Historical Geology

Flashcards covering key concepts from the Historical Geology lecture notes.

What processes have historically affected the distribution of organisms on Earth?

Continents moving, seas expanding and contracting, mountain ranges rising and eroding, islands appearing and disappearing, glaciers advancing and retreating, and variation in the width of tropics.

Rate of Sedimentation

Process of estimating the age of fossils by measuring the layers of sedimentary rock above and below them, to determine the time period the fossils formed. (Oldest fossils at the bottom)

When did Wallace accept the age of earth

400 million years

Radioisotope (More accurate than rate of sedimentation)

Used to determine the age of fossils by measuring the decay of radioactive isotopes in the sedimentary rock or the fossil itself.

Which radioisotopes are used to determine the age of fossils?

Uranium, thorium, potassium-argon, and carbon

Which radioisotope is used for younger fossils?

Carbon- up to 60,000 years

Who’s radioisotopes are used for determining the age of older fossils?

Potassium-argon and Uranium

What is the estimated age of the Earth based on radioisotope dating?

4.6 billion years.

What significant event is associated with the K/T-Boundary?

The Earth was struck by a 6-mile wide asteroid, resulting in mass extinction.

Evidence of continental drift

Lungfish distributed in South America, Africa, and Australia

Who first proposed the hypothesis of Continental Drift?

Alfred Wegener.

What did Alfred Wegener predict?

Predicted that landmasses were once a contiguous continent (Pangea) that broke into smaller continental plates. Mid- oceanic ridges mark where continents were joined and ocean trenches formed as continental blocks moved.

What is the rate of movement of landmasses?

0.3-36 meters per year

What was Pangaea?

A large continent that existed when all landmasses were joined together, which later broke apart into smaller continental plates.

What are the two halves of the Earth during the Triassic period called?

Laurasia in the Northern Hemisphere and Gondwanaland in the Southern Hemisphere.

When did Pangea (Permian period) break up?

Early Jurassic (180 million years ago)

What major tectonic event occurred 100 million years ago?

The breakup of Laurasia by mid-Cretaceous

When did the break up of Gondwanaland occur?

Early Jurassic 180 million years ago. Madagascar and India 130 mya. 4 landmasses 125 mya: South America, Africa, Madagascar-India, Antarctica-Australia-NZ. 100 mya Australia and NZ rifted from antartica. 60 mya India and Madagascar separate and India collides with Eurasia, forming the Himalayas.

How was Central America formed?

Late Jurassic (150 mya) Mexico and SA separate. Early Cretaceous (120-140 mya) Antilles form a chain of volcanic islands. Central American land bridge emerged late Cretaceous (80-65 mya)-resulted in great American interchange.

Formation of Mediterranean Sea

Africa swung counterclockwise toward Eurasia closing the Tethys sea. A bridge was formed between Asia and Africa through Arabia (35 mya)

Formation of the Red Sea

Formed by rifting

This rift system continues south to form the great rift valley. Lakes Victoria, tanganyika, etc.may eventually become an inland seaway continuous with the Indian Ocean. (35 mya)

Define rifting

The breaking or separation through faulting caused by tectonic plates.

What environmental changes are associated with glaciation?

Temperature cooling, changes in sea level, habitat configurations, and alterations in climatic and environmental zones.

Glaciation and extinctions

First extinctions were plants. Decoupling of plants with animal pollinators. Later glacial periods in Pleistocene saw many large mammal extinctions.

What is a possible biotic response to glaciation?

“Floating” distribution Moving with optimal habitat, adapting to environmental changes, or range reduction and extinction.

What is the 'Overkill Hypothesis'?

It states that humans are responsible for the mass extirpation of large herbivores, carnivores, and scavengers after the last glacial retreat. (18,000 yr ago)

What evidence supported the overkill hypothesis?

Fossil evidence suggested humans and mammals coexisted with hunting practices, extinctions were non-random (large animals over small), Eurasian animal immigrants like sheep, moose, deer, and dall’s sheep fared better than native species. Extinctions north to south.

What problems are associated with the Overkill Hypothesis?

Extinctions were underway before humans arrived; coexistence of aggressive hunters with large mammals; human populations were not at high densities. Not all extinctions on other continents corresponded with humans. Multiple plant and animal extinctions all at once.

What is the climatic explanation?

Direct cause of extinction through increased aridity (lack of moisture).

What does the Climatic Hypothesis suggest about extinctions?

Extinctions had begun before the end of the Ice Age and were a continuing series of episodes, affecting both large and small mammals.

What is a notable contradiction regarding the timing of megafaunal extinctions?

Megafauna diversified during unfavorable climatic conditions but suffered extinctions when conditions became more favorable, because of human hunters and rapid, unstable environmental changes..

Why did megafauna extinctions not occur during earlier glaciations?

During earlier glacial cycles, megafauna survived because of less extreme pressures from humans or environmental changes.

Why were smaller mammals better at surviving?

Their smaller size allowed them to have better shelter, less dietary restraints, lower caloric needs (can survive on little food).

Why did megafauna in Africa not go extinct?

They had more time to adapt to the human hunters by cohabiting with human ancestors.

According to George Gaylord Simpson, what is critical to curtailing present extinctions?

Understanding and learning the lessons of prehistoric extinctions.