Earth History Exam 5 Study Guide: Limestone & Past Environments
1. Sedimentary Rock Characteristics:
Rock
Texture
Color
Acid Test
Rough
Tan to brown,
color varies
No fizz
Smooth
Dark grey
No fizz
Plant fossil
evidence
Rough
Light colors
Fizz
shells
Sandstone
Shale
Other
Observations
Layered,
crossbedding
Limestone
2. Sedimentary Rock Formation Environments
Rock
Sandstone
Environment
Desert dune, beach,
mountain stream
Marsh/Swamp
Evidence
Crossbedding, sand particles with wind frosting,
beach particles have rounded edges, mountain
stream sand is angular
Plant/fern fossils, clay/silt particles
Ocean
Shells, calcite
Shale
Limestone
3. Explain the Principle of Superposition and how it relates to rock layers.
The principle of superposition states that rock layers on the bottom of a rock column are
older that the rock layers on top. Youngest layers are on the top.
4. Why does limestone fizz when hydrochloric acid is placed on it?
a. What mineral is present that reacts with the HCl acid?
Calcite (a form of calcium carbonate)
b. Explain the chemical reaction that occurs to cause the fizzing.
The HCl reacts with the calcite to create carbon dioxide bubbles (the fizzing)
5. What are two ways that calcium carbonate can form in an ocean environment?
a. The calcium in the bones, shells, and scales of dead animals combines with
carbon and oxygen.
b. The carbon dioxide (CO2) exhaled by organisms reacts with calcium in the
water.
6. Explain the process of limestone formation.
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Calcium carbonate does not dissolve in water, so if it forms in the sea or falls into
the sea, it will sink to the bottom.
The calcium carbonate acts as a matrix and forms a layer at the bottom of the
ocean.
Over time through compaction the layer turns into limestone.
7. What is a fossil?
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A fossil is any remains, trace, or imprint of a plant or animal that has been
preserved in the earth’s crust since some past geological or prehistoric time.
Any evidence of past life