Flashcards: Geohistory


Atoms of the same element with different numbers of neutrons
Buried erosional surface
Time required for 50% of the atoms to decay
Oldest on bottom - Youngest on top
Sedimentary rocks are always deposited in horizontal layers
Two characteristics of an index fossil
Age of one thing (rock layer or fossil) compared to the age of another
Evidence of past life
What the divisions of geologic time (era, period, etc) are based on
What an unconformity always signifies
Age of the Earth
How absolute age is determined
Can only be used to date organic material
Only kind of rocks which contain fossils
Missing from Earth's original atmosphere
What landcape regions are based on
High elevations, steep slopes, tilted bedrock
High elevations, flat slopes, horizontal bedrock
Low elevation, flat slopes, horizintal bedrock
Factors that create landscape regions
Mountain building
Rounded features
Sharp, angular landscape features
Soils formed in place from the bedrock beneath them
Soils formed in one region but moved to a different location
All the rivers and streams that drain a given region
Method often used to find the absolute age of rocks
Along with index fossils, these serve as excellent time markers
Putting rock layers from widely separated areas into chronological order
This creates an exception to the Law of Superposition
Changes in life forms over time
Rapid evolution following a cataclysmic event such as an asteroid impact followed by long periods of slow, incremental change
Law of superposition
Law of original horizontality
1) Existed for a relatively brief period of geologic time 2) Wide geographic distribution
Relative dating
The fossil record (evidence of life on Earth)
Part of the rock record is missing
About 4.6 billion years
Radioactive dating methods
Carbon 14
> Elevation > Slope > Bedrock structure (tilting, folding, faulting)
Mountain landscape
Lowlands or plains
Uplift, erosion, climate, tilting, folding, faulting
Moist climate
Dry (arid) climate
Residual soils
Transported soils
Radioactive dating (using the half-life of radioactive isotopes in rocks)
Volcanic ash layers
Punctuated equilibrium