The Rock Record/Precambrian Earth Flashcards
Eon
-The longest unit of time
-measured in billions
Era
-second longest unit of time
-measured in tens of millions of years
Period
-second shortest unit of time
-measured in millions of years
Original Horizontally
-Sedimentary rocks are deposited in horizontal or nearly horizontal layers.
Superposition
-In an undisturbed rock sequence, the oldest rocks are at the bottom and each consecutive layer is younger than the layer beneath it.
Absolute Age Datin
-Method for determining the actual age of a rock
Radioactive Decay
-the emission of radioactive particles
-resulting in changing bingo other isotopes over time
Half-Life
-the time required for one half of the parent isotope decaying into a daughter
Index Fossil
-fossils that are easily recognizable
-spread out
Original Preservation
-The remains of plants and animals that have been altered very little since the organism’s death
Mineral Replacement
-The process whereby a buried organism’s hard parts are replaced with minerals, usually carried in groundwater
Mold
-impression left in place of a decomposed organism
Cast
-a filled in mold that preserves original shape of the organism
Trace
-Indirect evidence of past organisms including worm trails, footprints, and tunneling burrows
Earths Early Heat Sources
-gravitational
-radioactivity
-bombardment from meteorites
