Ohio Geology Flashcards
What is the Law of Uniformitarianism?
Current geologic processes are the same as those in the past.
What is the Law of Superposition?
Unless the layers are deformed, a rock layer below is older than a rock layer above.
How can rock structures help determine the relative age of a rock layer?
Ripple mark crests point up. Sand dunes make curved lines towards the bottom of the layer. Graded bedding has larger particles on the bottom of the layer.
What is an unconformity?
A break in the rock record. Geologic evidence is missing.
How can erosion form an unconformity?
Erosion removes material and transports it to a different area.
How is the absolute age of a rock layer determined?
Radiometric dating uses the decay rates of radioactive elements to determine how much time has passed since deposition.
What is a fossil?
Fossils are the remains of once-living organisms.
How can fossils help determine the depositional environment?
Certain organisms live in a well-defined environment. Presence of those fossils indicate the environment where the organism lived and died.
What are five agents that can cause erosion?
Wind, flowing water, gravity, and animal movement.
What is the order of sediment size from smallest to largest?
Clay, silt, sand, gravel and boulders.
What is terrigenic sediment?
Rock particles that rivers carry from the land.
What is biogenic sediment?
The shells and bones of animals
What is limestone?
A sedimentary rock formed from calcium carbonate minerals.
What is sandstone?
A sedimentary rock formed from sand sized grains cemented together.
What is shale?
A sedimentary rock formed from clay particles cemented together.
What is a marine environment?
Marine refers to deposition that occurs in saltwater seas.
What is an aeolian environment?
Aeolian deposits refer to wind-carried sediment.
What is a lacustrine environment?
Lacustrine deposits occur in lakes.
What is a fluvial environment?
Fluvial environments refer to river deposits within the channel or into another body of water.
What is a geologic column?
A chart that shows different rock layers in an area.
How are fossils preserved by petrification?
Petrification is mineral replacement of the original material. Ex: petrified wood
How are fossils preserved by molds and casts?
When the organism dies, it can get buried in sediment and leave a cavity in the shape of the organism called a mold. Casts are made when the mold is filled with a mineral.
What are trace fossils?
Evidence such as footprints, burrows and coprolites that indicate a living organism was in the area.
What is an index fossil?
An organism that occurs only in rock layers of a particular age.
How can the lifespans of organisms help determine the age of a rock layer?
A rock layer’s age can only be an age that all fossils’ lifespans have in common.
What characteristics make a good index fossil?
A good index fossil has features that are easily recognized, distinguishable from similar organisms, and a short lifespan.
What is mutual bilateral symmetry?
A line dividing an organism into two equal parts (between valves)
What is independent bilateral symmetry?
A line dividing a section of an organism into two identical parts (within a valve)
What is a brachiopod?
A marine organism with an upper shell and lower shell attached to a stem
What is a trilobite?
An extinct marine organism with a carapace over the forepart and a segmented hind section divided into three lobes.
What are bryozoa?
A marine organism with branching colonies.
What are horn coral?
A marine organism with cone-shaped chambers in a colony.
When did the last series of ice ages cover Ohio?
During the Pleistocene epoch.
What is an ice age?
A period of extended low temperatures that cause large areas of the Earth to be covered with ice sheets.
What are the two types of glaciers?
Alpine glaciers and Continental glaciers
Which type of glacier is associated with ice ages?
Continental glaciers
What is a glacial groove?
A elongated channel preserved in rock that formed when heavy ice sheets with embedded boulders carved the bedrock as they passed.
Where in Ohio is a world-famous example of glacial grooves?
Kelleys Island in Lake Erie
By what two methods can glacial deposition occur?
Directly from retreating ice and carried by meltwater
Sediment deposited directly from retreating glaciers has what type of sorting?
Poorly sorted sediment with grain sizes ranging from boulders to clay.
Sediment deposited from meltwater has what type of sorting?
Well sorted sediment with grain sizes of sand and gravel.
How are glacial deposits in Ohio economically useful?
They can be used as construction materials or clay for pottery.
How do glacial deposits benefit Ohio’s water resources?
The Great Lakes formed from glacial activity during the last ice age. Glacial deposits in former stream and river channels form many current aquifers.
How did glaciers facilitate peat formation?
Dead plant material falls to the bottom of glacial lakes that do not provide the correct acidic and anaerobic conditions for full decay.
