I. Absolute and relative dating

• Absolute dating is a method of estimating the age of an object in years – it uses the known half-life of radioactive materials
• The half-life of an atom is how long it takes half of the atoms to decay
• Relative dating is a method of sequencing events in the order they happened – it determines the age of an object relative to other objects or events in a sequence

II. Geologic Time Scale – a model of the history of life on Earth

• Highlights of life on Earth
• Earth was formed 4.6 billion years ago, starting the Precambrian era
• 3.4 billion years ago, life appeared on Earth (bacteria).
• Modern humans appeared 40,000 years ago.

Precambrian Era – Over 540 million years ago

• No oxygen, rich in other gases – carbon monoxide, carbon dioxide, hydrogen, and nitrogen.
• A lot of chaos – Meteorites crashed into the Earth’s surface; violent thunderstorms and volcanic eruptions were constant; intense Ultraviolet radiation from the sun
• Life started from the chemicals that already existed in the environment.
• As time passed, these chemicals became more and more complex
• Earth was believed to have began 4.6 billion years ago

Paleozioc Era – 540 million – 248 million years ago

Types of Organisms:

• Plants, fungi, air-breathing animals
• All major plants except flowering plants
• Crawling insects and some reptiles
• The Paleozoic era ended with a mass extinction, killing over 90% of marine animals.

Mesozoic Era – 240 million – 65 million years ago

• A giant meteorite (space rock) hit the Earth that generated dust clouds.
• Dust and smoke blocked sunlight.
• Without sunlight, the plants died.
• Without plants, plant-eating animals died.
• Without plant-eating animals, animal-eating animals died.

Types of Organisms

• Dinosaurs
• Giant Marine lizards
• First birds
• Flowering plants

Cenozoic Era – 65 million years ago – today – Age of the Mammals
Types of Organisms

• Mastodons
• Saber-tooth Tigers
• Camels
• Horses
• Humans

III. Fossils
Fossilized organism, trace fossil (footprint, worm trail), cast fossil (organism decays and leaves a mold that minerals fill)

            Rock Cycle

• Igneous – Formed by melting & crystallization, Basalt
• Sedimentary – Formed by sedimentation and compaction, Sandstone
• Metamorphic – Formed by heat and pressure, Marble

• Minerals move through the rock cycle in response to the conditions; weathering, erosion, heat, pressure, etc.

IV. Plate Tectonics

• Earth’s layers from the inside; inner core, outer core, mentle and crust
• Current day continents emerged from Pangea, a supercontinent that has since broken apart
• Plate Boundaries
• Oceanic as well as continental plates

1. Divergent Boundary – plates pulling apart
2. Convergent Boundary – plates coming together
3. Transform Boundary – plates sliding against each other (faults)
4. Subduction Zone – one plate being pushed onder by another