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How do we know what happened first?
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How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

Mar 30, 2015

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Page 1: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

How do we know what happened first?

Page 2: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

James Hutton (1726-1797) “Father of Modern Geology”

native of Edinburgh, Scotland educated as a medical doctor in Leiden (1749) passionate about scientific inquiry

Historical Developments

“Theory of the Earth” -- processes are slow; take a long time

Charles Lyell (1795-1875)• Scotsman who attended Oxford University • father was an avid naturalist • rebelled against prevailing thought of

“catastrophism”/”Neptunism”. “Principles of Geology” -- popularized Hutton’s views

idea of “uniformitarianism” -- same processes operating today occurred in the past

….the present is the key to the past….

Page 3: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

study of timing of geologic events and processes is geochronology

Relative timeorder of events or objects from first (oldest) to last (youngest)she is older than he is; she was born first and he was born last

age of events or objects expressed numericallyshe is twenty-one and he is nineteen

Absolute time

Page 4: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

Relative Time- “this rock is older than that”

Principles Used to Determine Relative Age Unconformities Correlation The Standard Geologic Time Scale Index Fossils

Absolute Time- “this rock is 28 million years old”

Principles of radioactive decay

Page 5: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

apply simple concepts to determine…

• original horizontality

• superposition

• lateral continuity

• cross-cutting relationships

• inclusions

• unconformities

Page 6: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

original horizontalityall beds originally deposited in water formed in horizontal layers

sediments will settleto bottomand blanketthe sea floor

Page 7: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

Superposition: within a sequence of undisturbed sedimentary or volcanic rocks, layers become younger, upward

Page 8: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

Lateral Continuity: original sedimentary layers extend laterally until it thins out at edges

rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.

Page 9: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.
Page 10: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

cross-cutting relationships

a disrupted pattern is older thanthe cause of the disruptione.g. an intrusion is youngerthan the rocks it intrudes

Page 11: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

inclusions

fragments of other rocks contained in a body of rockmust be older than the host rock

e.g. 1) xenoliths in granite are olderthan granite and2) pieces of rock inconglomerate are older than conglomerate

Page 12: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

unconformities

A gap in the geologic record -- “gap” may be an amount of time or amount of missing section

conformity

• relatively continuous deposition

• deposition of a sequence of parallel layers

• contacts between formations do not represent significant gaps in time

Page 13: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

from: http://www.elohi.com/photo/grandcanyon

conformity

Page 14: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

different types of unconformities

1. angular unconformity

• contact separates overlying younger layers from tilted older layers• sequence of layers is not parallel

• contacts between formations may represent significant amounts of time

angular unconformity

Page 15: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

angular unconformityfrom: http://www.uakron.edu/envstudies/parks/rmgcan2.html

Page 16: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

angular unconformity

Page 17: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

different types of unconformities

2. disconformity

• contact separates beds (formations) that are parallel

• sequence of layers is parallel

• contacts between formations may represent significant amounts of time• missing time is difficult to recognize

Page 18: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

different types of unconformities

3. nonconformity

• strata deposited on older crystalline (metamorphic/igneous) rock• erosion surface on igneous/metamorphic rock covered bysedimentary rocks

• large gap in geologic record

nonconformity

Page 19: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

Unconformity Types Using Grand Canyon as Example

Page 20: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.
Page 21: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.

faunal succession (correlation by fossils)

How is this done?

index fossil short-lived organism; points to narrow range of geologic time

fossil species succeed one another through the layers in a predictable order

fossil assemblage group of fossilsassociatedtogether

Page 22: How do we know what happened first?. James Hutton (1726-1797) Father of Modern Geology native of Edinburgh, Scotland educated as a medical doctor in Leiden.