| Question |
Answer |
| fossil |
evidence or remains of once-living plants or animals |
| unaltered hard part |
a bone or shell that has not undergone change since the organism's death |
| altered hard part |
organic material is replaced with minerals |
| petrified |
turned to stone |
| mold |
impression left by an organism - a leaf or shell for example |
| cast |
mold is filled with minerals |
| index fossil |
used to correlate rock layers; easily recognized, abundant, and widespread geographically |
| trace fossil |
indirect evidence of life, like a footprint |
| stratigraphy |
the study of rock layers and the fossils they contain |
| uniformitarianism |
forces and processes that we observe today have been at work for a very long time |
| original horizontality |
sediments are laid down in horizontal layers |
| superposition |
in undisturbed bedrock, the oldest rocks are at the bottom and the youngest rocks are on the top |
| cross-cutting relationship |
intrusion, folding, or fault is younger than the rock it cuts across |
| unconformity |
buried surface of erosion |
| relative age |
puts the age of materials in order; puts events in a sequence |
| absolute age |
gives the actual age of a material |
| isotope |
atom that has a different number of neutrons in its nucleus than normal |
| half life |
the amount of time it takes for half the parent material to decay to daughter material |
| parent material |
the original, unstable isotope |
| daughter material |
the stable isotope that results from radioactive decay |
| radioactive decay |
spontaneous breakdown of nuclei of unstable isotopes |
| radiometric dating |
using the process of radioactive decay to find the absolute date of a material |
| radiocarbon dating |
finding the absolute age of a once-living organism using the carbon 14 decay process |
| dendrochronology |
tree ring dating |
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