Transcript Lecture 5

“It seemed the world was divided into
good and bad people. The good ones
slept better... while the bad ones
seemed to enjoy the waking hours
more.”
Woody Allen
http://sdbv.missouristate.edu/mreed/CLASS/A113Sp16
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The Earth-Moon System:
Features -vs- Interpretations
Some Examples
Round- means it is massively big.
well-defined features- solid
multiple colors- changes in temperature,
composition, or altitude.
Applying the scientific method
Which body is older, the Earth or the Moon?
Is there a way to know for sure?
Yes, radioactive dating (to be discussed)
Craters
Why is the Moon covered with craters, but the Earth
isn't?
Does the Earth have any craters?
Craters
Why is the Moon covered with craters, but the
Earth isn't? Does the Earth have any craters?
Erosion: resurfacing and weathering.
Types of erosion
Types of Erosion:
⇨
Wind
⇨
Rain & water run-off
⇨
Oceans & lakes
⇨
Vegetation
⇨
Plate motions- earthquakes
⇨
Volcanoes
In the continental U.S.
⇨
There are 16 visible (?) craters.
Back to: How can we determine the
age of the Earth?
For the surface
We can use radioactive (carbon) dating to tell how
old rocks we find are. When rocks solidify, they
lock-in the elements they are made of. The ½ life
of Carbon 14 (when ½ of the original carbon
would have been changed to nitrogen 14) is 5730
years. The ½ life of Potassium 40 (which decays
to Argon 40) is 1.25 billion years.
How old is old?
The oldest rocks found on Earth are
about 4 billion years old. Yet most
of Earth's surface is less than 200
million years old.
How do they know that the rock is really a
billion years old, or did it just have less
potassium 40 to begin with?
How do they know that the rock is really a
billion years old, or did it just have less
potassium 40 to begin with?
Compare the same type of rock from places
where you have an idea what the age is. From
around volcanoes, where the rocks are young,
to plains where the rocks are older. Also, take
core samples and compare the dates of rocks
from the surface of the core sample, to deep in
the rock.
How do they know that the rock is really a
billion years old, or did it just have less
potassium 40 to begin with?
...and perhaps most importantly, do
this for many different isotopes to
ensure consistent results.
From Moonrocks, it has been determined that the
highlands (light grey regions) are 4 to 4.5 billion
years old and the maria (the darker regions) are
about 3.5 billion years old.
highlands
Maria
Highlands
Maria
The mare is
moderately cratered.
While the highlands are
smothered in craters.
Saturated!!!
From the Moon
we get a
cratering
history: the
worst
bombardment
happened
before the mare
were formed
3.5 billion
years ago.
This will be our
age baseline for
the solar
system.
Surface age based on cratering
1) Smothered with craters; the surface is 4+ billion
years old. (e.g. Lunar Highlands)
2) medium (-heavy?) cratered; 3.5 billion years old.
(e.g. Lunar maria)
3) lightly cratered; ~200-500 million years old. (e.g.
Earth's surface)
4) no craters; <few million years old.
Quiz 1: how old is surface D?
A) <few million years
B) 100-300 million years
C) 3.5 billion years
D) >4 billion years
A
B
Assume the same scale for all pictures
C
D
A
B
100-300 million:
Earth-like
2-3 billion:
Maria-like
Assume the same scale for all pictures
C
3-4 billion: Not quite
saturated
Few million:
no craters
D
How old is the Earth, as a
whole?
How old is the Earth, as a
whole?
Current estimate: 4.6 billion
years old.
What about the insides?
How deep into the Earth have we
directly sampled?
What about the insides?
How deep into the Earth have we
directly sampled?
Deepest mine: TauTona- 2.4 miles
0.06% of the way.
Marianas Trench: nearly 6.8 miles
deep. 0.17% of the way.
Kola Superdeep Borehole: 7.5 miles
deep. 0.19% of the way.
What about the insides?
If we haven't directly sampled it,
how do we know what is at the
center of the Earth, or the Moon?
The structure of the Earth using
seismology
The Earth's structure: Density=5.5g/cc