Earth's History and Geologic Time

Study Notes

Earth's history began with the formation of the solar system, encompassing a vast evolutionary timeline.
Geologic time is segmented into four major units: eon, era, period, and epoch.

The geological time scale is a framework for organizing Earth's history and significant events.
Comprised of eons, eras, periods, and epochs that mark important geological and biological events.
Key evidence for this scale comes from the study of rocks and fossils.

Geologists utilize petrology, stratigraphy, and paleontology to reconstruct Earth's history.
Petrology studies the composition, structure, and classification of rocks.
Stratigraphy examines rock layers and their layering processes.
Paleontology analyzes fossils to understand historical life and evolution.

Places rocks and events in chronological order without assigning exact ages.
Methods include:
- Principle of Original Horizontality: sediments settle horizontally.
- Principle of Superposition: older layers are beneath younger ones.
- Principle of Cross-cutting Relationships: features that cut through others are younger.
- Principle of Inclusions: fragments within a rock are older than the rock itself.

Provides actual ages for rocks and events using the decay of radioactive isotopes.
Involves measuring isotopes in fossils and rocks to determine age in years.

Hadean Eon (from the formation, 4600 million years ago):
- Earth's surface was bombarded by meteorites.
- The planet's mantle was extremely hot due to intense volcanism.
- Formation of the solar system from a dust and gas cloud known as the solar nebula.
- Collision of proto-Earth with a planetoid, Theia.
Archean Eon (starting around 3800 million years ago):
- Earth's temperature decreased as it cooled.
- Emergence of photosynthesizing cyanobacteria.
- Addition of gas and water vapor to the atmosphere through volcanic activity.
- Prokaryotes began to appear.
Proterozoic Eon (around 2500 million years ago):
- Abundance of prokaryotes and first emergence of soft-bodied animals.
- Development of the ozone layer.
- Massive extinction of anaerobic organisms.
- Cyanobacteria began to significantly absorb CO2.
Phanerozoic Eon (the current eon with visible life):
- Marked by the fossilization of hard body parts of modern living organisms.
- Split into Paleozoic, Mesozoic, and Cenozoic eras, each representing distinct periods in biological history.