Overview
The lecture traces Earth's 4.5-billion-year history, focusing on the major geological, atmospheric, and biological changes that led to the world we know today.
Formation of Earth and the Moon
- Earth forms from dust and rocks pulled together by gravity nearly 5 billion years ago.
- A Mars-sized object, Theia, collides with Earth, creating debris that forms the Moon.
- Early Earth is a boiling, toxic planet with no oxygen or stable crust.
Early Atmosphere, Water, and Life
- Meteorites bring water and organic molecules, leading to Earth's first oceans.
- Volcanic islands form as molten rock bursts through the crust.
- Primitive bacteria emerge in the oceans, marking the beginning of life.
- Stromatolites (bacterial colonies) drive photosynthesis, releasing oxygen.
The Rise of Oxygen and Changing Continents
- Oxygen builds in oceans, rusting iron and later forming the ozone layer.
- Plate tectonics leads to the creation and breakup of supercontinents like Rodinia and Pangaea.
- Earth's climate swings from "Snowball Earth" ice ages to warm periods.
Cambrian Explosion and Evolution of Life
- After Snowball Earth, life evolves rapidly (Cambrian Explosion), producing complex animals like trilobites and early vertebrates.
- Ozone allows plants to move onto land, increasing oxygen levels further.
- Fish adapt to land, giving rise to amphibians, reptiles, and eventually mammals and birds.
Land Plants, Giant Insects, and Coal Formation
- Seed plants evolve, allowing plants to colonize land away from water.
- High oxygen levels support giant insects and arthropods.
- Decaying plants form thick peat layers buried into coal over millions of years.
Mass Extinctions and Rise of Dinosaurs
- Massive volcanic eruptions cause the Permian extinction, wiping out 95% of species.
- Pangaea forms; as it breaks apart, oil forms from buried plankton.
- Dinosaurs dominate after the extinction, along with early mammals.
Dinosaur Extinction and Mammal Evolution
- A massive asteroid impact 65 million years ago causes dinosaur extinction.
- Mammals survive by burrowing and diversifying, eventually leading to primates.
Continental Drift and Mountain Formation
- Plates continue moving to form modern continents and mountains like the Himalayas.
- India's collision with Asia forms major river systems supporting billions today.
Human Evolution and Ice Ages
- Climate changes in Africa force primates to adapt; upright walking evolves.
- Homo erectus and later Homo sapiens spread globally, colonizing all continents.
- Repeated ice ages shape the landscape and human migration routes.
Modern Earth
- Melting glaciers form features like the Great Lakes.
- The current warm period supports human civilization and the present biosphere.
Key Terms & Definitions
- Plate tectonics — movement of large plates forming Earth's crust, shaping continents and oceans.
- Stromatolites — layered colonies of bacteria, early oxygen producers via photosynthesis.
- Cambrian Explosion — period of rapid diversification of complex life forms about 540 million years ago.
- Ozone layer — atmospheric layer of ozone gas that absorbs harmful solar radiation.
- Permian extinction — the largest mass extinction event, about 250 million years ago.
- Photosynthesis — process where organisms use sunlight to create food and oxygen from carbon dioxide and water.
Action Items / Next Steps
- Review notes on mass extinction events, plate tectonics, and evolutionary milestones.
- Prepare for quiz on key terms (plate tectonics, photosynthesis, Cambrian Explosion, etc.).
- Read assignment: "Evolution of Life on Earth" for more detail on transitions between major eras.