Back To CourseBasics of Astronomy
28 chapters | 325 lessons
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Our beautiful and homey planet, Earth, is very different today compared to its ancient past. Four billion years ago, when the Earth was forming, you wouldn't have been able to breathe, you would have fried from the dangerous radiation coming from the sun, and you would have ducked for cover left and right as furious volcanoes erupted all over the place.
That was the nature of Earth back then: inhospitable and deadly. It is much different from the beautiful, life-giving planet we call home today. How did we get from one to the other? How do we as humans impact the evolution of Earth's atmosphere today? This lesson will teach you that and more.
Billions of years ago, Earth's atmosphere was likely filled with rich amounts of carbon dioxide, nitrogen, and water vapor that was outgassed, or released, from the Earth's interior as a result of high levels of volcanic activity. Over time, things, thankfully, changed.
Like the bubbles in a soft drink prove, carbon dioxide can easily dissolve in water. When carbon dioxide combined with things like calcium in our oceans to form limestone, it helped remove its dangerous and excessive levels from the ancient atmosphere on Earth.
Meanwhile, about 2-2.5 billion years ago, photosynthetic plants had appeared in numbers large enough to produce oxygen at a rate faster than it was being removed by chemical reactions in the ancient Earth. As a point of clarity, photosynthesis is a process that produces energy for plants by absorbing carbon dioxide and releasing oxygen.
What I just described should make it evident to you that life on Earth doesn't exist because of oxygen. Most of life on Earth doesn't need oxygen. Our current levels of oxygen came to be mainly because of life itself.
Nowadays, air, a mixture of gases making up Earth's atmosphere, consists of 78% nitrogen, 21% oxygen, and 1% of gases, like argon and carbon dioxide. Of course, other things, like water vapor, dust, industrial pollutants, and even microbes are found in the air as well.
With every step you take and every move you make, you need to breathe in air to power your body, but with every breath you take, you might be breathing in a deadly virus. It's a tradeoff; one that's well worth the risk though.
Half of the air I described is found in the first four miles above the Earth's surface, and the total mass of the Earth's atmosphere is 5,000 trillion tons. That sounds like a lot, but it's actually only about one-millionth the mass of Earth itself.
It is Earth's force of gravity that keeps this atmosphere from floating away into space, although some atoms do escape into space at the top of our atmosphere.
Prior to enough oxygen (O2) accumulation in the Earth's atmosphere, an ozone layer could not form. The ozone layer is a protective layer of oxygen ions (O3) lying 15-30 km, which is about 9-19 miles above the Earth's surface. Before the ozone layer, the sun's ultraviolet radiation - the stuff that gives you skin cancer and harms plants we need - could easily pass through the Earth's atmosphere.
But as the Earth's atmosphere evolved and oxygen (O2) levels increased within it, these oxygen molecules were split by the sun's UV rays, like a sword slicing through a rope connected to a ball at either end. This process formed single oxygen atoms. When one oxygen atom combined with the remaining oxygen molecules, simple math dictates you get O3, which is ozone. These ozone molecules are really good at absorbing the dangerous UV rays coming in from space. Basically, the pale blue ozone layer is a force shield that blocks bullets - that is to say UV rays - coming from space that are trying to hurt us and life on Earth in general.
Some of this protective ozone, which also protects plants vital to our survival, is being destroyed by things like chlorofluorocarbons released by aerosol sprays, air conditioners, and refrigerators. This, and other chemicals, revert the ozone back into ordinary oxygen (O2) molecules, which doesn't block UV radiation. This means UV radiation increases at the Earth's surface and harms life, including yourself, as a result.
But don't get the ozone protecting us way up high confused with the ozone produced as a result of human industrial and automotive pollution! Yes, breathing in ozone produced by these methods is harmful to our health. It can cause irreversible lung damage! We do need ozone though; except, we need it higher up, where it helps us, not hurts us.
Human pollution is unfortunately another cause of something you have already heard of: global warming. Global warming, for those of you who are unsure of what it is, is related to the greenhouse effect. The Earth's atmosphere lets sunlight through to the surface of the Earth. We need this light so that our crops can grow and the animals we eat can get fed.
The surface of the Earth absorbs this sunlight as well, gets warm, like you get warm when bathing in sunlight, and radiates back infrared radiation. Carbon dioxide and other gases trap infrared radiation, just like your car's windows or a greenhouse's glass traps it inside on a hot day. This trapping of heat makes the Earth warmer. Without the greenhouse effect, our Earth would be about 54 degrees Fahrenheit, which is about 30 degrees Celsius cooler than it is now, and humans wouldn't exist.
The big point here is that over billions of years, CO2, the glass-like, heat-trapping gas responsible for the greenhouse effect, has been carefully removed from the atmosphere and stored in places like oil, natural gas, and coal. Humans have dug up these carbon sources, burned them, and released the buried CO2 back into the atmosphere far more quickly than Mother Nature can remove it. Such an increased concentration of CO2, increasing the greenhouse effect, is causing global warming.
Actually, recent evidence has conclusively shown that the levels of CO2 added to our atmosphere since the year 1800 have been almost entirely due to human pollution. Global warming is occurring because of human pollution and not as a result of normal and natural cycles in the Earth's climate, axis inclination, or sun's luminosity, as climate change deniers have proposed for so long.
In fact, studies of growth rings on old trees have shown that the Earth was actually cooling for the majority of the last 1,000 years, but human intervention, mainly in the 20th century, has reversed this trend.
Earth's ancient atmosphere was filled with carbon dioxide, nitrogen, and water vapor that was outgassed, or released from the Earth's interior as a result of high levels of volcanic activity. Over time, this atmosphere evolved into the one we have today.
About 2-2.5 billion years ago, photosynthesis, a process that produces energy for plants by absorbing carbon dioxide and releasing oxygen, began to increase the levels of oxygen on Earth, while excess carbon dioxide was stored in places like our ocean. Nowadays, air, a mixture of gases making up Earth's atmosphere, consists of 78% nitrogen, 21% oxygen, and 1% of gases like argon and carbon dioxide.
Prior to enough oxygen (O2) accumulation in the Earth's atmosphere, an ozone layer could not form. The ozone layer is a protective layer of oxygen ions (O3) lying 15-30 km above the Earth's surface. The ozone layer, like global temperature, is directly, significantly, and negatively impacted by human industrial pollution.
At the end of this lesson you should be able to:
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Back To CourseBasics of Astronomy
28 chapters | 325 lessons