Geologic History Test Flashcards
Principle of Superposition
Oldest layers are at the bottom, youngest at the top.
Olderlayers on the bottom, younger layers on top
Original Horizontality
Sediments are deposited in horizontal layers parallel to the earth’s surface.
Law of Crosscutting Relationships
Anything that cuts across layers (fault, folding, tilting, intrusion, extrusion) must be younger than the layers it cuts across.
Unconformity
a buried erosional surface. Look for “wavy” or irregular lines that have layers on top of them. Formed as a result of erosion and deposition
Contact Metamorphism
Indicated by small black lines. Tells you if the igneous rock is an intrusion or an extrusion based on which surrounding rocks have contact metamorphism.
The letter for each fossil can be found in the _____________________________.
This tells you which geologic ______/______ the organism lived in
Time Distribution of Fossils column on page 9.
period/era
There are different ___________ of fossils (ex: trilobites) that can have more than one index fossil in them. Follow the ______ _________ _________ on page 9. When the gray line ends, that means the organism went _______
categories
vertical gray lines
extinct
Index fossil characteristics
Found over a widespread area and lived for a relatively short period of time (found in only one layer)
You may sometimes have to go to page _ of the ESRT to determine areas of NY that fossils can be found in.
3
Absolute dating is finding
the numerical age of something. Ex: 100 million years
Relative dating is
comparing the ages of two or more layers. Ex: Layer A is older than Layer B.
Some Elements are Radioactive. This means that they emit ________ through the process of __________.
particles
radiation
Radioactive elements are sometimes called
isotopes
Radioactive elements decay (lose particles) at ________ rates.
predictable
They decay into their ________/__________ _________.
daughter elements/isotopes.
The time it takes for half the amount of a given element to decay is called a ______-_______
half-life
During each half-life, half of the _________ __________ will decay to its __________ ___________ __________.
radioactive (parent) element
stable (daughter) decay product
If we know how much of the parent isotope is left in a rock sample, then we can figure out ____ ____ _____ _____ _____ ______
how long it has been around
Carbon 14 - Can ONLY be used to date _____ _______ _______ _______ _______ _________ __________ ________
once living fossils from the past 50,000 years.
Wood, pollen, bone, cotton, etc
Holocene and Late Pleistocene epochs ONLY
We use the Half-Life of a radioactive isotope to determine the ________ _______ of rocks and fossils.
numerical ages
Half-life is the time it takes for ______ of a sample to decay.
half (50%)
Glaciers ______/_______ due to the force of _______
move/advance
gravity
Glaciers form when _____ falls in winter and does not _______ _______/______ during the summer months.
snow
completely melt/retreat
Drumlins are…
oblong hills created by glaciers and tell us the direction of ice flow (they are fatter in the direction the ice came from)
Striations
Scratches or grooves in bedrock that form when a glacier carrying rocks moves over the bedrock.
Other glacial landforms include:
eskers, moraines, kame, till, kettle lakes, grooves, polish, U shaped valleys
Glacial feature that consists of unsorted/unlayered sediments
Till
Glaciers cause _ shaped valleys
U
Meltwater (running water from a melting glacier):
Sorted and layered deposits (just like rivers/streams)
Forms eskers, kames, outwash plain
