris (left) is a fossil seed fern found today on a variety of widely separated continents with much different climates. All of the fossil evidence fit the time frame proposed by Wegener. All of the fossil evidence fit the time frame proposed by Wegener.

Evidence For Continental Drift

Evidence of vast climatic changes on some continents suggested major changes in latitude over time for those landmasses. Evidence of vast climatic changes on some continents suggested major changes in latitude over time for those landmasses. Glossopteris, a seed fern, grew in temperate climates (suggested by plant physiology and matrix) yet it is even found in AntarcticaGlossopteris, a seed fern, grew in temperate climates (suggested by plant physiology and matrix) yet it is even found in Antarctica Coal (forms from dead plants in typically a swampy environment) is also found in Antarctica suggesting a temperate, wet climate in the pastCoal (forms from dead plants in typically a swampy environment) is also found in Antarctica suggesting a temperate, wet climate in the past Glacial deposits are found in southern Africa, India, Australia, and South AmericaGlacial deposits are found in southern Africa, India, Australia, and South America

Evidence For Continental Drift

A Rejected Hypothesis During Wegener’s time, it was strongly believed among the scientific community that the continents and ocean basins were permanently fixed. During Wegener’s time, it was strongly believed among the scientific community that the continents and ocean basins were permanently fixed. Two major flaws prevented Wegener’s hypothesis from being widely accepted. Two major flaws prevented Wegener’s hypothesis from being widely accepted. Wegener could not sufficiently explain what was causing the continents to moveWegener could not sufficiently explain what was causing the continents to move Wegener argued that continents were pushing through the ocean floor, but there was no evidence of fracturing the brittle crustal rockWegener argued that continents were pushing through the ocean floor, but there was no evidence of fracturing the brittle crustal rock

A Rejected Hypothesis The two unanswered questions – “what forces could move continents and how continents could move without shattering” – were the main reasons continental drift was not widely accepted when proposed. The two unanswered questions – “what forces could move continents and how continents could move without shattering” – were the main reasons continental drift was not widely accepted when proposed. Wegener died in 1930 on an expedition to Greenland, but never gave up on his hypothesis. Wegener died in 1930 on an expedition to Greenland, but never gave up on his hypothesis. In the 1960s, new evidence revealed a process that could explain why and how the continents move. In the 1960s, new evidence revealed a process that could explain why and how the continents move.