Article by Yowan Dias, 3rd Year Undergraduate, Faculty of Science, University of Colombo
In the beginning, 4.6 billion years ago, the Earth was a hellish landscape. Devoid of water and air, it was anything but the bluish planet we inhabit today. Scientists believe that the Earth collided with a Mars-sized planet half a billion years after the beginning of the universe, releasing so much energy that the surface of our beloved planet melted and caused the Earth’s then-atmosphere, which most likely only consisted of hydrogen and helium, to get vaporized into space.
For billions of years, the Earth’s landscape was but a hellish one, with fiery flames and hot magma blanketing the Earth’s surface. The fumes and smoke released by the worldwide magma ocean seeded the formation of the oldest version of the atmosphere we have today. The air began to get filled with gases such as methane, water vapor, ammonia, and carbon dioxide, making the early atmosphere a chemically reducing one. Along with these gases, nitrogen would have been liberated from volcanic eruptions, which owing to its unreactive nature, gradually built up over time, making it the most abundant gas in the Earth’s contemporary atmosphere.
As time passed (about half a billion years), the Earth started to lose its heat, cooling down enough for the surface to solidify and for water vapor to condense, precipitate and form the early oceans. As the oceans started to form, much of the carbon dioxide started to get dissolved in them. With the evolution of photosynthetic organisms in the oceans, oxygen started to saturate the seas and diffuse into the air above, changing the composition of the atmosphere. As oxygen concentrations in the atmosphere started to build up, the ozone layer began to materialize, since ozone is formed when oxygen molecules interact naturally with solar radiation. Over the new few million years, the carbon dioxide levels started to plummet while oxygen levels multiplied. This resulted in the composition of the modern-day atmosphere which contains 78% nitrogen, 21% of oxygen and carbon dioxide making up only 0.04%.
The Layers of the Blanket
If you were to arrive to Earth from the vast expanse of space, say in a space rocket, you would be first greeted by the outermost layer of the Earth’s atmosphere: the exosphere. It begins about 700km from sea level and extends to space to about 10,000 km. At the outermost region of the exosphere, it starts to merge with the solar wind, which consists of streams of particles that are emitted from the Sun. The Aurora borealis and Aurora australis, colloquially known as the Northern and Southern lights, form at the lowest region of the exosphere. The exosphere is also where most satellites orbit the Earth. Lying below the exosphere 80 km above the Earth’s surface is the Thermosphere. This region gets its name as the temperature increases with increasing altitude. This phenomenon occurs due to the lower density of air molecules in the region. The thermosphere also lacks clouds and water vapor and is home to the International Space Station.
As your rocket starts to progress further through the layers, it would start to heat up in the atmospheric layer known as the mesosphere, which is found sandwiched between the upper thermosphere and lower stratosphere. It’s in the mesosphere that meteors burn up. Noctilucent clouds, the highest clouds in Earth’s atmosphere, form in this layer.
Below the mesosphere lies what is perhaps one of the most important layers of the atmosphere: the stratosphere. Housing the ozone layer, the stratosphere protects the Earth from harmful ultraviolet radiation by absorbing most of the rays that come from the Sun. Owing to this, the stratosphere becomes warmer the higher up you go. The stratosphere is also the highest layer in which aircraft such as jet planes can reach.
Finally, we come to the troposphere – the lowest layer. This is where most of the air in the atmosphere gets concentrated. All weather phenomena, including the formation of almost all clouds, takes place within the troposphere.
Credit: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith
The Science of the Skies: Atmospheric Physics
As with every natural process or phenomenon that occurs, there’s good old science to explain it. Since physics is the branch of science that deals with natural processes and how they come to arise, it’s a no-brainer that physics is involved in describing the processes of the atmosphere. Atmospheric sciences have been broadly categorized into three: meteorology – the study of and forecasting of weather, climatology – which involves the study of atmospheric trends and patterns over a long term, and aeronomy – the study of the upper parts of the atmosphere.
Zooming in on meteorology, this field deals with recording and analyzing day-to-day variations in weather, mostly within the confines of the troposphere and the lower stratosphere. Climatology is an extension of meteorology, involving the study of long-term variations in weather, from periods of a month to about millions of years. Meteorology employs the use of various models and theories such as scattering theory, wave propagation models, spatial statistics, and statistical mechanics, which can be used to elucidate atmospheric processes.
