地质中的时间尺度
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Paleontology is the study of ancient life from fossilized remains.
William Smith in the 19th century was an engineer who noted that similar rocks in different areas had similar fossils and that different rock types had different fossils.
There are limitations for using stratigraphy
to keep time because,
(1) sedimentation rates are variable
e.g. Mississippi can deposit 1m of sediment in 1000 y
(aka “the field of stratigraphy”)
Principle of Original Horizontality
sediments deposited innearly flat layers. Crossbedded layers are contained within overall flat beds.
Concepts you will need to know for the exams CHAPTER 8
Geologic Time Scale Relative age Absolute age
Principle of original horizontality Principle of superposition
Principle of cross-cutting relationahips Unconformity
Angቤተ መጻሕፍቲ ባይዱlar unconformity Disconformity Half-life
Geologic Time Scale
Geologists differ from other professional scientists in their view of time.
If layers are faulted (broken) or folded it means that they were deformed AFTER sediments were deposited.
Principle of Superposition Lowest layers are older If this is not so, then the layers have been overturned by tectonic activity:
Geologists deal with periods of time that go as far back as the origin of the universe.
Before we had the ability to read the “atomic clocks” of nature, geologists used the concept of relative ages.
He made a composite (ideal, pieced-together) stratigraphic succession as in the following figure
Most of geologic time goes unrecorded Sometimes NO SEDIMENT is DEPOSITED over an interval of time (hiatus)
Other times sediment is eroded away.
This is happening here: Mississippi Valley is filling whereas the higher ground is being eroded away.
An unconformity in which the layers above an erosional surface are parallel to the layers below is known as a DISCONFORMITY
With the advent of atomic/radioactive decay techniques we began to obtain absolute dates.
Absolute dates or ages have specific numbers
Relative dating has been done in the past through the study of layers of sedimentary rock
The deep ocean may deposit 1mm / 1000 years
We need to estimate time in another way and be able to recognize when the representation of time via sediments is incomplete.
John Grotzinger, Thomas H. Jordan Frank Press and Raymond Siever
Understanding Earth
Fifth Edition
Chapter 8: The Rock Record and the
Geologic Time Scale
Copyright © 2007 by W. H. Freeman & Company
We can see changes in the landscape over time.
We can see one type of organism replace another type of organism through the fossilized remains of these changes over time.
William Smith in the 19th century was an engineer who noted that similar rocks in different areas had similar fossils and that different rock types had different fossils.
There are limitations for using stratigraphy
to keep time because,
(1) sedimentation rates are variable
e.g. Mississippi can deposit 1m of sediment in 1000 y
(aka “the field of stratigraphy”)
Principle of Original Horizontality
sediments deposited innearly flat layers. Crossbedded layers are contained within overall flat beds.
Concepts you will need to know for the exams CHAPTER 8
Geologic Time Scale Relative age Absolute age
Principle of original horizontality Principle of superposition
Principle of cross-cutting relationahips Unconformity
Angቤተ መጻሕፍቲ ባይዱlar unconformity Disconformity Half-life
Geologic Time Scale
Geologists differ from other professional scientists in their view of time.
If layers are faulted (broken) or folded it means that they were deformed AFTER sediments were deposited.
Principle of Superposition Lowest layers are older If this is not so, then the layers have been overturned by tectonic activity:
Geologists deal with periods of time that go as far back as the origin of the universe.
Before we had the ability to read the “atomic clocks” of nature, geologists used the concept of relative ages.
He made a composite (ideal, pieced-together) stratigraphic succession as in the following figure
Most of geologic time goes unrecorded Sometimes NO SEDIMENT is DEPOSITED over an interval of time (hiatus)
Other times sediment is eroded away.
This is happening here: Mississippi Valley is filling whereas the higher ground is being eroded away.
An unconformity in which the layers above an erosional surface are parallel to the layers below is known as a DISCONFORMITY
With the advent of atomic/radioactive decay techniques we began to obtain absolute dates.
Absolute dates or ages have specific numbers
Relative dating has been done in the past through the study of layers of sedimentary rock
The deep ocean may deposit 1mm / 1000 years
We need to estimate time in another way and be able to recognize when the representation of time via sediments is incomplete.
John Grotzinger, Thomas H. Jordan Frank Press and Raymond Siever
Understanding Earth
Fifth Edition
Chapter 8: The Rock Record and the
Geologic Time Scale
Copyright © 2007 by W. H. Freeman & Company
We can see changes in the landscape over time.
We can see one type of organism replace another type of organism through the fossilized remains of these changes over time.