Stratigraphy, Precambrian & Geological Eras

• Fossil forms occur in rocks.
• Fossil records delineate ages, epochs, and periods.
• Radiometric dating includes thermal ionization mass spectrometry.
• Relative dating is also used.

Principles of Stratigraphy

• Original horizontality: Strata are deposited from above.
• Superposition: Older strata are below younger strata.
• Cross-cutting inclusion: Dike cuts across older rocks.

Precambrian Fossils

• The most common fossils are stromatolites.
• 4.6 billion years ago, there was abundant microscopic life.
• Gases were brought to the surface by volcanic activity.
• Conditions were slowly cooled.
• The atmosphere was very poor in free oxygen.
• Mid-Precambrian: Blue-green algae.

Paleozoic, Mesozoic, and Cenozoic Eras

• Paleozoic: Ancient life.
• Mesozoic: Middle life.
• Cenozoic: Recent life.
• Began about 544 million years ago.
• 300 million years ago.
• Sea levels rose.
• This is divided into six periods.

Cambrian Period

• Calcium carbonate and calcium phosphate were present.
• The Earth was generally cold.
• The period began with an extinction event.
• Example: Elivaia kingli.

Ordovician Period

• There was a rich variety of marine life.
• The first primitive plants began to appear.
• This occurred before the 2nd extinction.
• Example: Lichens.
• Air-breathing scorpions and millipedes were common.
• Fish started becoming more widespread.

Mesozoic Era- Age of Reptiles

• Divided into three periods.

Triassic Period

• The supercontinent of Pangea began to pull apart.
• New kinds of animals evolved after the great extinction at the end of the Permian.
• Rise of dinosaurs.
• Spread of true pines and redwoods.
• Mammals were insignificant.

Jurassic Period

• Warm, tropical greenhouse climate.
• Giant, plant-eating dinosaurs roamed the earth.
• Smaller but vicious flying reptiles and the first birds appeared.
• Mammals replaced reptiles.
• Angiosperms replaced gymnosperms.

Cenozoic Era

• Age of mammals and the flowering plants.
• Made up of two periods.

Tertiary Period, Paleocene Epoch

• Sea fell to expose dry land on much.
• The climate was much warmer and more uniform.
• Evolution proceeded rapidly.