Earth History

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Unit 5 Grade 9 Earth Science

stromatolites

are rocks made from millions of microscopic layers comprised of the remains of bacteria. They dominated the Earth for over 2 billion years and without the oxyegen they produced, we may not have evolved. They can still be seen in in Shark Bay, Australia.

Catastrophism

the school of the thought that believes singular,random and unpredictable events have been most responsible for the course of history

uniformitarianism

the idea that the same explainable and predictable geologic activity that takes place on the Earth today has been more instrumental in shaping our planet since its creation.

geologic time

a chronological record of the significant geologic events, life and continental positions on the Earth since its creation. The timeline is based upon fossil evidence and the rock record.

fossils

any evidence of prehistoric life, ie. Bones,footprints, molds,casts, etc.

index fossils (regents!)

a fossils that is a good geologic time marker (!!) (1)It existed over a short period of time (2) over a broad are, and has (3) easiliy recognizable volcanic ash has the same properties as an index fossil

the rock record

evidence of past geologic events that occurred in a given area derived from study of the type and size of rock layer formed throughout history. gaps are present due the weathering and erosion

orogeny

time of mountain building/formation

evolution

change,diversification, or adaption of a species to its environment over time (life started in the oceans)

extinctions

when a species ceases to exist

relative age

how old something is with respect to its surrondings

originial horizontality

the principal that sedimentary rocks layers are initially deposited in flat layers(usually under water) one on top of another. if they do not appear as such, some geologic activity has changed their position

supersition

the understanding that the rock layers on top of a sequence of stratum is the youngest whereas the layer on the bottom is the oldest(unless "overturning has occurred)

overturning

intense folding of rock layers that results in the older strata being pushed on top of the younger layers

1. Deposition and Compaction

this step is always added when a sedimentary rock layer is present

2. Intrusions/Extrusions

this step is used to explain the presence of igneous rock. Always accompanied by CONTACT METAMORPHISM extrusions won't show contact metamorphism on the layer's top

3. Folding/tilting

when whole layers are bent, curved or tilted by tectonics

4. Faulting

when layers are cut or displaced as a result of an earthquake

5. Metamorphism

mentioned when a metamorphic rock layer is present, usually found at the bottom of sequences or next to intrusions/extrusions

6. Weathering and Erosion

when some of a rock layer is missing or has been erased. sometimes shown as a layer with a wavy top

unconformity (regents!)

a buried erosional surface formed from compaction of sediments, weathering, and erosion, and then additional deposition and compaction

emergence

when a landscape uplifts above the water MUST OCCUR for WEATHERING AND EROSION to take place

submergence

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