Unit 5: The Age of Humans and Global Climate Change

The Radiation of Primates

Primates (the group including lemurs, monkeys, apes, and humans) first appeared in the Paleocene/Eocene. They were adapted for an arboreal (tree-dwelling) lifestyle.

Key Primate Adaptations:

• Grasping Hands and Feet: With opposable thumbs for holding onto branches.
• Forward-Facing Eyes: Providing stereoscopic (3D) vision, crucial for judging distances when leaping.
• Large Brains: Relative to body size, for processing complex visual information and social interaction.

This group radiated into the "prosimians" (lemurs) and the "anthropoids" (monkeys and apes). The ape lineage (Hominoids) split from the Old World monkeys around 25-30 Ma.

Human Evolution and the Origin of Homo Sapiens

The human lineage (hominins) split from the chimpanzee lineage around 6-7 Ma in Africa. This was driven by climate change: the forests of Africa began to shrink (see Unit 4), forcing some apes out of the trees and onto the expanding savannas.

Key Steps in Hominin Evolution:

1. Bipedalism (Walking Upright): This was the first major adaptation. It appeared millions of years before large brains.
   • Species: Australopithecus (e.g., the "Lucy" fossil, ~3.2 Ma).
   • Advantage: Freed the hands for carrying food and tools; more efficient way to travel long distances on the savanna.
2. Tool Use:
   • Species: Homo habilis ("Handy Man", ~2.4 Ma).
   • Advantage: The first simple stone tools (Oldowan choppers) allowed for scavenging meat and breaking bones for marrow.
3. Large Brains and Migration:
   • Species: Homo erectus (~1.8 Ma).
   • Advantage: Had a much larger brain, used more advanced tools (Acheulean hand-axes), and was the first hominin to leave Africa, spreading across Asia and Europe.
4. The Origin of Homo sapiens:
   • Species: Homo sapiens (our species) evolved in Africa around 300,000 years ago.
   • We co-existed with other hominin species, such as Neanderthals (in Europe) and Denisovans (in Asia), and even interbred with them.
   • Homo sapiens later migrated "Out of Africa" (~70,000 years ago) and spread across the globe, eventually replacing all other hominin species.

The Climate System: Link Between Climate and Geology

Climate is the long-term average of weather. Geology and Climate are deeply linked; they influence each other over long timescales.

The Climate System Components:

Climate is a complex, interacting system of five spheres:

1. Atmosphere: The gases (N₂, O₂, CO₂) surrounding Earth.
2. Hydrosphere: All liquid water (oceans, lakes, rivers).
3. Cryosphere: All ice (glaciers, sea ice, permafrost).
4. Lithosphere: The solid Earth (rocks, land surface).
5. Biosphere: All living things.