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Dating Methods Relative Dating

The document discusses the evolution of Earth and the methods used by geologists to date rocks and fossils, particularly through relative dating and the use of index fossils. Key principles such as the Principle of Superposition, Original Horizontality, and Cross-Cutting Relationships are outlined to help determine the relative ages of rock layers. The concept of unconformity is also introduced, highlighting gaps in the geological record due to erosion.

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42 views21 pages

Dating Methods Relative Dating

The document discusses the evolution of Earth and the methods used by geologists to date rocks and fossils, particularly through relative dating and the use of index fossils. Key principles such as the Principle of Superposition, Original Horizontality, and Cross-Cutting Relationships are outlined to help determine the relative ages of rock layers. The concept of unconformity is also introduced, highlighting gaps in the geological record due to erosion.

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sofiasumongsong
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JUAN SUMULONG MEMORIAL SCHOOLS SYSTEM INC.

Objective
✓To understand the evolution of
Earth, dating methods are used to
reconstruct the history of rocks,
minerals, and other materials
found on Earth.
Nicholas Steno (1638–1686), In the late 17th century
✓He introduced the geologic timescale by saying that each
layer of rock could represent a “slice” of time. Over the
course of time, many geologists used Steno’s principle,
and by the 19th century, Earth’s history was defined more
precisely.
✓Geologists agreed that if two strata found in distant
places have the same fossils, they could have been laid
down in the same geological time period.
✓Throughout the history of Earth, many
organisms have flourished and disappeared.
However, their remains or fossils were
preserved in some sedimentary rocks. The
presence of fossils helps geologists figure out
the date of rocks by means of correlation.
They use index fossils to establish geologic
timescales of a rock by matching the fossil
with the established period of its existence.
For example, using the index fossils shown in
Figure 2.37, if the fossils of trilobites were
found embedded in a certain layer of rocks,
there is a possibility that the rock existed
somewhere between 542 and 250 million Fig. 2.37Relative dating using index fossils
Source: http:/sciecelean.orgnz/CotextsDatin-the-ast/SienceIdeasand-C-
years ago. ncept/Relaive-dting
Relative Dating
✓ Relative dating is a method used to determine the relative
order of geologic events.
✓ This is done through stratigraphy (succession of rocks) where
the order of rock formations correlates to geologic time.
✓ The topmost layer suggests the most recent. In like manner,
the oldest rocks are understood to be at the bottom.
✓ This method does not provide actual numerical dates for the
rocks, but all are just estimates based on the profile of the
strata which includes chemical composition, rock type, and
presence of organisms.
Relative Dating
✓ is when you give the age of a rock or
fossil compared to another rock or fossil.

•Example: Rock A is OLDER than Rock B.


•An actual age in years is not determined.
Principle of
Superposition
A. Principle of Superposition:
When sedimentary rock layers are
deposited, younger layers are on top of older
deposits.
b. Principle of Original Horizontality:
Sedimentary rock layers are deposited horizontally.
If they are tilted, folded, or broken, it happened
later.
C. Principle of Cross-Cutting Relationships: If an
igneous intrusion or a fault cuts through existing rocks, the
intrusion/fault is YOUNGER than the rock it cuts through.
• Rock layers in different places and be correlated or
matched up by matching up the rocks and fossils in the
layers.
UNCONFORMITY
•When rock has been eroded, so you have
a missing section of time in the rock
record.

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