Slides (After Midterm)

Question 1

What is the Cambrian Explosion and why is it significant?

Answer 1

A period (~541 million years ago) when most major animal phyla appeared.
Significant- showing rapid diversification of life forms.

Question 2

What conditions made the Cambrian Explosion possible?

Answer 2

Higher oxygen levels- supported more complex metabolisms and larger body sizes.

Evolution of animals with digestive chambers (metazoans).

Question 3

What is Treptichnus pedum and why is it important?

Answer 3

Treptichnus pedum is a trace fossil marking the Precambrian-Cambrian boundary. It represents burrows left by early metazoan activity and is used as an index fossil for this period.

Question 4

Who was Charles Doolittle Walcott?

Answer 4

A paleontologist who discovered the Burgess Shale fossil deposit in the Canadian Rockies in 1910.

Question 5

What is the significance of the Burgess Shale?

Answer 5

The Burgess Shale contains exceptionally preserved fossils that provide insights into early Cambrian life.

Question 6

Name some iconic organisms found in the Burgess Shale.

Answer 6

Opabinia: Five eyes and a proboscis.

Hallucigenia: Spiny, worm-like creature.

Anomalocaris: Predator with large claws and circular mouth.

Wiwaxia: Armored, slug-like organism.

Marrella: Small arthropod with head spines.

Pikaia: Early chordate.

Question 7

How did Cambrian life evolve over time?

Answer 7

Initially, high diversity among phyla but little variation within each.
Today, fewer phyla with significant variation within them.

Question 8

What caused the Late Cambrian mass extinction?

Answer 8

A sudden drop in marine oxygen levels and toxic hydrogen sulfide (H2S) buildup. This extinction eliminated non-extant phyla, leaving only survivors that persist today.

Question 9

What is taxonomy?

Answer 9

The classification of organisms based on shared traits.

Question 10

What are the “Big Five” mass extinctions?

Answer 10

Late Ordovician (440 Ma)
Late Devonian (365 Ma)
End Permian (245 Ma)
Late Triassic (210 Ma)
End Cretaceous (65 Ma)

Question 11

What factors contribute to mass extinctions?

Answer 11

Rapid environmental changes.
Significant population impacts.
Massive biodiversity collapses across multiple lineages.

Question 12

How do mass extinctions impact biodiversity?

Answer 12

Mass extinctions reduce the variety of life, hitting species with specific roles the hardest. They create opportunities for new traits to evolve and for life to diversify again.

Question 13

What are internal and external causes of extinction?

Answer 13

Internal: Habitat changes, disease, microbial evolution.

External: Impacts, climate changes (warming or cooling), tectonic activity, and supernova gamma-ray bursts.

Question 14

What is taphonomy?

Answer 14

The study of everything that happens to an organism from death to discovery as a fossil.

Question 15

Terrestrial (non-marine) fossils are found where?

Answer 15

In rocks, lakes beds, peat bogs, marshes, & tar pits

Question 16

Why are Terrestrial (non-marine) fossils less common than marine fossils?

Answer 16

due to erosion scavenging and fewer species

Question 17

True/False
Most of all fossils are from marine environments

Answer 17

True

Question 18

Why are Marine fossils mostly found?

Answer 18

70% of Earth’s surface is ocean. Marine conditions favor rapid burial and preservation compared to terrestrial environments.

Question 19

How are natural selection and extinction related?

Answer 19

Natural selection helps species survive by favoring traits that are useful, while extinction happens when species can’t adapt to changes in their environment. Mass extinctions, however, wipe out many species at once, regardless of their roles in the ecosystem.

Question 20

What are key facts about Tyrannosaurus rex?

Answer 20

Time Period: 68-66 Ma.

Role: Apex predator and scavenger.

Habitat: North America, from semi-arid to subtropical regions.

Population: ~2.5 billion individuals over 127,000 generations.

Question 21

Paleontology: study of ancient life through fossils provides information on:

Answer 21

• Evolution of life & ecosystems on Earth
• Catastrophic events: mass extinctions, volcanic eruptions, impacts

Question 22

What is the supercontinent cycle, and who proposed it?

Answer 22

The supercontinent cycle describes the repeated process of supercontinents forming, breaking apart, and reassembling every ~500 million years (Ma). It was proposed by J. Tuzo Wilson. The cycle involves tectonic processes such as rifting, seafloor spreading, subduction, and continental collision.

Question 23

Name and describe four key supercontinents from Earth’s history.

Answer 23

Columbia (Nuna): Formed ~1.7 billion years ago (Ga).

Rodinia: Preceded Pangaea, existing ~1.1-0.7 Ga.

Gondwana: A long-lasting assembly of southern continents, including South America, Africa, India, Antarctica, and Australia.

Pangaea: The most recent supercontinent (~335-175 Ma), comprising Laurasia (northern continents) and Gondwana.

Question 24

What are three major ancient oceans, and where were they located?

Answer 24

Panthalassa: The global ocean surrounding Pangaea.

Iapetus Ocean: Precursor to the Atlantic Ocean, separating Laurentia (proto-North America) from Gondwana.

Tethys Ocean: An equatorial ocean between Gondwana and Laurasia.

Question 25

What happens in the first step of the supercontinent cycle?

Answer 25

Existing supercontinents break apart due to hot, uplifting continental crust. This rifting creates rift valleys, which eventually fill with seawater.

