Age of the Earth

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What is the principle of original horizontality?
When sediments are deposited they form horizontal layers over time especially sedimentary rocks.
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What is the principle of superposition?
Where older rocks are beneath the younger rocks because new layers form from new deposited material over old layers.
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What is the term for assuming geological processes working today have been working throughout geological history?
Uniformitarianism
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What is a hiatus?
Where there is no layer for a specific time period in a rock. This layer must have been eroded away or there was a time of no-deposition before the next rock layer was added. - Indicates a time of different environmental conditions.
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What is the theory used to date rocks using fossils?
Principle of faunal succession
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What are index fossils?
Fossils of flora/fauna that existed for only a short interval of geological time. Presence in a rock can be diagnostic of a precise date for rocks in many locations.
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Are rocks cutting through others younger or older than their surroundings? How do we know this?
Younger- Principle of cross-cutting relations
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What is the principle of inclusion?
Rocks contained within another are older than their host. The younger rock must have formed around them.
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What uses the ratio of parent:daughter isomers?
Radiometric age. If we know the rate of decay for an isotope we can work out for how long a material has been decaying for and therefore the age of the rock.
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What is the oldest rock in the world?
Nuvvuagittuq Greenstone. 4.28 bn years old.
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What is the latest suggested age of the Earth?
4.57 billion years old.
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What is the difference between relative and numerical age?
Relative- specify age of one feature compared to another. Numerical- years (absolute age)
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What is the principle of baked contacts?
When igneous intrusions form, the heat from the intrusions "bakes" / metamorphoses surrounding rocks. The "baked" rocks must already have been present before
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Define:geochronology
The determination and interpretation of numerical ages of Earth material.
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What does Ka stand for?
1000's of years
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What does Ma represent?
Millions of years
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What can be used to describe billions of years?
Ga
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What are the three types of unconformity we have learned about in class?
Angular. nonconformity, disconformity
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What is discomformity?
\where there is a gap in the geological time record of the rocks. No new sediment was layed down for a period in time or erosion>deposiition.
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What could cause a disconformity to occur?
A drop in sea level may have exposed ancient lake or sea beds making them vulnerable to erosion. Subsequent sea level rise would allow new sediment layers to accumulate on top.
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Describe angular unconformity.
Where a rock layer is orientated differently to other rock layers beneath it, suggesting it is much younger than the other rocks having not been through the same tilting/folding etc.
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What is a noncomformity?
This is where intrusive igneous rock becomes exposed to weathering after the sediment above it is eroded away. The igneous rock becomes weathered before new layers of sediment accumulate on top possibly due to sea level rise.
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What is a stratigraphic formation?
An interval of strata composed of a specific rock type/s that can be traced over a fairly broad region.
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What is a geological contact?
The boundary surface between 2 formations. (Formation=products of deposition during a definable period of time).
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What are some issues using isotopic dating to determine the ages of rocks?
"Isotopic clock" only starts from when the rock crystals are cool enough for the isotopes to be locked in a lattice
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What is detrtital geochronology?
Determining the ages of the detrital/clastic grains in the rock to learn the age of the sediments's source region and where the sediments therefore must have come from.
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How does dendrochronology work?
Two new wood rings added each year. Darker more dense wood bands = produced end of Summer growing season- support and strength. In Spring: lighter less dense wood bands are grown to transport water to buds.
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How do the seasons affect sedimentation in lakes and seas?
Summer- tends to have more deposition- higher productivity=more organic matter. Winter=less deposition. Alternation between organic rich and poor bands.
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What happens to ice layers due to seasonal changes?
In dry periods e.g. summer- more dust. Winter snowy seasons=more snow. Alternation between clean and dusty ice layers.
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How do the seasons affect coral polyps and shell-growing organisms?
New shells are grown on a seasonal basis. Seasonal variations will produce ridges in the shells of mollusks and alternation in the light and dark bands in the heads of coral colonies.
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How might chemically precipitated rocks e.g Travertine show seasonal changes?
If precipitation and/or temperature varies seasonally distinct bands may appear in the sedimentary rock.
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What is magnetostratigraphy?
Using the knowledge that the Earth's magnetic field flips through geological time. You can compare the sequence of polarity reversals in a rock strata with a global reference column to determine its age.
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What is fission-track dating?
Decaying isotopes in crystals emit atomic particles which damage the crystals in a track. The larger the no. of fission tracks the older the crystal. Useful when you know the no. of tracks produced over time.
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Why did Kelvin calculate the inaccurate age of the Earth at 20 million years old?
He calculated how long it would take for the Earth to cool from a temperature as hot as the Sun but radioactivity produces new heat. Earth has been cooling for far longer than calculated.
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Card 2

Front

What is the principle of superposition?

Back

Where older rocks are beneath the younger rocks because new layers form from new deposited material over old layers.

Card 3

Front

What is the term for assuming geological processes working today have been working throughout geological history?

Back

Preview of the front of card 3

Card 4

Front

What is a hiatus?

Back

Preview of the front of card 4

Card 5

Front

What is the theory used to date rocks using fossils?

Back

Preview of the front of card 5
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