15 - Cenozoic Primates & Climate

Q: What does it mean that if Earth’s history were the length of your arm, humans appear at the tip of the fingernail?

A: Human evolution occupies an extremely tiny fraction of Earth’s total history, emphasizing the vast scale of evolutionary time.

Q: Why does the class begin with “deep time”?

A: To show how long evolutionary processes take and to place human evolution in a much broader biological and geological context.

Q: What major evolutionary events were introduced in this section?

A: Emergence of life, eukaryotes, multicellular life, vertebrates, tetrapods, primates, and hominins.

Q: What are the main components of the Geological Time Scale?

A: Eon → Era → Period → Epoch → Age.

Q: What are the Cenozoic epochs in order?

A: Paleocene (66 Ma), Eocene (56 Ma), Oligocene (34 Ma), Miocene (23 Ma), Pliocene (5 Ma), Pleistocene (2.5 Ma), Holocene (12 kya), Anthropocene (?)

Q: What is plate tectonics?

A: The movement of Earth’s lithospheric plates, which shapes continents, mountain ranges, and ocean basins.

Q: How is rifting formed?

A: Magma rises and pushes the crust apart, creating cracks that split in three directions (tripartite rift).

Q: What are Milankovitch cycles?

A: Cyclical changes in Earth’s orbit/tilt (eccentricity, precession, obliquity) that affect solar radiation and long-term climate.

Q: What is glaciation?

A: Periods when large parts of Earth are covered by ice sheets, controlled by Milankovitch cycles.

Q: How does plate tectonics drive climate change?

A: Alters ocean circulation, volcanic output, mountain building, and greenhouse gas levels.

Q: Why is rifting significant for human evolution?

A: The East African Rift exposes fossils and created the environments where early hominins evolved.

Q: How do scientists identify glacial vs. interglacial periods?

A: Oxygen isotope ratios (O-18/O-16) in ice cores and foraminifera shells.

Q: Who are the earliest primates?

A: Plesiadapiforms—stem primates with some but not all true primate traits.

Q: What climate event marks the boundary between Paleocene and Eocene?

A: The Paleocene–Eocene Thermal Maximum (PETM), a rapid global warming event.

Q: Why was the PETM significant for primates?

A: Warm climates allowed widespread radiation of early primates (adapids & omomyids).

Q: What was the role of continental drift in early primate evolution?

A: Distribution of continents shaped warm ocean currents and tropical conditions that supported primate diversification.

Q: What does the formation of the Antarctic Circumpolar Current do?

A: It isolated Antarctica, cooled the planet, and shifted ecosystems globally.

Q: What primate groups appear in the Fayum (Egypt)?

A: Early anthropoids: propliopithecids, parapithecids, proteopithecids, oligopithecids.

Q: What is the evolutionary significance of the Fayum fossils?

A: They represent the ancestors of platyrrhines (NW monkeys) and catarrhines (OW monkeys + apes).

Q: How did platyrrhines get to the Americas?

A: Rafting hypothesis—floating mats of vegetation from Africa to South America when the distance was ~370 miles.

Q: What happened when Africa collided with Eurasia?

A: Created the Mediterranean Sea, changed ocean circulation, and opened migration routes for apes.

Q: How did the closing of ocean passages affect climate?

A: Shut down warm-water exchange, increased global cooling, changed species ranges.

Q: Why is the Miocene called “Planet of the Apes”?

A: Many ape families emerged and spread through Eurasia.

Q: What caused increased aridity in Africa around 10 Ma?

A: Uplift of Eastern African Highlands blocked moist air → formation of the Sahara.

Q: How did Africa’s uplift contribute to human evolution?

A: Created drier, open environments that favored hominin adaptations like bipedalism.

Q: What role did ocean passage closure play in species migration?

A: Changing sea levels and currents created new land bridges or barriers, influencing primate dispersal.