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