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Transcript of Earth History
Chapter 12 A Tale of Two Ideas! *Archbishop James Ussher *
Calculated that Earth was formed on Sunday, October 23, 4004 BC.
Presented his ideas in a book called "Annals of the Old Testament, deduced from the first origins of the world" *
The prevailing thought was that the Earth was only about 5000 years old.
All major landforms were created by great catastrophes.
Known as... *
Catastrophism- The principle that states that all geologic change occurs suddenly.
Caused by rare, sudden events.
Mountains, Canyons and seas formed this way.
Occured over large areas.
(But then...) James Hutton *
Scottish geologist, physician, naturalist, chemist and experimental farmer.
Proposed that the Earth was much older.
Earth's landscape was constantly changing.
Earth's features formed slowly over time.
Known as... *
Uniformitarianism- The principle that states that the same geologic processes shaping the Earth today have been at work throughout Earth's history. Presented his theory in a paper called the "Theory of the Earth".
Published in the "Transactions of the Royal Society of Edinburgh" People really didn't catch on until 38 years later when... Charles Lyell *
British lawyer and the foremost geologist of his day
Published a series of books entitled "Principles of Geology"
Supported Hutton's uniformitarianism principal. Modern Geologists Believe in a hybrid of these two ideas called... *
Acutalism- Landforms are created by both gradual and uniform processes and catastrophies
Weathering and erosion.
Meteor strikes, volcanoes and earthquakes. *How do Modern Geologists know this? *
Relative Dating- Tells us the sequence in which events occurred, not how long ago they occurred.
5 ideas support this concept: *
1. Law of superposition
2. Principal of original horizontality.
3. Principle of Cross-Cutting Relationships.
4. Unconformities. *
Law of Superposition- In an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it. *
Principle of Original Horizontality- Layers of sediment are generally deposited in a horizontal position. Principle of Cross-Cutting Relationships- When a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, the fault or intrusion is younger than the rocks it affected. *
Inclusions- Pieces of one rock unit that are contained within another. The rock unit next to the one containing the inclusion must have been there first in order to provide the rock fragments. *
Unconformities- A surface that represents a break in the rock record, caused by erosion or lack of deposition. *
Siccar Point- a rocky outcrop in Eastern Scotland that
was the motivation for Huttons Ideas. *
Once we learn how to use relative dating to read the rocks we can then develop a geologic timescale using correlation.
Correlation- Establishing the equivalence of rocks of similar age in different areas.