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The Rock and Fossil Record

Across
The death of every member of a species
A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time
Any method of measuring the age of an event or object in years
A principle that states that geologic processes that occurred in the past can be explained by current geologic processes
A method of determining the age of an object by estimating the relative percentages of a radioactive isotope and a stable isotope
A fossilized mark that is formed in a soft sediment by the movement of an animal
A mark or cavity made in a sedimentary surface by a shell or other body
A principle that states that younger rocks lie above older rock if the layers have not been disturbed
The time needed for half of a sample of a radioactive substance to undergo radioactive decay
The scientific study of fossils
A type of fossil that forms when sediments fill in the cavity left by a decomposed organism
A principle that states that geologic change occurs suddenly
A unit of geologic time into which eras are divided
Down
An atom that had tghe same number of protons as other atoms of the same element do but that had a different number or neutrons
The largest division of geologic time
A unit or geologic time that includes two or more periods
The process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element
A fossil that is found in the rock layers of only one geologic age and that is used to establish the age of the rock layers
The remains or physical evidence of an organism preserved by geological process
A subdivision of a geologic period