Review-Unit3

Troposphere §

The troposphere is the lowest level of the atmosphere. This is where we get phenomena like weather and convection, and is where most of the greenhouse warming occurs.

Stratosphere §

Where ozone absorbs ultraviolet light from the sun. Begins where the temperature stops dropping and instead begins to rise with altitude. It is heated by UV light, and there is no convection that occurs here

1. Infrared
2. Visible
3. UV
4. Xray

Reflection §

While some gases technically have more potential for warming if all gases were released in the same amounts and lasted the same amount of time, the actual most potent gases are the ones that stay in our atmosphere for a very long time since they build up quickly, despite their lower per unit potency.

Atmospheres §

Earth §

1. Earth’s temperature remained cool enough for liquid oceans to form.
2. Oceans dissolve atmosphere $C{O}_2$.

Most of Earth’s carbon and oxygen is in rocks, leaving a mostly nitrogen atmosphere. Plants release some oxygen from CO${}_2$ into the atmosphere. Life is what caused the oxygen in our atmosphere, which led to us; this did not happen on Venus.

Ultraviolet light can break up O${}_2$, allowing ozone (O${}_3$) to form in the stratosphere. Without plants to release O${}_2$, there would be no ozone in the stratosphere to absorb ultraviolet light.

Cooling allows CO${}_2$ to build up in the atmosphere, while heating causes rain to reduce CO${}_2$ in the atmosphere.

Carbon Dioxide Cycle §

The carbon dioxide cycle allows the Earth to self-regulate its temperature.

1. Atmosphere CO${}_2$ dissolves in rainwater.
2. Rain erodes minerals that flow into the ocean.
3. Minerals combine with carbon to make rocks on the ocean floor.
4. Subduction (happens in regions where the ocean floor goes back into the molten mantle; think tectonics) carries carbonate rock down into the mantle.
5. Rock melts in the mantle and CO${}_2$ is outgassed back into the atmosphere through volcanos; the cycle starts again.

If you could take a sample of the mantle, it would have carbon in it no matter what; however, volcanos are the way that escapes.

Long-Term Climate Change §

Changes in Earth’s axis tilt might lead to ice ages. Widespread ice tends to lower global temperature by increasing Earth’s reflectivity. CO${}_2$ from outgassing will build up if oceans are frozen.

The Sun §

Basic Properties of the Sun §

Property	Value	Earths x
Radius	$6.9\times 10^8$ m	109
Mass	$2\times 10^{30}$ kg	300k
Luminosity	$3.8\times 10^{26}$ watts

What even is the sun? §

The sun isn’t on fire— we need to take a closer look. If it was on fire, it would only last for about:

$$\frac{\text{Chemical energy content}}{\text{Luminosity}}\approx 10\text{k years}$$

which we know is far too short a time. The sun isn’t contracting either; if it was, it would only last for:

$$\frac{\text{Gravitational potential}}{\text{Luminosity}}\approx 25\text{ million years}$$

It is actually powered by nuclear energy ($e=m{c}^2$)!

$$\frac{\text{Nuclear potential energy (core)}}{\text{Luminosity}}\approx 10\text{billion years}$$

The sun is essentially in a state of gravitational equilibrium, where the weight of the upper layers compress the lower layers with the same amount of pressure as the outward pull of the Sun’s internal gas pressure.

The rate at which energy radiates from the surface of the Sun must be the same as the rate at which it is released by fusion in the core. Otherwise, gravitational equilibrium would not be able to remain stable. Gravitational contraction has provided the energy that heated the core as the Sun was forming, but contraction stopped when fusion began. The sun has enough hydrogen to shine for about 10 billion years.

What is the structure of the sun? §

From the inside out, the layers of the sun are the:

• Core
• Radiation zone
• Convection zone
• Photosphere
• Chromosphere
• Corona

Energy moves through the core and radiation zones through a process called radioactive diffusion, in which photons bounce randomly amongst gas particles. After energy emerges from the radiation zone, convection carries it the rest of the way to the photosphere, where it is radiated into space as sunlight. Energy produced in the core takes hundreds of thousands of years to reach the photosphere.

How does nuclear fusion occur in the sun? §

Because the core of the Sun is so extremely hot and dense, it makes the perfect environment for the fusion of hydrogen into helium, via a proton-proton chain. Because the fusion rate is extremely sensitive to temperature, gravitational equilibrium acts as a thermostat to keep the fusion rate steady.