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U6 Geological time


Amber Fossilized tree sap.
Absolute Age The actual age of a material in years.
Fossil Any remains or trace of an ancient organism.
Cast A mold filled with sediment and hardened to create a replica of the original fossil.
Cross-cutting relationships One of Steno’s principles that states that an intrusion or fault is younger than the rocks that it cuts through.
Index Fossil A fossil indicates the relative age of the rock in which it is found. Index fossils come from species that were widespread but existed for a relatively brief period of time.
Ice Core Cylinder of ice extracted from a glacier or ice sheet.
Isotope A chemical element that has a different number of neutrons.
Mold An impression made in sediments by the hard parts of an organism.
Permineralization Fossilization in which minerals in water deposit into empty spaces in an organism.
Pangaea Pangaea is a hypothetical supercontinent that included all current land masses, believed to have been in existence before the continents broke apart during the Triassic and Jurassic Periods.
Trace Fossil Evidence of the activity of an ancient organism; e.g. tracks, tubes, and bite marks.
Geologic Time the succession of eras, periods, and epochs as considered in historical geology.
Lateral Continuity A sedimentary rock layer that extends sideways as wide as the basin in which it forms.
Original Horizontality Sedimentary layers that were deposited horizontally.
Outgassing The transfer of gases from Earth’s mantle to the atmosphere by volcanic eruptions.
Orogeny A mountain building event, usually taking place over tens or hundreds of millions of years.
Relative Age The age of an object in comparison with the age of other objects.
Radiometric dating Process of using the concentrations of radioactive substances and daughter products to estimate the age of a material.
Superposition In a sequence of sedimentary rock layers, the oldest is at the bottom and the youngest is at the top.
Supercontinent A collection of continents that have come together because of the plate tectonics processes.
Unconformity A gap between rocks of very different ages. Unconformities are often marked by an erosional surface.
Uniformitarianism Natural processes operated the same way throughout Earth’s history as they do today.
Half-Life The amount of time required for half of the atoms of a radioactive substance to decay to the daughter product.
Differentiation The separation of planetary materials by density to create distinctly different layers.
evolution Change through time. The change in the genetic makeup of a population of organisms over time such that a new species is often the result.
Natural Selection The mechanism for evolution. Natural processes favor some traits over others in a population causing those traits to be more common in subsequent generations. This results in change to a new species or subspecies.
Created by: _i.c.a_