Question 26

What characterizes the second step of the supercontinent cycle?

Answer 26

Formation of "Atlantic-type" oceans. Active seafloor spreading forms mid-ocean ridges (MORs), which displace water onto continental shelves, causing sea level rise.

Question 27

What happens in step three of the supercontinent cycle?

Answer 27

Subduction zones develop as dense oceanic lithosphere is consumed. Atlantic-type oceans transition into Pacific-type oceans. Broad, shallow epeiric seas cover continents due to displaced water.

Question 28

What happens in step four of the supercontinent cycle?

Answer 28

Closure of Pacific-type ocean basins and the formation of a new supercontinent. Continental collisions slow seafloor spreading, causing sea levels to drop as ocean floors cool and sink.

Question 29

Describe the fifth and final step of the supercontinent cycle.

Answer 29

The newly formed supercontinent remains stable for ~100 million years. Heat accumulates underneath, eventually leading to renewed rifting.

Question 30

What are the five key tectonic events along the East Coast of North America?

Answer 30

Grenville Orogeny: Formation and breakup of Rodinia (~1 Ga). Taconic Orogeny: Accretion of the Taconic arc during the Ordovician. Acadian Orogeny: Devonian accretion of Avalonia. Alleghanian Orogeny: Pennsylvanian-Permian collision with Africa and South America. Rifting: Triassic breakup of Pangaea and formation of the Atlantic Ocean.

Question 31

Highlight major tectonic events on the West Coast of North America.

Answer 31

Neoproterozoic: Rifting during the breakup of Rodinia. Antler Orogeny: Devonian accretion of a volcanic arc. Nevadan Orogeny: Triassic east-directed subduction builds Sierra Nevada. Sevier Orogeny: Jurassic-Cretaceous thin-skinned deformation. Laramide Orogeny: Paleogene flat-slab subduction causes thick-skinned deformation. Basin and Range Extension: Miocene transtension creates extensional basins.

Question 32

What is the difference between thin-skinned and thick-skinned deformation?

Answer 32

Thin-Skinned: Only involves sedimentary cover layers above a detachment fault, forming fold-thrust belts. Thick-Skinned: Includes basement rocks and cover layers, with deformation reactivating old basement structures.

Question 33

What caused the Ancestral Rockies to form, and what remains of them today?

Answer 33

The Ancestral Rockies formed during the Permian due to stresses from the collision between North America, Africa, and South America. The uplifts have eroded away, but sediments remain in adjacent basins.

Question 34

Define "orogen" and "clastic wedge."

Answer 34

Orogen: A mountain-building region formed by tectonic forces. Clastic Wedge: Sediments deposited adjacent to an eroding mountain range, providing a record of its history.

Question 35

What might happen to the San Andreas Fault in the future?

Answer 35

The "big bend" in the San Andreas Fault will likely lock up, and a new plate boundary may form east of the Sierra Nevada.

Question 36

What are the three major periods of diversification during the Phanerozoic?

Answer 36

Cambrian Explosion: Rapid divergence of modern phyla. Ordovician Radiation: Paleozoic fauna replaced Cambrian fauna. Mesozoic-Cenozoic Radiation: Modern fauna diversified.

Question 37

What are the "Big 5" mass extinctions?

Answer 37

End-Ordovician, End-Devonian, Permo-Triassic, End-Triassic, and End-Cretaceous.

Question 38

What were trilobites, and why are they important?

Answer 38

Trilobites were dominant arthropods during the Cambrian and excellent index fossils due to their rapid evolution and diverse morphologies.

Question 39

What organisms contributed to Paleozoic reef ecosystems?

Answer 39

Rugose and tabulate corals, stromatoporoids, and other reef-builders created structures that enabled marine biodiversity.

Question 40

What is the significance of articulate brachiopods?

Answer 40

Articulate brachiopods have toothed hinges and simple muscles for opening and closing, contributing to Paleozoic biodiversity.

Question 41

What defines modern evolutionary fauna?

Answer 41

Modern evolutionary fauna includes bivalves, echinoids, gastropods, crustaceans, and vertebrates. They became dominant after the Permo-Triassic extinction.

Question 42

What biases exist in paleodiversity studies?

Answer 42

Biases include rock record availability, taxonomy, geographical sampling, and the "pull of the recent," where modern taxa are better preserved and studied.

Question 43

What is the significance of small shelly fauna?

Answer 43

Early organisms experimenting with hard parts, such as hyoliths, paving the way for more complex skeletal structures in marine life.

Question 44

What adaptations helped Paleozoic fauna thrive?

Answer 44

Sessile filter feeding, toothed hinges for protection, and complex reef-building contributed to their dominance.

Question 45

What are Bryoans and their significance?

Answer 45

Sessile flter-feeding organisms that form fan-, brush-, & sheetshaped colonies * Closely related to brachiopods – only Phylum to appear AFTER Cambrian * Very abundant in Paleozoic, still common today

Question 46

What are Bivalves?

Answer 46

Marine & freshwater flter-feeding (mostly) mollusks enclosed in hinged shells that live in burrows, attached to substrates, or freeswimming

Question 47

What are Echinoids?

Answer 47

sea urchins- spiny echinoderms (shell/ skeleton) that closely resemble modern forms

Question 48

Gastropods

Answer 48

Extremely diverse Class of mollusks marine & freshwater limpets, snails, & slugs * Good index fossil: coiled or spiral