Geologic Time Scale Quiz

Geologic Time Scale

• Geologists created a scale to divide Earth's 4.6 billion-year history into distinct time intervals.
• The largest divisions are Eons.
• Eons are divided into Eras.
• Eras are divided into Periods.
• Periods are divided into Epochs.
• The boundaries of these time intervals represent major changes in Earth.

Eons

• Hadean Eon: (4.6–3.8 billion years ago)
  • Earliest known rocks on Earth formed during this time.
  • The only rocks from this time are meteorites and rocks from the moon.
• Archean Eon: (3.8–2.5 billion years ago)
  • Earliest known rocks on Earth formed during this time.
• Proterozoic Eon: (2.5 billion–540 million years ago)
  • The first organisms with well-developed cells appeared.
• Phanerozoic Eon: (540 million years ago–Present)
  • The rock and fossil record mainly represents this eon.
  • This is the eon we live in.

Paleozoic Era

• Paleozoic means "old life".
• Lasted from 540 to 248 million years ago
• The first era well-represented by fossils
• Started with the emergence of complex life forms.
• Ended with a major mass extinction.
• Divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian.

Cambrian Period

• First abundant record of marine life (trilobites were dominant).
• Marked a dramatic burst of evolutionary changes.
• Lasted approximately 53 million years.

Ordovician Period

• Characterized by intense diversification of marine life.
• Ordovician radiation led to the appearance of nearly all modern phyla of marine invertebrates.
• Rise of fish also occurred.

Silurian Period

• Continental elevations were generally lower than today, and sea levels were higher.
• Mound-type coral reefs and widespread fishes were common.
• Vascular plants began colonizing coastal lowlands, but continental interiors remained barren.
• Includes the first known terrestrial vascular plants (like Cooksonia).

Devonian Period

• Known as the Age of Fishes, with a remarkable variety.
• Armored fish (placoderms) had powerful jaws.
• First amphibians evolved from fishes.
• Early terrestrial vegetation began to spread.

Carboniferous Period

• Consists of the Mississippian and Pennsylvanian periods.
• Also known as the Coal Age because of alternating land and sea conditions
• Luxuriant forests (including ferns, scale trees, and cordate trees) occurred in coastal lowlands.
• Giant salamanders proliferated as vast forests spread.

Permian Period

• Lasted from 299 to 251 million years ago.
• Last period of the Paleozoic Era.
• Affected many different groups of organisms, but marine communities suffered the most, resulting in a mass extinction.

Mesozoic Era

• Mesozoic means "middle life".
• Lasted from 248 to 66 million years ago.
• Dinosaurs inhabited land and water.
• Divided into three major periods: Triassic, Jurassic, and Cretaceous.
• By the end, around 50% of Earth's species were extinct.

Triassic Period

• First period of the Mesozoic Era.
• Occurred between 251 and 199 million years ago.
• End of the Permian Period mass extinction.
• Rise of first dinosaurs, cycads, and conifers.

Jurassic Period

• Earth's continents were still together (Pangaea), gradually beginning to drift apart.
• Minor extinction at the end of the Triassic period.
• Abundance of dinosaurs.
• First birds and mammals also appeared.
• Includes important dinosaurs like the Brachiosaurus and Stegosaurus.

Cretaceous Period

• The heyday of the dinosaurs.
• Lasted 66 million years ago.
• Ended with a second major mass extinction.
• Marked by dinosaurs with flying reptiles and larger groups of organisms.

Cenozoic Era

• Cenozoic means "new life".
• Began 65 million years ago and continues to the present.
• The Age of Mammals.
• Continents reached modern positions.
• Includes three periods, of which we are most familiar with the Quaternary period.

Tertiary Period

• Consists of five epochs of Paleogene (Paleocene, Eocene, and Oligocene), and Neogene (Miocene and Pliocene)
• Apes diversified and spread across the Old World.
• Kelp forests flourished in the ocean.
• Includes many important early mammal and primate ancestors.

Quaternary Period

• Part of the Cenozoic Era.
• Divided into two epochs- Pleistocene and Holocene.
• Includes dramatic climate changes (glaciations).
• Rise of modern humans.
• Includes important megafauna.