When it comes to discussing the weather, most people can hold up their end of the conversation. After all, who doesn't have an anecdote about how a rainy day disrupted their plans? Weather is all around us, affecting every aspect of our lives. It's no wonder discussion of it fills our awkward pauses and doomed first dates.
This view of the weather, as something that happens around our lives -- is the first concept you have to abandon to gain a clear understanding of how Earth's atmosphere works. Forget that cloudy days make you sad or that you hate shoveling snow. Even put aside the idea of weather as something that happens to a city or region. The weather is simply the state of the atmosphere, the gaseous layer that serves as the outermost barrier between Earth and the rest of the universe..
While water covers 71 percent of Earths' surface, the atmosphere envelopes all of it. But this layer of gases doesn't just sit there, it's subject to influence from a host of terrestrial and extraterrestrial forces. Think of the atmosphere as a lucky man or woman who has just won the lottery. Suddenly, everyone seems to have a few suggestions on how he or she should spend his or her time and money. Uncle Joe says one thing, Aunt Clara another. Before you know it, everyone seems to have some sort of input into the winner's daily life.
For Earth's atmosphere, gravity, sunlight, oceans and topography all dictate certain cycles of air movement -- some very localized, others concerning vast portions of the planet. In addition, a number of these various cycles affect each other, spinning off new cycles and brewing clouds, precipitation and an unending torrent of storms. All of these various atmospheric responses are what we know as the weather.
With all of these various influences, Earth's atmosphere is quite an intricate system. No wonder it's so hard to predict the weather. In this article, we'll unravel that intricate system, starting from space with the big picture and moving steadily back down to the level you experience every day
Evolution of the Atmosphere
Go back about 4.6 billion years and you wouldn't find the Earth. You'd find molecules and particles slowly forming a gaseous mass inside a nebula. Over time, these gases eventually condensed into liquid and solid forms. Some of it cooled to form the continents and oceans, but much of Earth's center still burns with furious heat. The atmosphere sits on the surface of this sphere.
Scientists think Earth's original atmosphere escaped from within the planet, where it formed in the heat of radioactive decay. By today's standards, this air was utterly unbreathable; rich in methane, ammonia, water vapor and neon. There was no free oxygen (O2) at all. You might think this had to change before organisms could evolve on the planet, but it was actually the steady evolution of unicellular organisms that produced oxygen and brought about the change in the atmosphere's makeup. Over hundreds of millions of years, this evolved into the air that fills your lungs today.
Currently, the atmosphere is composed of 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon and 0.03 percent carbon dioxide. The remaining 0.07 percent consists of water vapor, hydrogen, ozone, neon, helium, krypton and xenon [source: Vogt]. Is this the finished recipe for Earth's atmosphere? Probably not, considering that the process of evolution that created it continues to this day. Plus, there's another agent of change to consider: human beings.While some date human influence on global climate back to the industrial revolution of the 1800s, others look back several thousand years to the agricultural revolution. Environmental scientists such as William F. Ruddiman argue that carbon dioxide concentrations began to rise 8,000 years ago due to early slash-and-burn agriculture practices in Asia, India and Europe. To learn more about humanity's role in climate change, read How Global Warming Works.
So we've covered how the atmosphere developed and what it's made of, but we're still looking at the Earth from the outside. In the next section, we'll move in a little closer and explore the major physical properties at work in it.
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