The History of Life

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Geologic Time Noun

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[jee-uh-loj-ik tahym]

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Geologic Time

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The vast period of time covering Earth's history, which is estimated to be around 4.6 billion years old.

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Example: This chart shows Earth's history divided into eons, eras, periods, and epochs, highlighting major life forms and extinctions.

Front

Fossils Noun

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[fos-uhls]

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Fossils

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Evidence of ancient life, such as remnants, marks, or traces of life-forms that have been preserved in rock.

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Example: This image shows a fossilized skeleton in rock, demonstrating how fossils preserve evidence of ancient life.

Front

Body Fossils Noun

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[bod-ee fos-uhls]

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Body Fossils

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Fossils made from the preserved hard parts of an organism, such as its bones, teeth, or shells.

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Example: A fossil showing the preserved bones of an ancient animal, illustrating body fossils.

Front

Trace Fossils Noun

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[treys fos-uhls]

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Trace Fossils

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Fossils that preserve evidence of an organism's activities, such as tracks, burrows, impressions, or droppings.

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Example: A dinosaur footprint fossil shows evidence of the animal's movement, a type of trace fossil.

Front

Sedimentary Rock Noun

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[sed-uh-men-tuh-ree rok]

Back

Sedimentary Rock

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A type of rock formed from particles of gravel, sand, and mud that settle in layers and become compressed.

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Example: The image shows layers of sedimentary rock formed from particles settling in water.

Front

Relative Dating Noun

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[rel-uh-tiv dey-ting]

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Relative Dating

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A method used to determine if a rock layer or fossil is older or younger than another without finding its actual age.

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Example: Layers of sedimentary rock show which layers are older or younger, illustrating relative dating.

Front

Principle of Superposition Noun

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[prin-suh-puhl uhv soo-per-puh-zish-uhn]

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Principle of Superposition

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The scientific rule stating that in undisturbed rock layers, the lower layers are older than the layers above them.

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Example: The image shows layers of rock with the oldest at the bottom, teaching the Principle of Superposition.

Front

Absolute Dating Noun

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[ab-suh-loot dey-ting]

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Absolute Dating

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A method used to determine the specific age of a rock or fossil in years, often by measuring radioactive decay.

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Example: The graph shows how a substance decreases over time, helping to determine the age of rocks using absolute dating.

Front

Atom Noun

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[at-uhm]

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Atom

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The smallest particle of a chemical element that can exist, serving as the basic building block of all matter.

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Example: This image shows an oxygen atom, highlighting protons, neutrons, and electrons, which are the basic building blocks of matter.

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Isotope Noun

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[ahy-suh-tohp]

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Isotope

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A form of a chemical element with a different number of neutrons in its atom's nucleus than other forms.

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Example: The image shows an atom's nucleus with protons and neutrons, explaining isotopes as variations in neutron number.