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Please Remember:
• Turn off Cell Phones and Laptops before class begins – these are distracting to other students.
• If you insist on talking during the lecture I will insist that you leave. This is getting to be an acute problem with a few students. I will not continue to try to speak over you. • Last day to withdraw without a grade is Oct. 3rd
Solar System Formation, Quick Review
• Something perturbs an interstellar gas cloud causing it to begin to rotate and contract due to gravitational forces. • As the nebula gets smaller is rotates faster (conservation of angular momentum) and therefore must flatten into a disk shape (due to centrifugal force) along its axis of rotation. It also heats up!• Star forms at dense center of Nebula.• Accretion of dust particles and atoms occurs – forming planetesimals.• Planetesimals accreate and form orbits within plane of disk.• Planetesimals which are not accreated into the 8 protoplanets are either trapped in the Asteroid Belt or ejected into either the Kuiper Belt (probably by Neptune) or Oort Cloud (probably by Jupiter and/or Saturn).• Protoplanets finish accreting nearby material and settle into their current orbits becoming the Planets as we now know them.• Finally an intense period of Solar Wind activity follows which expels the remaining gas from the original Nebula from the Solar System.
The Earth
From Apollo 17 on Dec. 7, 1972
General Features
Mass: MEarth
= 6 x 1024 kg
Radius: REarth
= 6,378 km
Density: = 5,500 kg/m3
Age: 4.6 billion years
Liquid Water!
Atmosphere!
Question
Why does the Earth have an atmosphere, while the moon does not?
A) The Moon is too close to the Earth to have its own atmosphere
B) The Moon is not massive enough
C) The Moon rotates too quickly on its axis
Escape Speed α √(mass/radius)
• Earth: 11 km/s
• Moon: 2.4 km/s
Explains why moon has no atmosphere.
Convection (occurs in Troposphere – the part of atmosphere closest to Earth's surface)
Convection also occurs when you boil water, or soup. Think of Earth's surface as a boiling pot.
Responsible for all weather & contributes to atmospheric heating
Heat competes with gravity to keep the atmosphere buoyant!
(DEMO)
Question
The Earth should reradiate all of the energy received from the Sun, giving the Earth a surface temperature of 250 K = -23o C.
Why is the average temperature of Earth so much (about 40o C) higher?
A) Gravity
B) Greenhouse effect
C) Tilt of Earth on its axis
The Greenhouse Effect
Main greenhouse gases are H
2O
and CO2 .
If no greenhouse effect, surface would be 40 oC cooler!
Questions
What are the major layers in the interior of the Earth?
How does density change with depth?
What about temperature?
Earth's Internal Structure
Mantle is semi-solid rock. Cracks allow material to rise => volcanoes.
Core temperature is 6000 K. Outer - Molten. Inner - solid. Metallic
How do we obtain information about the structure of the Earth's interior?
Like all waves, seismic waves bend or refract.
S-waves are unable to travel in liquid.
Measurement of seismic wave gives info on density of Earth's interior and which layers are solid/molten.
Earth's Interior Structure
Average density
CrustMantleCore
5,500 kg/m3
3,000 kg/m3
5,000 kg/m3
11,000 kg/m3
Density increases with depth => "differentiation" (DEMO)
Earth must have been molten once, allowing denser material to sink, as it started to cool and solidify.
Heating due to (i) bombardment and (ii) radioactivity
Bombardment by what? What important result do we see today?
Plates moving at a few cm/year. "Continental drift" or "plate tectonics"
Activity on the Earth's Surface
Question
What types of geological features or processes would you expect near plate boundaries?
What is the driving force behind the motion of the plates?
When plates meet...
1) Head-on collision (Himalayas)
2) "Subduction zone" (one slides under the other) (Andes)
3) "Rift zone" (two plates moving apart) (Mid-Atlantic Ridge)
4) They may just slide past each other (San Andreas Fault)
side view
top view
=> mountain ranges, trenches, earthquakes, volcanoes
What causes the drift?
Convection! Plates ride on top of convective cells.
One cycle takes millions of years => heat loss is extremely slow.
200 million years ago, all the continents were together!
Question
What causes the tides?
The Moon
= 3,300 kg/m3 (Earth 5,500 kg/m3)
= 1/6 that of Earth
Mass
Radius
Density
Gravity
= 0.012 MEarth
= 0.27 REarth
Humans First Visit the Moon - Apollo 11 Mission
At 10:56 p.m. eastern daylight time on Sunday, July 20, 1969, Neil Armstrong set his left foot on the moon and spoke the words that were to take their place among the great phrases of history:
"That's one small step for a man, one giant leap for mankind."
(Movie 1, Movie 2)
Tides
Tides are due to Moon's gravitational pull being stronger on side of Earth closest to it (Sun also influences tides).
Side of Earth closest to Moon feels slightly stronger pull => bulges towards it. Other side feels weaker pull => bulges away compared to rest of Earth.
The Earth spins once a day while the bulge always points towards and away from the Moon => two high and two low tides each day.
Tides (cont.)
Lunar Structure
Moon composed of material very similar to Earth's mantle!
The Lunar Surface● Dark areas: "maria"More recent lava flows.
● Lighter areas at higher elevation: "highlands".
● Many craters (due to meteorite impacts). Only important source of erosion!
● Highlands have 10x the crater density of maria => Highlands are older! maria highlands
How did the Moon form?
We're not quite sure! Two older theories:
1) "Coformation": The Moon and Earth formed out of the same material at the beginning of the Solar System. Problem: Moon has different density and overall composition...
2) "Capture": The Moon was a stray body captured into orbit around Earth. Problem: an extremely unlikely event & parts of compositions are similar...
So now, Impact theory preferred:
Early in Solar System, a Mars-sized object hit the forming Earth, ejecting material from the mantle which coalesced to form Moon. Computer simulations suggest this is plausible.
