Fossil Sedimentary Rock Mold Cast Petrified Fossil A trace of an ancient organism that has been preserved in rock Sedimentary Rock A type of rock that forms when particles form other rocks or the remains of plants and animals are pressed and cemented together Mold A fossil formed when an organism buried in sediment dissolves leaving a hollow area Cast A fossil that is a copy of the organism’s shape formed when minerals seep into the mold Petrified Fossil A fossil in which minerals replace all or part of the organism

A well tested concept that explains a wide range of observations Carbon Film A type of fossil consisting of an extremely thin coating of carbon on rock Trace Fossil A type of fossil that provides evidence of the activities of ancient organisms Paleontologist A scientist who studies fossils to learn about organisms that lived long ago Scientific Theory A well tested concept that explains a wide range of observations Evolution The process by which all the different kinds of living things have changed over time

Extinct Relative Age Absolute Age Law of Superposition Extrusion Describes a type of organism that no longer exists on the Earth Relative Age The age of a rock compared to the ages of rock layers Absolute Age The age of a rock given as a number of years since that rock formed Law of Superposition The geologic principle that states that in horizontal layers of sedimentary rock each layer is older than the one above it and younger than the one below Extrusion An Igneous rock layer formed when lava flows onto the Earth’s surface and hardens

Intrusion Fault Unconformity Index Fossil Atom An igneous layer formed when magma hardens beneath the Earth’s surface Fault A break or crack in Earth’s lithosphere along which rocks can move Unconformity A place where an old eroded rock surface is in contact with a newer rock layer Index Fossil Fossils of widely dispersed organisms that lived during only one short period Atom The smallest particle of an element

Element Radioactive Decay Half Life Geologic Time Scale Era A substance in which all the atoms are the same and cannot be broken down into other substances Radioactive Decay The breakdown of a radioactive element releasing particles and energy Half Life The time it takes for half of the atoms of a radioactive element to decay Geologic Time Scale A record of the geologic events and life forms in the Earth’s history Era One of the three long units of geologic time between the Precambrian and Present

Period Comet Continental Drift Invertebrate Vertebrate One of the units of geologic time into which geologists divide eras Comet A loose collection of ice, dust and small rocky particles typically with a long narrow orbit of the Sun Continental Drift The hypothesis that the continents slowly move across Earth’s surface Invertebrate An animal without a backbone Vertebrate An animal with a backbone

Amphibian Reptile Mass Extinction Mammal A vertebrate that lives part of its life on land and part of its life in water Reptile A vertebrate with scaly skin that lays eggs with tough leathery shells Mass Extinction When many types of living things become extinct at the same time Mammal A warm blooded vertebrate that feeds its young milk