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 division of geologic time is 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

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.

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Isotope

Unconformity

Half life

Law of superposition

Law of original horizontality

1) Existed for a relatively brief time 2) Wide geographic distribution

Relative age

Fossil

Past life on Earth

Part of the geologic record is missing

4.6 billion years

Radioactive dating

Carbon 14

Sedimentary

Oxygen

Elevation, slope and bedrock structure

Mountains

Plateaus

Plains (Lowlands)

Uplift, erosion, climate

Orogeny

Humid (wet) climate

Dry (arid) climate

Residual soils

Watershed

Uranium-lead dating

Volcanic ash layers

Correlation

Overturning

Evolution

Punctuated equlibrium

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Flashcards: Geologic History & Landscapes