Flashcards in Geologic Time Deck (17):
how is relative dating different from absolute dating?
relative dating places events in sequential order of their occurrence.
absolute dating gives an actual date
State the law of superposition
sediments are deposited in horizontal layers.
in undisturbed sedimentary strata the oldest rock is on the bottom
What is the principle of uniformitarianism?
geologic processes today are the same as they were in the past
What does the law of crosscutting say?
intrusions and faults are younger than the rock they intrude into
Which is older, a conglomerate or the pebbles that are ound in the conglomerate?
the pebbles found in the conglomerate
a buried erosional surface between rock layers that would not normally touch indicating- a missing section of rock history
What is a fossil?
any evidence of past life preserved in rock (Ice or amber)
List the 6 ways that fossils form
What is an index fossil used for? What are the 4 criteria for an index fossil?
indx fossils are used to help in the relative dating or rock layers. 4 criteria are easy to recognize, abundant, and short lived ,, and widespread (specific time/rock)
How is a radioactive isotope used to determine absolute age?
by using the percentage (or ratio) of parent and daughter material to calculate half lifes and then age
What is a half-life?
the time required for a radioactive isotope to decay by 50%, resulting in half the parent material atoms
What is the decay product and the half life for the isotope Carbon-14
What is the decay product and half life for the isotope uranium 238
4.5 billion years
What is the decay product and half life for the isotope rubidium 87
what is the decay product and half life for the isotope potassium 40
What isotope is used to find the age of organic remains