Exam 2 Postponed

Tuesday, November 12

Covers Chapters 7-10, & 14

One sheet of notes with writing on one side only

The Greenhouse Effect and climate change

Human activity is increasing the amount of CO2 in Earth’s atmosphere.

Is warming due to carbon dioxide?

The “little” ice age (16th- 19th centuries) – lower global temperatures, lower than usual number of sunspots and presumably solar activity.

The solar wind has been getting stronger.

Carbon-14

Carbon-14 levels have been dropping. Carbon-14 is produced when cosmic rays hit a carbon atom in a carbon dioxide molecule. During periods of strong solar activity, the cosmic rays can be swept from the solar system, causing less C-14 to be produced.

How can the increased solar wind heat the Earth?

No one knows.

What’s the big deal?

Simulations indicate that the average temperature on Earth will rise 2 degrees per century. So what? I like warmer temperatures.

71% of the Earth is covered with liquid water. As the temperature of the water increases more will become a vapor, which enhances the greenhouse effect and raises the temperature even more.

The run away greenhouse effect

Run-away greenhouse effect may be responsible for Venus

Early in Venus’s history, it probably had as much water as Earth obtained through bombardment. It may have had oceans and possibly even life.

Water vapor is also a greenhouse gas

If water vapor pressure exceeded 20% of Venus’s atmosphere, any oceans which might have existed would evaporate due to the added greenhouse effect. The more water that evaporates, the greater the greenhouse effect becomes.

Discussion

Venus has very little water vapor in its atmosphere. What might have happened to it?

Discussion

Why are the water molecules broken up in the atmosphere of Venus, but not in the atmosphere of the Earth?

Where did Venus’s water go?

Venus does not have an ozone layer to block UV light. UV light is energetic enough to dissociate water molecules. The gravity of Venus is not strong enough to hold the hydrogen and it escapes into space. The oxygen helps form sulfuric acid.

How do we know?

Sheer bad luck. A drop a H2SO4 got stuck in the intake of the Pioneer Venus atmospheric probe’s mass spectrometer. As the probe descended in the atmosphere this drop slowly evaporated.

But, this allowed the measurement of the hydrogen to deuterium ratio.

The results

Earth’s oceans contain one deuterium atom per 6000 hydrogen atoms.

But the drop that clogged the mass spectrometer’s intake had 120 times as much deuterium.

Discussion

How could Venus have ended up with so much more deuterium than the Earth, if we think they both started out with the same ratio of hydrogen to deuterium?

Will Earth be worse than Venus?

If Earth’s oceans were to evaporate the atmosphere would be dominated by water vapor and have a pressure 400 times its current value. The added greenhouse gasses would heat the carbonate rocks and cause them to release their CO2 increasing the greenhouse effect still further and raising the pressure another 70 bar.

Venus is very likely telling us the fate of the Earth.

Even without humans, as the Sun builds up helium in its core, the core will contract and heat up. The future Sun will be brighter and hotter. Thus a run away greenhouse effect on Earth is inevitable.

The Martian Atmosphere

Carbon dioxide 95.3%

Nitrogen 2.7%

Water 0.03%

Pressure 0.007 atm.

The greenhouse effect

The greenhouse effect on Mars raises the surface temperature only about 6 degrees C. This keeps the average surface temperature of Mars well below the freezing point of water.

The Martian atmosphere, which has a surface pressure 100 times less than Earth’s, is too thin for liquid water to exist on the surface, even where the temperature gets above freezing.

Water will boil on the surface of Mars at temperatures above 0 degrees C.

Mars had liquid water in the past

The old, heavily cratered southern highlands have channels, valleys, and gullies which appear to have been made by flowing water.

The northern lowlands may even have been an ocean.

The Martian atmosphere must have been denser in the past.

Discussion

On Earth what is the difference between the crust of the ocean basins and that under the continents?

Crustal thickness

On Earth the oceanic crust is 30 km thinner than under the continents.

The orbit of Mars Global Surveyor indicates the crust of Mars is about 40 km thick under the northern lowlands and 70 km thick under the southern highlands. But the boundary between thin and thick crust does not correspond to the boundary between lowlands and highlands.

Layered deposits

Ma’adim Vallis

Gusev crater, the Spirit rover landing site is at the top

Discussion

If Mars was so much like Earth in the past, what happened to make it so cold and have such a thin atmosphere today? What happened to the gasses that made up the earlier, thicker atmosphere?

Carbon dioxide cycling fails

Mars is too small to retain enough heat to the present day to provide enough volcanism to return carbon dioxide to the atmosphere that is now trapped in carbonate rocks buried under the Martian regolith.

Once volcanism shut down on Mars, the atmosphere could escape into space. As Mars became colder, carbon dioxide froze out of the atmosphere at the poles, creating the polar ice caps.

Discussion

Where did all the water on Mars go?

Martian clouds

Not into the atmosphere

The Martian atmosphere contains less water than is in lake Erie.

The polar ice caps?

No one knows how much water may be contained in the Martian polar ice caps.

Martian polar ice caps also contain dry ice, frozen carbon dioxide.

Northern polar layered deposits

Permafrost

Most of the Martian water may be retained under the surface as a layer of permafrost.

Chaos and channel

Elysium Crater

Sirenum Fossae Trough

Subsurface hydrogen map

Phoenix Lander site

Spitsbergen Island

Terrestrial planet uniqueness

Earth

1. Has plate techtonics2. Has liquid water of the surface3. Has life4. A large Moon

The moons of Mars

Mars has two small moons. The Martian moons have similar properties the asteroids in the nearby asteroid belt. Thus the two small moons of Mars are speculated to be captured but may have been formed with Mars.

The moons of Mars

Discussion

Phobos, the larger moon of Mars, orbits Mars in 7 hours 39 minutes, much faster than Mars rotates. Considering tidal friction, what does this mean for the future of Phobos?

Phobos

Because Phobos orbits Mars faster than the planet rotates, the tidal forces from Phobos try to pull Mars into rotating faster, which causes Phobos to lose orbital speed. Thus Phobos is slowly spiraling into Mars and will crash into the planet in about 40 million years.