Lecture #13 Thursday, Feb. 15
Guest Lecturer: Prof. Sherrill
Handouts:
Notes:
- Due to poor
weather, the deadline for the Bonus Point Project #1 was extended for 1
week. It will be due Feb. 21.
In The News:
·
NEAR Collision with Eros.
The Spacecraft landed at 3:07 pm on Monday. Preliminary results: the last photo
was taken from 120 m above the surface. Here is the second to last image.
Today:
- Review
- The Earth
(continued)
- The Moon
- The Earth
(continued)
- Review
of the structure of the Earth.
- Plate
Tectonics
- Continents,
which are made of less dense material, float on the mantel and drift
over time.
- Convection
helps drive the motion.
- The Earth's Atmosphere
- The Earth's atmosphere
is relatively thin, and is about 100 km thick.
- It is made of mostly nitrogen (71%) and oxygen
(21%). Oxygen comes as a waste product of photosynthesis and
nitrogen from decaying plant and animal material.
- There are also small amounts of water vapor,
methane and CO2. These are greenhouse gasses. The
carbon-dioxide causes a greenhouse effect on the Earth that raises
the average temperature from -21 C to 14 C.
- The Ozone layer prevents harmful ultraviolet light
from reaching the surface.
- The Earth can keep its atmosphere because of its
high escape velocity of 11.2 km/s and that the average speed of air
molecules is well below this value.
- Earth’s
Magnetic Field
- Earth
is like a big magnet with a magnetic field that extends far out into
space.
- Metal
liquid core and rapid spin are needed for a strong magnetic field.
- The
Aurora (Northern Lights) are the result of the Earth’s magnetic
field.
- Life
on Earth
-
Life on Earth began almost as soon as
it was possible around 3.8 billion years ago.
- The one thing essential for life on Earth is liquid
water.
- Multi-celled organisms did not develop until about
1 billion years ago.
- From time to time there are mass extinctions. These
may be caused by collisions with large meteorites. The extinction of
the dinosaurs is thought to have been caused by a collision 65
million years ago.
- Half of species died at about the same time
- A worldwide layer of sediment has been found
dating to the same time.
- A candidate is the Chicxulub meteor crater in
Mexico. Other craters. Damage
- The
meteor that killed the dinosaurs was thought to be 6
miles wide.
- The
Moon
-
Basic Properties
-
Density 3.3 g/cm3
-
Gravity 1/6th that of Earth ( The moon has 1/80th the mass and
about 1/4 the radius)
-
No Atmosphere because the escape velocity is only 2.4 km/s.
DEMOS
- Rotational
period of 27.3 days. This means the Moon always keeps the same face
toward the Earth. The reason is that Moon is tidally locked to the
Earth.
- Surface
temperature ranges from -250 F to +250 F.
- Exploration
of the Moon
-
Luna Program (Soviet)
-
Luna 3 mapped the far side of the Moon in 1959.
-
Luna 9 landed on the Moon in 1966.
-
Apollo Program send and landed men on the moon from 1968 to
1972. See table 8.2 for details.
- Age of rock returned showed the Moon is the same
age as the Earth; 4.5 billion years old.
- Seismic stations showed the Moon has a cold,
solid interior
- The Moon does not have a magnetic field. This
also indicates no liquid core.
- Clementine
took detailed pictures of the Moon and showed hints for polar ice
caps.
- Lunar
Prospector (NASA) confirmed ice on the Moon (6 billion tons). Also
found that the Moon has a very small iron core.
-
The Lunar Surface (picture) (southpole)
- Comprised of highlands (older areas over 4 billion
years old), many impact craters, and Maria (Latin for sea). The
Maria are younger (3.3 to 3.8 billion years old).
- The highlands are very heavily cratered.
- The maria were formed latter by large impacts where
molten material flowed out to make the relatively smooth areas.
- The fine-grained sand all over the surface of the
Moon is from shattered rocks.
- Craters
on the Moon
- Cratering process
- Using Crater Counts to date planets
- See figure 8.16
- After about 4 billion years ago most of the
heavy bombardment stopped.
- Very heavily cratered areas in the solar system
must be older than 4 billion years.
- The Maria must be younger than 4 billion years
(rocks returned from them confirm this to be true).
- The
origin of the Moon - various theories
- fission hypothesis (The Moon broke off
the early Earth) - not accepted
- material should have fallen back to Earth
- the moon should have been in the Earth’s
equatorial plane; it is in the ecliptic plane
- the hole for the Pacific ocean was formed by
continental drift
- sister hypothesis (Earth and Moon formed
together) – not accepted because it does not explain why the Moon
lacks iron.
- giant impact theory - most accepted
- the Earth suffered a giant impact in its early
stages of formation, while the surface was still molten, with a
body perhaps the size of Mars.
- can explain the chemical composition due to the
intense heat generated in the collision.
- it could explain the gold and platinum in the
surface layers of the Earth.
- capture hypothesis (Earth’s gravity
captured a stray object) - not very likely because you need a third
body to carry away kinetic energy.