break the rock into ions and use mass spectrometer to measure the number of parent isotopes and the number of daughter isotopes in the rock
Why are many rocks difficult to date?
The age of the rock must be so that we have enough parent and daughter atoms to measure; it cannot be told old or too young. It also must have the right minerals that contain the right amount of parent isotopes
The principle that states that geological processes causing change on the earth are gradual rather than catastrophic and are the same processes that can be observed today.
near-horizontal units that are internally composed of inclined layers; the original depositional layering is tilted, not as a result of post-depositional deformation
Sedimentary rock layers were originally horizontal when they were laid down and formed
Younger layers were originally on top of older layers
any rock that cuts across or penetrates a second rock body is younger than the rock it penetrates
Give examples of processes that deform rocks
Rock can be broken - faulted
bent - folded
liquid rock (magma) can push into (intrude) old rock
Why are names used for relative timing instead of numbers?
Numbers are only estimated
What is the geologic time scale measured in?
Millions of years
How old are the oldest rocks we've touched?
4.1 billion years old
How old is the earth?
4.6 billion years
How old are the oldest fossil cells?
3.5 billion years
How old is the blue ridge?
1.1 billion years
How old are the Appalachians?
3 billion years
How old are the first shells?
570 million years
How old are the first land plants?
400 million years
How old are dinosaurs?
65-250 million years
When did homo sapiens first exist?
0.5 million years ago
When was the end of the last ice age?
10 thousand years ago
What is catastrophism?
a belief that the earth's surface was generally a stable, nonchanging place that had remained quiescent except for violent upheavals during which mountains were thrust upward from the plains and canyons were formed as the earth's surface was ripped apart
What did the theory of neptunism involve?
the presence of a primordial ocean from which rocks at the earth's surface precipitated
What are beds?
Layers of rock that appear to be tilted or folded
What is the principle of original continuity?
accumulations of sediment are deposited in continuous sheets up to the point where they terminate against a solid surface
explains that the formation of igneous rocks by cooling from a hot, melted state rather than by precipitation from the ocean
the surface separating two rock sequences
the process of beds near the base of the sequences becoming compacted and beginning the transformation from sedimentation into sedimentary rocks
a molten liquid that can later cool to form an igneous rock
a rock that has been changed to such a great degree by heat and pressure but not to the point of melting