March 14

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