If it were not for the oxygen in the Earth’s atmosphere, we humans would not be able to live. Today, oxygen makes up almost one fourth of our atmosphere.
However, at one time our atmosphere had almost no oxygen, and oxygen was poison to the creatures that lived on our planet.
Early in the Earth’s history, after its crust cooled and solidified, a spate of volcanic activity occurred, creating an atmosphere comprised mainly of nitrogen, ammonia, methane and carbon dioxide.
Living creatures on Earth probably obtained energy by taking in nitrogen-rich amino acids. Today, there are still some living things on Earth that do not breathe oxygen and survive in extreme environments, such as deep sea vents, where conditions are similar to that of early Earth. These creatures are known as extremophiles.
The evolution of photosynthesis as a means of obtaining energy completely changed the atmosphere’s composition. Oxygen is produced during the process of photosynthesis.
Now our atmosphere is made up of 78% nitrogen, 21% oxygen and small amounts of other gases, such as carbon dioxide and helium.
The atmosphere does more for us than just provide us with the oxygen that we need to breathe. It protects the …
Although the atmosphere may seem uniform when we look up at the sky, it changes dramatically from the lowest level near the ground to the highest region near outer space.
The troposphere is the atmosphere’s lowest layer. It contains about 4/5 of the atmosphere’s total mass. It varies in size, reaching all the way to about 11 miles (18 kilometers) above ground level at the equator. At the poles, the troposphere extends to only about 5 miles (8 kilometers).
Most of the water vapor in the Earth’s atmosphere is in the troposphere, and the troposphere is where weather happens.
In the troposphere, as altitude increases, the density of the air decreases and temperature decreases. At high altitudes, people can become deprived of oxygen because the lower air pressure makes it harder for oxygen to get pass through the lung membranes. Some people whose ancestors have lived in very high mountains, such as the Himalayas and the Andes, for a long time have developed physical adaptations to their respiratory and circulatory systems to account for the lower oxygen pressure.
The upper boundary of the troposphere is known as the tropopause. The temperature here is about -71 degrees Fahrenheit (-57 degrees …
A mirage is an optical illusion that is created when light rays are refracted (bent) as they pass through adjacent layers of air of different temperatures.
For example, suppose you are in desert where the Sun has warmed the sand, and this warm sand has heated up the layer of air immediately above it. Colder layers of air will lie above this hot thin layer.
Because hot air is less dense than cold air, light moves more quickly through hot air than through cold air. The change in the speed of light as it passes across the boundary between the air layers of different density causes the light to bend.
Imagine that you are standing on a sand dune somewhere in the desert. A group of palm trees is on a dune several hundred yards away from you. A layer of hot air lies between that dune and the dune on which you are standing.
You will see two groups of palm trees, even though there is really only one.
One image will come from light following a direct route across through the air.
The second image will appear upside-down below the first. It will have been created by light …
Light rays bending in a sky that is unusually heavy with moisture create strange and unsual light displays. Human beings have reported seeing such displays for hundreds of years.
Sometimes rings of light can be seen in the sky. The most common types of celestial rings are halos and coronas.
Halos, which are mostly seen in the winter, are created by the refraction (bending) of sunlight or moonlight by ice crystals floating high in the upper atmosphere.
Coronas may appear in an overcast summer sky. They are created when many tiny water droplets of uniform size, which are suspended in a thin cloud, are distorted by light waves.
Coronas may occur either singly around the Sun or Moon, or appear in sets.
Halos and coronas are usually almost colorless.
However, some of them can be very colorful, especially those that form around the Sun.
Smaller halos may possess vivid red interiors, changing to bluish white on their edges. The largest halos, if not pure white, show these same colors reversed, with the blue being on the inside.
Colored coronas are also blue on the inside.
The aureole, a type of poorly developed corona, ranges in color from bluish …