Unit 4: History of Earth and Human Society Week 13

Anthropocene

A proposed geological time period defined by significant human impact on Earth's ecosystems, climate, and biodiversity

Major threats to biodiversity

Habitat loss, climate change, overexploitation, invasive species, and pollution

Habitat loss

Destruction of ecosystems that removes resources organisms need to survive

Habitat fragmentation

Breaking large habitats into smaller isolated patches, reducing gene flow and increasing extinction risk

Pollution

Introduction of harmful substances (toxins, plastics, chemicals) that affect survival and reproduction

Overexploitation

Unsustainable use of species through hunting, fishing, and logging leading to population decline

Invasive species

Non-native species that spread rapidly and outcompete native species

Ecosystem engineer (humans)

Organisms that significantly modify environments and resource availability on a global scale

Homo sapiens origin

Evolved about 200,000-300,000 years ago in Africa

Out of-Africa hypothesis

Modern humans evolved in Africa and migrated outward, replacing other hominins

Savanna hypothesis

Early humans adapted to open grasslands due to climate change

Key human traits

Bipedalism, tool use, large brains, and social cooperation

Climate variability hypothesis

Changing environments favored adaptability and intelligence in humans

Human population growth type

Exponential growth

Great Acceleration

Rapid increase in population, energy use, and environmental impact after WWII

Current population trend

Population is still increasing but growth rate is slowing

Ecological footprint

The amount of land and resources used by a person or population

Earth formation

Occurred about 4.6 billion years ago

Earliest life

Anaerobic prokaryotes in oceans

Great Oxygenation Event

Rise in atmospheric oxygen caused by cyanobacteria photosynthesis

Importance of oxygen

Allowed complex life and caused extinction of many anaerobic organisms

Eukaryote evolution

Occurred through endosymbiosis (engulfing cells that became mitochondria and chloroplasts)

Cambrian Explosion

Rapid diversification of multicellular life around 541 million years ago

Colonization of land

Occurred about 467-350 million years ago

Environmental changes effect on life

Drive evolution, adaptation, speciation, and extinction

Biological impact on Earth

Organisms can change Earth's environment (e.g., oxygen production by cyanobacteria)

Woody plants impact

Reduced atmospheric CO₂ levels significantly

Life-environment relationship

Life and environment influence each other through continuous feedback loops