Fossils

Terms	Definitions
Fossil	The preserved remains or traces of living things
Cast	A fossil that is solid copy of an organism's shape, formed when minerals seep into a mold
Petrified Fossil	A fossil in which minerals replace all or part of an organism
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
Extinct	Describes a type of organism that no longer exists anywhere on Earth
Relative Age	The age of a rock compared to the ages of rock layers
Absolute Age	The age of a rock given as the number of years since the rock formed
Law of Superposition	The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layers above it and younger than the layer below it
Extrusion	An igneous rock layer formed when lava flows onto Earth's surface and hardens
Intrusion	An igneous rock layer formed when magma hardens beneath Earth's surface
Fault	A break or crack in Earth's lithosphere along which the rocks move
Unconformity	A place where an older, eroded rock surface is in contact with a newer rock layer
Index Fossil	Fossils of widely distributed organisms that lived during only one short period
Atom	The smallest particle of an element
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 Earth's history
How long ago did Earth form?	4.6 billion years ago
What is the first division of Earth's history called?	Precambrian Era
What force caused a ball of dust, rock, and ice to be pulled together to form Earth?	Gravity
List the 3 eras of Earth's history in order from oldest to youngest	Paleozoic Era Mesozoic Era Cenozoic Era
What percentage of a radioactive element remains after 2 half-lives?	25%
12.5% of a radioactive element remains. How many half-lives have passed?	3
Carbon-14 has a half-life of 5730 years. How many years will it be until 50% of the Carbon-14 remains?	5730 years
When carbon-14 undergoes radioactive decay, it turns into....	nitrogen-14
When potassium-40 undergoes radioactive dating, it turns into...	argon-40
If you find a fossil that is 4 billion years old, you should use what kind of radioactive dating?	potassium-argon dating
Rock A is older than Rock B but younger than Rock C. Is this an example of absolute age or relative age?	Relative Age
You find a rock that is 4380 years old. Is this an example of absolute age or relative age?	Absolute Age