Major Events in Earth's History

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Geologic Time Scale Noun

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[jee-uh-loj-ik tahym skeyl]

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Geologic Time Scale

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A timeline interpreted from rock and fossil records that organizes Earth's 4.6-billion-year-old history of change and evolution.

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Example: The image shows Earth's history with labeled eras and periods, highlighting major evolutionary events like the extinction of dinosaurs.

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Rock Strata Noun

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[rok strah-tuh]

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Rock Strata

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Layers of rock that provide evidence for the geologic time scale and the relative ages of fossils within them.

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Example: The image shows labeled rock layers in a canyon, helping explain how strata indicate Earth's history.

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Law of Superposition Noun

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[law uv soo-per-puh-zish-uhn]

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Law of Superposition

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The scientific law stating that in undisturbed rock layers, the oldest layers are on the bottom and youngest are on top.

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Example: The image shows rock layers with the oldest at the bottom and youngest at the top, illustrating the Law of Superposition.

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Index Fossil Noun

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[in-deks fos-uhl]

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Index Fossil

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A fossil of a widespread organism that existed for a short period, used to date and correlate rock layers.

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Example: The image shows index fossils in rock layers, helping to date and correlate layers.

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Mass Extinction Noun

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[mas ik-stingk-shuhn]

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Mass Extinction

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An event where many types of living things die out simultaneously, often marking boundaries between geologic eras.

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Example: An asteroid impact leads to mass extinction, marking a boundary between geologic eras.

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Pangaea Noun

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[pan-jee-uh]

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Pangaea

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The supercontinent, or single great landmass, that formed when all of Earth's continents moved together during the Paleozoic era.

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Example: The image shows Pangaea, the supercontinent, with labeled continents, explaining how Earth's landmasses were once joined.

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Invertebrate Noun

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[in-vur-tuh-brit]

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Invertebrate

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An animal that does not have a backbone or internal skeleton, representing the vast majority of animal species on Earth.

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Example: The image shows the anatomy of a jellyfish, highlighting its lack of a backbone, which is a key characteristic of invertebrates.

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Vertebrate Noun

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[vur-tuh-brit]

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Vertebrate

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An animal that has a backbone or spinal column, a group that includes fish, amphibians, reptiles, birds, and mammals.

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Example: This image shows examples of vertebrates, including fish, amphibians, reptiles, birds, and mammals, each labeled for easy identification.

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Amphibian Noun

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[am-fib-ee-uhn]

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Amphibian

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A cold-blooded vertebrate that lives part of its life on land and part of its life in water.

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Example: The image shows various amphibians like frogs and salamanders, illustrating their ability to live on land and in water.

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Reptile Noun

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[rep-tahyl]

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Reptile

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A vertebrate animal with scaly skin that lays amniote eggs with tough, leathery shells, allowing reproduction on land.

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Example: Illustrates different reptiles in a natural habitat, showing diversity but lacks detailed educational labels.