10 Fascinating Facts about Earth’s Atmosphere

We might take the air we breathe for granted, but the Earth’s atmosphere is a product of billions of years of finely tuned evolution.

Earth’s atmosphere is unique among all the planets and moons we know, both in our own solar system and in others light years away. It’s the product of 4.7 billion years of evolution, shaped by everything from its proximity to the Sun to the rise of photosynthetic life. Without our cherished atmosphere, our planet would be lifeless, baked by the scorching rays and radiation of the Sun during the day and frigidly cold during the night. One only needs to look to Mars to see what happens to a planet when most of its atmosphere gets lost to space over the aeons. In this week’s listicle, I’m going to be exploring some of the things that make the air we breathe so special.

#1. Earth Has Had Three Atmospheres

NASA

The second atmosphere formed during the Hadean Aeon around 4 billion years ago.

Today’s atmosphere consists of 78% nitrogen, 21% oxygen and traces of various other elements and compounds, including varying amounts of water vapour. During the Hadean Aeon, however, when our planet was young, the air was a product of the solar nebula that gave birth to the planets over 4.5 billion years ago. This fiery primordial world was ravaged by impact events and volcanism. Eventually, a combination of volcanic outgassing and impact events replaced the predominantly hydrogen-based atmosphere with nitrogen and carbon dioxide. By about 2.4 billion years ago, the third and current atmosphere started to form.

#2. Oxygen Caused the First Major Extinction

Christian Fischer

Cyanobacteria, commonly known as green algae, was responsible for the first major extinction event.

Until around 2.4 billion years ago, there wasn’t any oxygen in the atmosphere. Nonetheless, microscopic life was well-established, including photosynthesising cyanobacteria. Creating oxygen through photosynthesis, these organisms, which are responsible for creating green algae, transformed the planet’s atmosphere. Until the Great Oxygenation Event, oxygen had been trapped by water as it created rust from iron deposits, preventing it from being freed into the atmosphere. At the time, most life was anaerobic, for which oxygen can be toxic. Thus, while this event made the world habitable for us today, it also saw the Earth’s first mass extinction.

#3. Global Warming Was Once Much Greater

Wikimedia Commons

During the Cambrian Period, CO2 levels were 16 times higher than pre-industrial ones.

While mankind has presided over a 60% increase in CO2 levels since the dawn of the Industrial Revolution, the greenhouse effect has, throughout most of Earth’s history, been much stronger than it is today. During the Cambrian Period, which saw one of the biggest evolutionary radiations of all time, CO2 levels were 11 times higher than today. Consequently, the world was 7°C warmer, there was no ice at the poles and sea levels were much higher. Hundreds of millions of years later, during the time of the last dinosaurs, they were still almost 5 times higher than today. Eventually, however, the world cooled, hailing in the ongoing Quaternary ice age.

#4. The Sky Should Be Violet

Pixabay

The colour of the sky is due to a combination of scattering and our optical physiology.

The reason the sky is blue is down to a phenomenon called Rayleigh scattering, a term coined after the nineteenth-century British physicist who first explained it. The Sun’s light represents every colour of the visible spectrum, but colours with shorter wavelengths, such as blue and violet, are scattered by the atmosphere in such a way that they overpower those with longer wavelengths like red and orange. However, given that violet has the shortest wavelength of any colour, shouldn’t we all be seeing the sky as purple? The reason we see blue rather than purple is down to our physiology – the human eye is more sensitive to blue light than violet.

#5. The Atmosphere Extends 6,200 Miles into Space

NASA

The International Space Station orbits in the upper part of the thermosphere.

The Earth’s atmosphere consists of five layers. From the lowest to the highest, these are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The outermost layer extends from about 430 miles (700 km) above sea level to around 6,200 miles (10,000 km), where it finally gives way to the solar wind. The exosphere is still considered part of the atmosphere because the few gaseous particles within it are still gravitationally bound to Earth. However, some scientists consider the lower layer, the thermosphere, to be the highest layer of the atmosphere. The thermosphere is home to the International Space Station in Low Earth Orbit.

#6. Oxygen Levels Used to Be Much Higher

The Paleobear

The Carboniferous world saw the highest ever atmospheric oxygen levels.

Earth’s oxygen is a by-product of photosynthesis. With the absence of large plants, oxygen levels remained low even well after the Great Oxygenation Event. However, when life started colonising the land in the form of vast swamp forests during the Devonian Period, oxygen levels started to skyrocket. During the Carboniferous, around 300 million years ago, they reached their highest ever level of 32.5%. This was a result of nature spiralling out of control, leading to a volatile world where forest fires would have been rife, burning for days in the high-oxygen atmosphere and giving the sky a bruised reddish colour.

#7. Blood Boils After 60,000 Feet

NASA

Above 60,000 feet, you’ll need more than just an oxygen mask and warm clothes to protect yourself.

All terrestrial life on Earth has adapted to a comfortable air pressure equal to one atmosphere where water boils at a 100°C. As elevation increases, air pressures get lower as do boiling points. At the top of Mount Everest, some 29,000 feet up (9,000 m), water boils at 72°C. However, ascend to an elevation of around 60,000 feet (18,000 m), and you’ll reach the so-called Armstrong Limit, where the air pressure drops to a level that’s deadly without a pressurised suit. This is because, at this pressure, bodily fluids, such as saliva and blood, boil at the normal human body temperature of 37°C. Unsurprisingly, this typically means death within a minute.

#8. With Elevation, It Gets Hotter After Getting Colder

Pixabay

Atop the highest mountain on Earth, water boils at 72°C.

Everyone knows that its gets colder the higher you ascend, but the warmest temperatures are actually found in the thermosphere. The coldest region, by contrast, is found at the border between the mesosphere and thermosphere, some 62 miles (100 km) above sea level, where temperatures reach a frigid -100°C. However, the thermosphere sees by far the greatest temperature fluctuations of all, sometimes reaching a peak of 2,500°C, although it wouldn’t feel hot, due to the region being a near vacuum. The high temperatures are due to intense solar radiation, which would be deadly to life on Earth if it weren’t for our atmosphere.

#9. It Protects Us from Meteors

Pixabay

Earth’s atmosphere protects us from all sorts of space-borne hazards.

From lethal solar radiation to low pressures and extreme temperatures, our atmosphere serves as a protective blanket safeguarding us from the inhospitable expanse of the great beyond. Fortunately, the atmosphere also protects us from another type of disaster – impact events. Earth’s atmosphere burns up almost all the meteorites and space junk that encounter it. This is due to atmospheric friction burning up smaller objects in temperatures reaching 1,650°C. Of course, there are also objects that are too large or moving too fast for the atmosphere to burn up before they hit the surface, as the dinosaurs found out 66 million years ago. ☹

#10. There Is 40 Trillion Gallons of Water in the Sky

Pixabay

There’s enough water in the atmosphere to soak the whole planet in an inch of rain.

Of all the chemicals on Earth, water has the most profound implications for the evolution of life as we know it. Nothing on the planet can live without water, but it’s also the fact that our atmosphere and distance from the Sun helps to maintain a temperature around the triple point of water. This means that water can exist as a solid, liquid or gas. The atmosphere is home to an average of almost 40 trillion gallons (150 trillion litres) of water at any one time, which is enough to drown the entire planet in an inch (2.5cm) of rainwater. However, while it sounds like a lot, atmospheric water vapour only accounts for 0.001% of all the water on Earth.

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Do you have any other facts about the Earth’s atmosphere you’d like to share? If so, let me know in the comments below!

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