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Earth Science - A Trip Through Geologic Time

Chapter 9 - A Trip Through Geologic Time

FOSSILThe preserved remains or traces of living things.
PALEONTOLOGISTA scientist who studies fossils to learn about organisms that lived long ago.
SEDIMENTARY ROCKA type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together.
PETRIFIED FOSSILA fossil in which minerals replace all or part of an organism.
MOLDA fossil formed when an organism buried in sediment dissolves, leaving a hollow area.
CASTA fossil that is a copy of an organism’s shape formed when minerals seep into a mold.
CARBON FILMA type of fossil consisting of an extremely thin coating of carbon on rock.
TRACE FOSSILA type of fossil that provides evidence of the activity of ancient organisms.
SCIENTIFIC THEORYA well-tested concept that explains a wide range of observations.
EVOLUTIONThe process by which all the different kinds of living things have changed over time.
EXTINCTDescribes a type of organism that no longer exists anywhere on Earth.
RELATIVE AGEThe age of a rock compared to the ages of rock layers.
ABSOLUTE AGEThe age of a rock given as the number of years since the rock formed.
LAW OF SUPERPOSITIONThe geologic principle that states that: In horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.
UNCONFORMITYA place where an old, eroded rock surface is in contact with a newer rock layer.
FAULTA break or crack in Earth’s lithosphere along which the rock moves.
INTRUSIONAn igneous rock layer formed when magma hardens beneath Earth’s surface.
EXTRUSIONAn igneous rock layer formed when lava flows onto Earth’s surface and hardens.
INDEX FOSSILFossils of widely distributed organisms that lived during only one short period.
ATOMThe smallest unit of an element that retains the properties of that element.
ELEMENTA substance composed of a single kind of atom.
RADIOACTIVE DECAYThe breakdown of a radioactive element, releasing particles and energy.
HALF-LIFEThe time it takes for half of the atoms of a radioactive element to decay.
GEOLOGIC TIME SCALEA record of the geologic events and life forms in Earth’s history.
ERAOne of the three long units of geologic time between the Precambrian and the present.
INVERTEBRATEAn animal without a backbone.
PERIODOne of the units of geologic time into which geologists divide eras.
EPOCHSubdivisions of the periods of the geologic time scale.
VERTEBRATEAn animal with a backbone.
AMPHIBIANA vertebrate that lives part of its life on land and part of its life in water.
REPTILEA vertebrate with scaly skin that lays eggs with tough, leathery shells.
MASS EXTINCTIONWhen many types of living things become extinct at the same time.
MAMMALA warm-blooded vertebrate that feeds its young milk.

Middle school science teacher
Hedgesville Middle School

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