b geologic time.ppt

7/28/2019 b Geologic Time.ppt

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Timeand distance

Moon:

Mars:

Sun:

Pluto:

212,000 miles

48,000,000 miles

93,000,000 miles

3.6 billion miles


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Milky Way Galaxy

> 100 billion suns

60,000 light years

wide

Earth

Nearest star?

Alpha Centauri:

4.3 light years or

25 trillion miles


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Hubble telescope estimates >125 billion galaxies

Nearest?Andromeda

2 million

light years away

For every grain of sand

on Earth, there are a

million stars.


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Geologic Time Scale


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How do you determine ages?

1. Relative age dating. Comparing the age of one thing relativeto something else.

2. Absolute age dating. Using analytical techniques to determine

the real age of an object.


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Superposition

Sediments accumulating on top are younger than

those below.


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Cross-Cutting

Rocks which cross-cut are younger than those they cut.


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Unconformity

Sediment deposition, followed by a period of eroison,

then more sediment deposition. End result? A time gap.


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Grand Canyon


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Index Fossils

Organisms which lived only during a specific period

of time.


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Correlation

Same rock layers, correlated over vast distances

Same rock types, ages, fossils, etc.


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Correlation was used during the development of the

continental drift theory, years ago.


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Absolute Age Dating

Relative age dating placed rock layers into

a specific order.

Radiometic age dates were used to determine

the age of the rock layers and verify the

ordering.


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The AtomAtom: In the nucleus, there are protons (+) and neutrons (neutral charge)

Surrounding the nucleus are negatively charged electrons

- used for bonding with other atoms to form molecules

Atomic number = number of protons in the nucleus

Atomic weight = # protons + # neutrons

Isotope: Same number of protons, different number of neutrons


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Radioactivity

Some isotopes are unstable. These will decay to stable isotopes called

daughter products.

As isotopes decay, they give off subatomic particles + heat

Radiation


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To build a nuclear reactor, what you need is some mildly enriched uranium. Typically, the uranium is formed into pellets with

approximately the same diameter as a dime and a length of an inch or so. The pellets are arranged into long rods, and the rods are

collected together into bundles. The bundles are then typically submerged in water inside a pressure vessel. The water acts as acoolant. In order for the reactor to work, the bundle, submerged in water, must be slightly supercritical. That would mean that, left to

its own devices, the uranium would eventually overheat and melt.

To prevent this, control rods made of a material that absorbs neutrons are inserted into the bundle using a mechanism that can

raise or lower the control rods. Raising and lowering the control rods allow operators to control the rate of the nuclear reaction.

When an operator wants the uranium core to produce more heat, the rods are raised out of the uranium bundle. To create less

heat, the rods are lowered into the uranium bundle. The rods can also be lowered completely into the uranium bundle to shut the

reactor down in the case of an accident or to change the fuel.


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Nuclear Meltdown

Chernobyl, Ukraine: 1986

Explosion released 200 times more radiation than the

Hiroshima and Nagasaki bombs combined.


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Contaminated Areas


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Sarcophagus


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Unstableisotope

Stable daughter

product


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Half life: Over a given period of time, half the parent isotope

decays into its daughter product.


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Examples

Uranium 238 to Lead 206: 4.5 billion years

Uranium 235 to Lead 207: 713 million years

Thorium 232 to Lead 208: 13.9 billion yearsRubidium 87 to Strontium 87: 50 billion years

Potassium 40 to Argon 40: 1.5 billion years


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Zircon

Common in granites

Zr+Si+O

Trace amounts of Th & U

Link to radon

Radium->Radon->PoluniumRadon half life: 3.8 days

EPA action level:

4 picocuries per liter


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Half-life: 5730 yrsLive organisms maintain a fixed amount of C-14

C-14 decays to N-14 after death.

b geologic time.ppt

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