The meteorological discipline, not surprisingly, has important implications, affecting every aspect of our day-to-day lives. As the weather affects many fields of work, from agriculture and fisheries to tourism and travel, understanding the atmosphere and its various processes have become crucial now more than ever.
Out of this World: Atmospheres on Other Planets
The Earth isn’t the only celestial body to possess an atmosphere. Apart from Mercury, which had most of its atmosphere blasted off into space due to solar winds, all other planets in the Solar System have atmospheres. Earth’s atmosphere is unique from those of other planets due to the presence of molecular oxygen which was liberated through biological processes such as photosynthesis.
From the planets in the Solar System, the award for harshest atmosphere would probably go to Venus. Considered the most inhospitable place in the Solar System, Venus is home to a dense atmosphere, rich in carbon dioxide, 90 times the concentration found on Earth. This causes an extreme greenhouse effect, trapping so much solar radiation that temperatures can reach up to 460°C. That’s not all that makes Venus a hellish place. The rain that falls on the planet contains corrosive sulfuric acid. Despite the high heat, Venus has ‘snow’ which unlike the snow we are familiar with, is made of basalt frost, formed from metals that were vaporized by its atmosphere. Furthermore, a large vortex exists in Venus’ south pole, roughly the size of Europe. This vortex spins at about 400 kilometers per hour, faster than the rate at which the planet rotates.
Mars is a planet known for its dust storms that at times – such as in 2018 – have engulfed the entire planet. These occur due to the heating of the atmosphere which causes dust to be raised off the ground. “Dust Devils” are another type of atmospheric phenomenon which is a type of miniature tornado that move across Mars’ surface.
Atmospheric processes can be quite iconic. The Great Red Spot of Jupiter is in fact a raging hurricane, a storm spanning 16,000 kilometers across (that’s about 1.3 times the width of the Earth), and Jupiter’s north and south poles are blanketed with arrays of cyclones. Meanwhile Saturn gives a strong competition with more intense atmospheric activity. With lightning strikes 10,000 times more powerful than the Earth’s, the gas giant is known to have storms that envelop the entire planet. Furthest away from the Sun, Neptune, containing an atmosphere primarily made up of methane, possesses the fastest winds in the planets of the Solar System. With storms that come and go that have baffled scientists, the “Great Dark Spot” on the planet’s surface is in fact one of Neptune’s hurricanes.
Anywhere the Wind Blows
Weather phenomena has been one of mankind’s many fascinations. From turbulent tornadoes to horrendous hailstorms, the atmosphere is an extremely dynamic and complex system. We quite often fail to notice this invisible yet mysterious natural entity. And as long as the wind blows, and anywhere it blows, there will always be newer atmospheric mysteries to discover.
References:
- Hayes, J. M. (1998, July 20). Evolution of the atmosphere | History, Composition, Changes, & Facts. Encyclopedia Britannica. https://www.britannica.com/topic/evolution-of-the-atmosphere-1703862
- Earth’s Atmosphere: A Multi-layered Cake. (2019, October 16). Climate Change: Vital Signs of the Planet. https://climate.nasa.gov/news/2919/earths-atmosphere-a-multi-layered-cake/
- Montenegro, A. (2022, April 4). Longdom Publishing SL | Open Access Journals. Longdom. https://www.longdom.org/open-access/history-and-importance-of-atmospheric-science-90954.html
- Atmospheric Science – Planetary Sciences, Inc. (n.d.). https://planetary-science.org/planetary-science-3/atmospheric-science/
- Magazine, H. I. W., Dobrijevic, D., & O’Callaghan, J. (2021, April 30). 7 solar system worlds where the weather is crazy. Space.com. https://www.space.com/crazy-solar-system-world-weather
Image Courtesies:
- Featured image: https://bit.ly/3ZoQB7p
- Figure 1: https://bit.ly/3IUpBqP
- Figure 2: https://go.nasa.gov/3Iy6AsK
- Figure 3: https://bit.ly/3Ss4yz7
- Figure 4: https://bit.ly/3KDU3qA
