Geology 101 Quiz 9 Flashcards
two types of age determination
relative and absolute dating
relative dating
finding the age relative to another object or event (younger or older)
absolute dating
finding the age in years
absolute dating has only been possible since the discovery of ? at the start of the ? century
radioactivity; 20th
principle of original horizontality
sedimentary layers, called strata, were deposited nearly horizontally
principle of superposition
younger sediments are deposited on top of older sediments
in undisturbed strata, the ? layer will always be the youngest
upper
the order of the layers repeats itself
thrust fault
when a fold has been pushed over onto itself - strata repeat, but in the middle of the repeating layers, an additional repeated set is upside down
overturned fold
principle of original lateral continuity
identical layers on opposite sides of a valley were once continuous
principle of inclusions
if a rock contains fragments of rock from an adjacent unit, the adjacent unit must be older
principle of cross-cutting relationships
younger rock or features cut across older rocks or features
uncomformity
an eroded surface
index fossil
a fossil organism with widespread distribution that existed for a short time span
use of index fossils
only organisms that are widespread and with a relatively short time of existence are useful for relative dating