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Questions and Answers
What significant event characterized the end of the Mesozoic Era?
What significant event characterized the end of the Mesozoic Era?
During which epoch did major changes such as the global expansion of grasslands occur?
During which epoch did major changes such as the global expansion of grasslands occur?
Which of the following ecosystems first appeared during the Miocene epoch?
Which of the following ecosystems first appeared during the Miocene epoch?
What is one of the primary changes during the Pliocene epoch related to tectonic activity?
What is one of the primary changes during the Pliocene epoch related to tectonic activity?
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What major climate event characterizes the Quaternary Period?
What major climate event characterizes the Quaternary Period?
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During the Miocene epoch, what significant evolutionary event occurred involving early humans?
During the Miocene epoch, what significant evolutionary event occurred involving early humans?
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Which plants dominated the landscape during the Oligocene epoch?
Which plants dominated the landscape during the Oligocene epoch?
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What immediately follows the Neogene Period in geological time?
What immediately follows the Neogene Period in geological time?
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What is the Mesozoic Era often referred to as?
What is the Mesozoic Era often referred to as?
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During which period did the Mesozoic Era begin?
During which period did the Mesozoic Era begin?
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Which significant geological event occurred during the Mesozoic Era?
Which significant geological event occurred during the Mesozoic Era?
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What type of vegetation primarily spread during the Devonian period?
What type of vegetation primarily spread during the Devonian period?
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Which of the following best describes the Pennsylvanian Period?
Which of the following best describes the Pennsylvanian Period?
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What was a significant outcome by the end of the Mesozoic Era?
What was a significant outcome by the end of the Mesozoic Era?
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What type of trees were prevalent during the forests of the Pennsylvanian Period?
What type of trees were prevalent during the forests of the Pennsylvanian Period?
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What significant event marked the beginning of the Jurassic Period?
What significant event marked the beginning of the Jurassic Period?
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Which dinosaur is mentioned as flourishing during the Jurassic Period?
Which dinosaur is mentioned as flourishing during the Jurassic Period?
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During which period did the Cretaceous-Paleogene (K-Pg) extinction event occur?
During which period did the Cretaceous-Paleogene (K-Pg) extinction event occur?
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What is the Cenozoic era often referred to as?
What is the Cenozoic era often referred to as?
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What major characteristic defines the Jurassic Period?
What major characteristic defines the Jurassic Period?
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Which of the following rock types is associated with the Cretaceous Period's name?
Which of the following rock types is associated with the Cretaceous Period's name?
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What occurred to Earth's continents during the Jurassic Period?
What occurred to Earth's continents during the Jurassic Period?
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Which epoch marked the beginning of the Cenozoic era?
Which epoch marked the beginning of the Cenozoic era?
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Study Notes
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.
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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.
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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.
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Description
Test your knowledge about the Geologic Time Scale, including the various Eons, Eras, Periods, and Epochs that mark Earth's 4.6 billion-year history. Explore how geologists classify significant changes in our planet's history into distinct intervals. Challenge yourself on the details of each eon and era!
