• Ashwini

GS16: The atmosphere.

Our atmosphere is a life-supporting blanket of air enveloping the Earth. It has been there since the formation of our planet, though not with the same property as it has today. It is very easy to veer in the horizontal direction, but should we move a mere 8000 meters above the surface of the Earth, we would suffocate. We can survive without food for a few weeks, or without water for a few days, but, without our atmosphere, we would not survive more than a few minutes. We are analogous to fish in the ocean of air. Good only till we are in it. The moment we are detached from it, it will be hard to survive a moment

Comet NEOWISE Brightens the Night- Image Credit: NASA

What would happen without an atmosphere?

Death, correct. But what else will happen? Without the atmosphere, there would be no lakes or oceans. There would be no sounds, no clouds, no red sunsets (you would have missed the aesthetic sunrise or sunsets). There will be no clouds to precipitate. The nights will be unbearably cold, and days will be scorched under the intense sunlight. Everything on the planet would be at the mercy of the sun beating down upon a planet utterly parched.

We have spent numerous hours on the planet, and still, plenty are left, but we have forgotten how precious this blanket of air is for our survivable. Even though the air is tasteless, odorless, and (most of the time) invisible-until it mixes with pollutants generated by us, it protects us from the scorching rays of the sun and provides us with a mixture of that allows life to burgeon. Since you are not able to see or smell the air, it may be possible that there could be trillions of the air molecules between your eyes and the screen on which you are reading this article. Some of these may have been in a cloud-only yesterday, or over another continent last week, or perhaps part of the life-giving breath of the person who lived hundreds of years ago.

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Our sun, which is an average-sized star situated near the edge of the milky way galaxy, primarily provides warmth for the planets. The distance between our sun and the earth is around 150 million km, and the Earth intercepts only a very small fraction of the Sun’s total energy output. However, it is the radiant energy that drives the atmospheric phenomenon on the surface and aloft and allows Earth to maintain an average surface temperature of about 15-degree C. You can experience scores of temperature on the surface of the Earth, as readings drop below -85 degrees C on the frigid Antarctica night, and rise to above 50 degrees C on the hot subtropical desert.

From Early to Modern Earth- Variation in Earth atmosphere.

It is hard to imagine that the early atmosphere lacked the essence of the modern-day atmosphere. The atmosphere that originally surrounded the planet was abundantly rich in Hydrogen and Helium- the two most abundant gases found in the universe- as well as hydrogen compounds in the reducing environment, such as methane and ammonia. These lighter gases with time escaped into space from Earth’s hot surface.

The second, more dense atmosphere, that enveloped that Earth was gases released from the volcanoes and steam vents (this process of release of gases from within the surface of the Earth is known as Outgassing). These gases are believed to have the same composition as we notice in recent eruption, mostly water vapor (about 80%), carbon dioxide (about 10%), and up to a few percent nitrogens.

As millions of years passed, the constant outpouring of the gases, mainly water vapor, into the atmosphere eventually transformed into the clouds. Also, a few scientists maintain that some of the water on the surface was brought down by the comets or meteorites coming from outer space. They also say that the nuclei to the evolution of life were also brought to the planet by these extraterrestrial objects. This theory is famously known as Panspermia.

When these clouds precipitated for thousands of years, they formed the river, lakes, and oceans of the world. The larger amount of carbon dioxide was engulfed in the ocean. Through chemical and biological processes much of the carbon dioxide became locked up in carbonate sedimentary rocks, such as limestone, which later metamorphosed to give rise to carbonate metamorphic rock-marbles, etc. With much of the water condensed into the water bodies, and carbon dioxide dissolved into the ocean; the atmosphere was dominated by molecular nitrogen, which is chemically inert.

By this time the earth has already prepared one of its abundant components i.e. nitrogen. The appearance of molecular oxygen initiated by the process of photodissociation, which was a rather slow process. During this process, the atmospheric water vapors are split into hydrogen and oxygen by the energetic rays from the sun. The hydrogen being lighter rose and mixed with outer space while the oxygen remained in the atmosphere. The preparation of the molecular oxygen was boosted by the advent of life on the Earth. The early life-the traces of which we get in the form of stromatolites-arose in the reducing environment and took the pain of transforming the atmosphere into the oxidizing one alike today. And the process of photosynthesis in addition to photodissociation led to the modern oxygen-rich atmosphere by 2.4 Ga (Ga=billion years ago).

Algal Stromatolite (Fawn Limestone, Semri Group, Vindhyana Supergroup)

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  • Earth orbits around the Sun in 365.25 days. 0.25 days add to form 1 day after 4 years resulting in the leap year.

  • Earth completes its rotation about its axis in 23.9 days, defining days and nights.

  • Earth's axis of rotation is 23.5 degrees inclined from the normal to the elliptical equatorial plane of planets, giving rise to the seasons on the planet.

  • On two days of the year- Equinoxes, both the hemisphere is equally illuminated by the Sun.

  • Whichever hemisphere is close to the Sun experiences summer, while the one away from the Sun experiences winter.

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