Relative Dating of Rocks. Relative Dating and the Law of Superposition Relative dating is...
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Transcript of Relative Dating of Rocks. Relative Dating and the Law of Superposition Relative dating is...
Relative Dating of Rocks
Relative Dating and the Law of Superposition
Relative dating is determining the age of a rock or geologic event when comparing it to
other rocks or geologic events.
The Law of Superposition states that
“…in an area of undisturbed strata, the
bottom layer would be the oldest (since it was the first to form). Each layer above the bottom layer would be progressively younger. The top layer of exposed strata
would be the youngest (since it was the last to
form).”
Oldest layer of rock
Youngest layer of rock
Exceptions to the Law of Superposition
Much of the rock strata observed on Earth’s surface has been impacted by
the crustal dynamics of the Earth.
“How can a scientist determine the relative age of rock layers under these
conditions?”
Relative Dating of undisturbed rock? EASY!!!!!
Relative Dating of disturbed rock? MORE DIFFICULT!!!!!
Dating Rock Features
An igneous intrusion in younger than the rocks it
cuts through
An igneous extrusion in younger than the rocks it
cuts through
“A” is younger than B, C, and D
“D” is younger than E and F
Dating Rock Features
An inclusion is a portion of rock that is within an igneous
intrusion. For various reasons, the portion of rock did not melt and would be
older than the intrusion it is within.
The rock fragments with intrusion “M” are older than “M”.
The event of deformation of strata is younger than the strata
itself.
Layers Q, O, N. M and L were originally deposited as horizontal layers. These layers were then tilted. The tilting of the strata is younger than the formation of
the strata.
An unconformity is a buried weathered or
erosional surface. An unconformity is younger than the disturbed rock
layer. Layer J was deposited and lithified first. Layer J was weathered and/or
eroded (unconformity). Lastly, Layer K was deposited and lithified.
Relative Dating – Sample #1Determine the relative age of the rock and geologic events from the strata seen below.
Arrange the strata from youngest to oldest.
Relative Dating – Sample #2Determine the relative age of the rock and geologic events from the strata seen below. Arrange the strata from youngest to oldest.