Calculating Ages of Solar System
objects
Radiometric dating
Cratering
Sequencing
____________________ using
radioactive decays
P
Parent
Element
D
Daughter
Element
Half-life – __________________________________________.
Examples of radioactive isotopes - ________________ half-life = 4.5 Gyr
232Th
half-life = 3.5 Gyr
____ half-life = 6,000 yrs (Carbon dating)
See also pages _______ for more on radiometric dating!
Fill this in based on the next slide.
Number of Time Number
of
half lives (years)
Parents
0
1
2
3
4
5
Fraction
parents
still left
Number of
Daughters
# Daughter/
# Parent
Assume we’re doing Iron-60 dating. It has a half-life of 5 million years
Radioactive Decay, cont.
At time = 0, the rock formed
1 half-life later…
______ yrs total
______ yrs total
______ yrs total
After 2 half-lives
After 3 half-lives
______ yrs total
______ yrs total
4 half lives
5 half-lives
After 6 half lives …
Clicker
question
now
How many parents are left
after 2 half lives?
1. 8
2. zero
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Do you think Carbon dating is effective for a 1
million year old fossil?
1. Yes
2. No
0
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Why or why not?
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Element P decays into element D with a half-life of 10 million
years. You find 3 times as many daughters as parents. (D/P = 3)
How old is the rock?
1.
2.
3.
4.
5.
6.
0
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5 million years
10 million years
20 million years
30 million years
40 million years
I have no clue
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You find an animal skeleton that has 1/8th as much carbon14 in it as living samples have. How old is the skeleton?
1.
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3,000 years
6,000 years
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24,000 years
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Radiometric dating
• Any questions?
• ______________ dating __________:
– ____________________________ if using __
– Radioactive dating
– Radioisotope dating.
– I won’t call it by these names. These names won’t
be on your test.
Review: Simplified History
Formation - _____________ ago
Present
______________________________
_________________________________
Recall: 1 Gyr = ___________________
How old are the planets in the solar system?
This history was determined by
_____________________
________________________!
Note: the Sun is ________ years old. It’s ______ burned out.
How much longer will it last?
Crater Formation
Before
______________! Why is 11 km/sec minimum?
Rocky or icy objects (also called ___ & ___ )
This is going to leave a mark…
Impact site’s ground gets vaporized. So does
the impactor!
Craters
An object this size
Will make a crater this big!
Diameter of crater is about ______diameter of rock. Depth of crater is
about _________the diameter of rock. See also p. ____
Crater _____
These streaks of ejecta are called “_____”.
________________________________ over
about _____________ years because
_____________________ chemically alters
them.
Most prominent under _______________
(at what time, locally?).
So, how can you find the youngest craters on the Moon?
rays
Crater Sizes
Small < 25 km
Big - up to 200 km
Note the central peaks
This puppy is the size of the L.A. basin!
And…
REALLY HUGE!!
Also known as “multi-ring impact basins”
Similar, but a bit
larger crater
formed on
Mercury, and on
the opposite side,
we see “weird
terrain” see page
____.
That just had to hurt.
Big crater on the Moon
How do we measure ages?
1. Relative dating – Principle of Superposition
Ordering of events based on appearance.
2. Crater counts – surfaces with _______________ are
new or old? Why? (see p. ____________)
3. Radiometric dating of rocks. (see also section 8.5)
Called “Carbon dating” when used on recent fossils.
Relative Surface Dating – Can you order the events?
A. Volcanic Eruption
B. Fault
C. Crater
D. Hills
E. Cratered Terrain
(Hint: old or new?
Created when?)
F. Crater
G. Crater
A Real Example - Iapetus
Iapetus is one of Saturn’s moons.
Picture taken by Cassini
Scarp (Shrinkage
quake) &
subsequent landslide
There is cratering
on ground. Do
you see many or
few craters in this
big crater?
What does that
tell you about the
circled crater?
Is old or new?
Crater Rim
Smaller
Crater
What can you say
about the age of the
small crater?
Landslide?
Iapetus – entire moon
• Diameter = 1460 km
• Here’s the “big crater” we
just looked at.
• Approx 500 km across
• Landslide is here.
• Ridge all along equator.
Mystery!
• In Fall 2009 – the
light/dark hemispheres
mystery was solved.
Ages
• Now you know how astronomers calculate
ages.
• Study for the last test.
• It is NOT cumulative.