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Questions and Answers
The Paleozoic Era is divided into seven periods.
False
The Cambrian Period is known for the Cambrian Explosion, which occurred approximately 541 million years ago.
True
During the Ordovician Period, the first vascular plants appeared on land.
False
The Silurian Period is notable for the development of the first jawed fish, known as Placoderm.
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The Devonian Period is often referred to as the 'Age of Insects' due to the high diversity of insect life.
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During the Carboniferous Period, forests with seed plants dominated the landscape.
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Trilobites were among the first terrestrial arthropods that appeared during the Devonian Period.
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The major extinction event at the end of the Ordovician Period led to the extinction of approximately 60% of marine species.
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The Precambrian Eon is the current geologic eon in the geologic time scale.
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The Hadean Eon occurred from 4.6 to 4 billion years ago.
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Cyanobacteria evolved at least 1 billion years ago.
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The Paleozoic Era is characterized by the emergence of many major animal groups.
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The Proterozoic Eon started 1 billion years ago.
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The Phanerozoic Eon covers the period from 541 million years ago to the present.
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The Archean Eon is known as the 'age of hidden life.'
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During the Archean Eon, the ocean floor was covered in a living mat of animal life.
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The collision of continents to form Pangaea resulted in the expansion of inland seas.
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Ichthyostega was an early amphibian that lived predominantly in aquatic environments.
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The Late Permian and early Triassic periods are associated with one of the most significant extinction events in Earth's history.
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Dinosaurs first appeared during the Jurassic period.
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Archaeopteryx is considered the first bird that appeared during the Cretaceous period.
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The Cenozoic Era is often referred to as the 'Age of Mammals' due to the extinction of many large mammal groups.
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The first flowering plants appeared during the Cretaceous period.
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Eocasea was one of the first vertebrate herbivores to appear on land.
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Study Notes
Geologic Time Scale
- A timeline that organizes Earth's history based on geological events and life forms
- A system that chronologically relates geological strata (stratigraphy) to time.
Major Divisions of the Geologic Time Scale
- Eon: The largest span of time on the geologic time scale
Eon Divisions
- Precambrian Eon: Refers to the earliest part of Earth’s history.
- Phanerozoic Eon: The current geologic eon.
Precambrian Eon Subdivisions
-
Hadean Eon: Occurred 4.6 – 4 billion years ago
- The solar system was forming within a cloud of dust and gas known as the solar nebula
- The earth started cooling and the outer edge of the planet solidified from molten lava to a solid crust
- Water rained from the atmosphere and created oceans.
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Archean Eon: 4 – 2.5 billion years ago
- First life forms were created in the oceans
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Proterozoic Eon: "The age of hidden life"
- Started 2.5 billion years ago
- Enough shield rock had formed to start recognizable geological processes such as plate tectonics
- Fossil remains of bacteria are present.
- Blue-green algae emerged.
- The first oxygen-dependent animals, Ediacara fauna, appeared.
Archean Subdivisions
-
Cyanobacteria: Evolved at least 2 billion years ago
- Earth's first photosynthetic bacteria, using water and the Sun's energy, and releasing oxygen as a result.
Phanerozoic Eon
- Abundance of animal and plant life existed
- Covers 541 million years to the present.
Phanerozoic Eon Subdivisions
-
Paleozoic Era: 542 – 251 million years ago
- Known as the “ancient life”
- Characterized by the diversification of life on Earth, with the emergence of many major animal groups.
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Mesozoic Era: 252 – 66 million years ago
- Known as the age of reptiles/dinosaurs
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Cenozoic Era: 65 million years ago – present
- The current locations of the continents and their modern-day inhabitants, including humans, can be traced to this period.
Paleozoic Era Subdivisions
-
Cambrian Period: 541-485 million years ago
- Cambrian Explosion: a period of rapid diversification of life.
- Appearance of hard-shelled organisms.
- Predation emerged.
- Trilobites (arthropods with hard exoskeletons) appeared
- Brachiopods (filter-feeding marine animals with two shells) appeared
- Crinoids (sea lilies, related to starfish, sea urchins, and sea cucumbers) appeared
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Ordovician Period: 485 – 444 million years ago
- Diversity of marine invertebrates, including mollusks, coelenterate, graptolites, trilobites, and Eurypterid.
- Earliest vertebrates (ostracoderms) appeared.
- First plants on land (Non – vascular plants like mosses and liverworts) emerged.
- A major extinction event wiped out 60% of marine species.
-
Silurian Period: 443 – 416 million years ago
- First developed jaw fish (Placoderm)
- First land plants evolved.
- First terrestrial arthropods appeared.
- Laurantia, Siberia, Baltica moved towards each other at the equator, forming the supercontinent, Euramerica.
- Glaciers melted, and the sea level rose due to a greenhouse effect.
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Devonian Period: 416 – 359 million years ago
- "Age of Fish" due to the abundance of fish diversity.
- First ferns on land appeared, along with tree-like plants.
- Abundance of marine life including bony fish.
- First seed-bearing plants evolved.
- First ammonite appeared.
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Carboniferous Period: 359 – 299 million years ago
- Forests and swamps with seed plants on land.
- Winged insects evolved.
- Early amphibians on land.
- Fish expanded in the oceans, with many mollusks and corals, but few trilobites.
- Inland seas reduced as continents collided to form Pangaea.
- Changes in glaciation and the formation of Pangaea led to land drying.
- Episodes of mountain building occurred.
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Permian Period: 299 - 252 million years ago
- Life in the oceans diminishes.
- First vertebrate herbivores on land appeared.
- Many gymnosperm plants emerged.
- 90% of marine species experienced extinction at the end of the period.
- Warming climate and dry interiors of continents.
Major Extinction Events and Ice Ages
- Late Ordovician
- Late Devonian
- Late Permian and early Triassic
- The Permian-Triassic extinction was the most devastating, destroying almost 90% of species and leaving only a few land species surviving.
Mesozoic Era Subdivisions
-
Triassic Period: 252 – 200 million years ago
- Rise of reptiles.
- First dinosaurs walked the land.
- Early mammals appeared.
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Jurassic Period: 200 – 145 million years ago
- Dinosaurs dominated the land.
- First birds evolved.
- Pangaea began to break apart.
- Formation of the Atlantic Ocean.
- First flowering plants (angiosperm) emerged.
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Cretaceous Period: 145– 66 million years ago
- Dominance of iconic dinosaurs such as Triceratops, Tyrannosaurus rex, and Pterosaurs.
- Angiosperm dominance.
- Marine reptile diversity.
- Mammalian diversification.
Cenozoic Era Subdivisions
- **Paleogene Period:** 66 – 23 million years ago
- **Neogene Period:** 23 – 2.6 million years ago
- **Quaternary Period:** 2.6 million years ago – present
Cenozoic Era
- "Age of Mammals"
- The extinction of many groups of giant mammals allowed smaller species to thrive and diversify because their predators no longer existed.
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Description
Explore the major divisions and subdivisions of the Geologic Time Scale. This quiz covers eons such as Precambrian and Phanerozoic, as well as significant events throughout Earth's history. Test your understanding of geological time periods and their characteristics.
