Environmental Science: The Earth's Atmosphere

photosynthesis

process whereby green plants use sunlight to convert carbon dioxide and water into glucose, a high energy sugar, and oxygen

exosphere

the last layer of the atmosphere before space

troposphere

the layer of the atmosphere just above Earth's surface, where all our weather takes place

mesosphere

the middle layer of the atmosphere

atmosphere

the thin layer of gases that surrounds earth

Up, Up, and Away!

Before we can fly a kite or take a hot air balloon ride, we need to make the air that will keep it up there! What IS the air made of? Everyone knows that air has oxygen, but is that all? And where did the oxygen come from?

What You Should Know

Before you begin, you should: understand photosynthesis; understand the role of oxygen in photosynthesis.

OBJECTIVES

Define what makes Earth's atmosphere unique from other planets in our solar system. Compare and contrast the composition of Earth's ancient atmosphere with its current atmosphere. Explain the significance of living organisms in the creation of an oxygen-rich atmosphere. Differentiate between the composition and function of each layer of the Earth's atmosphere.

ozone

an oxygen compound (o3) that in earth's stratosphere helps protects us from harmful radiation originating in the sun

thermosphere

an upper layer of the earth's atmosphere

The Atmospheres of Earth and Venus

Do all of the planets in our solar system have the same atmospheric composition? To answer that question, let's compare the Earth to one of its neighbors, Venus. When you compare the two atmospheres, there are some significant differences. One example is the amount of oxygen present. Photosynthetic bacteria on Earth produced oxygen that allowed the majority of life on the planet to evolve. Venus, however, is another story. The atmosphere of Venus makes it impossible to support life as we know it for the following reasons: Too much carbon dioxide can kill non-photosynthetic organisms—like humans. Carbon dioxide traps heat from the sun, which makes the surface of Venus 470 degrees C, a temperature that is uninhabitable to most known life forms. Clouds that swirl over Venus are made of sulfuric acid, which rains acidic precipitation over the entirety of the planet and destroys plants and other photosynthetic life forms. The atmosphere of Venus also makes space travel to the planet difficult. If you tried to land a spaceship on Venus, you'd first have to maneuver through the thick acidic clouds. If you managed that, you would then be subject to the hurricane-force winds that blow around the planet on a regular basis. If you even made it out of your spaceship, you'd be breathing poisonous air hotter that anything you've ever experienced on Earth. All these factors would make Venus an unattractive vacation destination, to say the least. Take some time to learn more about the atmosphere of Venus.

LET'S REVIEW

Here are some key ideas you have learned from this lesson: The atmosphere is the thin layer of gases that surrounds Earth. Earth's atmosphere consists mostly of nitrogen and oxygen. Earth's early atmosphere contained no oxygen. Oxygen first began to accumulate in the atmosphere after the onset of photosynthesis from early bacteria. The layers of the atmosphere are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Ozone is an oxygen molecule that, in the stratosphere, protects Earth from harmful radiation from the Sun. Air pressure is a measure of the force a column of air exerts on a point on Earth. Air pressure decreases with increases in altitude, or distance above sea level.

PHOTOSYNTHESIS AND THE ATMOSPHERE

Thanks largely to photosynthesis, we now have an oxygen-rich atmosphere on Earth. The atmosphere is a layer of air that protects our Earth from harmful UV radiation. It is also a layer of gases which traps and maintains heat so that life can exist on Earth. Composed mostly of nitrogen and oxygen, the atmosphere is made of four distinct layers. Troposphere—The troposphere is the layer closest to the earth surface. This is where all the weather events occur. Most of the water vapor and dust particles found in the atmosphere are found in this layer. Stratosphere—This is the next layer above the troposphere. Because weather occurs much lower in the atmosphere, planes often rise into the stratosphere to avoid thunderstorms and turbulence. The ozone layer, which protects us from harmful UV radiation, is found in the stratosphere. Pollutants such as CFCs can destroy our ozone layer, creating a hole in it and increasing rates of skin cancer and other cancers worldwide. Mesosphere—The mesosphere is the third layer up above earth. The mesosphere is hard to study because instruments, such as weather balloons and airplanes, cannot fly there. We do know that the temperatures in the mesosphere are very cold and that rock fragments from space burn up when entering this layer. Thermosphere—This is the outermost layer of the atmosphere before reaching space. It gets very hot in this part of the atmosphere because of its exposure to the sun. The air in the thermosphere is very thin, and many satellites—as well as the International Space Station—orbit the earth in this layer of the atmosphere.

Atmospheric Pressure

The gas molecules of the different elements that make up the atmosphere can move freely. The molecules are the most compressed and dense at the Earth's surface. The densest part of the atmosphere is found at sea level. The weight of the air exerting force on Earth's surface results in air pressure. Like density, air pressure decreases with altitude, which is a measure of the distance above sea level. At sea level the average air pressure is 1.2 kg/m3. Take a look at the picture of the water bottle. The empty bottle was capped at an altitude of 2000 m, and the air inside the bottle maintained the air pressure that existed when it was capped. The bottle was then brought back to sea level. The higher air pressure at sea level crushed the bottle.

ATMOSPHERE

What are you doing right now? If you listen carefully, you may notice that you are breathing in and then breathing out. You are contributing to the process of respiration. Most everyone knows that we take in oxygen to breathe and let out carbon dioxide. What about plants? What do they do? As animals take in oxygen and let out carbon dioxide, plants are doing the opposite. They take in carbon dioxide and release oxygen back into the atmosphere. This is known as photosynthesis. According to evidence found in the rock record, photosynthesis began on Earth about 3.5 billion years ago. Feeling a little rusty on the subject? Check out this following link for a review: Photosynthesis. Launch the interactive when directed to this page. Now that we know that plants and animals are part of a delicate cycle of exchanging carbon dioxide and oxygen, think about this: What was in the air when the Earth was formed? If there were no plants, animals, algae, or even bacteria to make or use oxygen, then what was in the atmosphere?

Earth's Atmosphere

You probably have a general idea of what is meant by the term atmosphere. It is the thin layer of gases that surrounds our planet. If you take a deep breath right now, what chemical elements would you breathe in? The pie chart displays the components of Earth's atmosphere. The second smaller blue graph shows the minor elements and gases that compose 0.038 percent of the atmosphere.

stratosphere

a layer of the earth's atmosphere that contains the ozone layer