extinction – n. the state or situation that results when something (such as a plant or animal species) has died out completely

sediment – n. tiny pieces of rock and other material that settle at the bottom of the ocean

ratio – n. the relationship that exists between the size, number, or amount of two things and that is often represented by two numbers

food chain – n. a series of living things in which each one uses the next lower member of the series as a source of food

vacate ­­– v. to leave empty or open
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