Why The Earth's Atmosphere Is So Important | Naked Science Season 5 Episode 3

Planet Earth is an oasis of life thanks to its protective cocoon of gas, the atmosphere. This blanket of air shapes everything on Earth, protecting, sustaining, carrying water, and shielding us from cosmic impacts and killer radiation. The atmosphere is divided into five distinctive layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer becomes less dense further from the surface. We live in the troposphere, where air is thickest and pressure is greatest, conditions perfectly matched to our bodies.

On August 16th, 1960, Colonel Joseph Kittinger embarked on a record-breaking journey to 20 miles high (mid-stratosphere) before jumping. This military mission was crucial for the Space Race, testing human endurance at high altitudes and low pressures, and trialing new technology. Despite a crucial fault in his pressure suit's glove, Kittinger continued his ascent to 102,800 feet. His freefall lasted 4 minutes and 36 seconds, reaching speeds of 614 mph before deploying his parachute. This mission provided invaluable data and highlighted the critical importance of our atmosphere.

Earth's atmosphere is remarkably unique in the solar system. While other planets like Uranus and Neptune have clouds of near-frozen gas, Mars and Mercury have had their atmospheres blasted away by the sun. Jupiter and Saturn are gas giants with no solid surface. Venus, Earth's twin in size and proximity, has an incredibly hostile atmosphere with pressures high enough to crush a nuclear submarine, temperatures hot enough to melt lead, and clouds of sulfuric acid. The mystery is why Earth didn't follow the same destructive path as Venus.

The Earth's first atmosphere formed 4.5 billion years ago from gases bubbling forth from its molten core. Earth's gravity held these gases, and its magnetic field protected it from the solar wind, unlike Mars. The early atmosphere was rich in carbon dioxide, a greenhouse gas that superheated Venus. Earth's fortunate escape from a Venus-like fate was a 'lucky accident': a colossal collision with a Mars-sized body created the moon and stripped away Earth's initial deadly atmosphere. This allowed a new atmosphere, primarily nitrogen, carbon dioxide, and water vapor, to form from volcanic eruptions and icy comet impacts.

For the first half of Earth's life, there was no oxygen in the atmosphere. Around 2.5 billion years ago, cyanobacteria, a humble microscopic organism, began producing oxygen through photosynthesis. As these microbes multiplied, oxygen accumulated in the air, transforming the planet in the Great Oxygenation Event. This oxygen first reacted with ocean iron, then with soil and rock, giving them a reddish hue. Once these minerals were saturated, oxygen gathered in the atmosphere, leading to the evolution of complex life forms and plants, which further contributed to oxygen production.

The atmosphere is in constant motion, driven by the sun's uneven heating of Earth's surface and atmosphere. This movement of hot and cold air regulates global temperatures, preventing the poles from being drastically colder and the equator from being much warmer. Without this atmospheric circulation, deserts would expand, and many cities would experience extreme winters. The planet's rotation twists air flows, forming hurricanes. Moist air rising creates electrically charged clouds, leading to lightning and eventually rain as water vapor condenses. This process carries almost 3,000 cubic miles of liquid in the air at any given moment, preventing vast lands from being bone dry.

Atmospheric rivers are newly discovered narrow channels of hurricane-force winds that stretch for thousands of miles, carrying vast amounts of water vapor from oceans to coasts. They provide almost half the annual rainfall for parts of the American Pacific Coast, but also cause violent flooding when they remain stagnant. Predicting these rivers is challenging due to limited data over oceans. Researchers hope robotic drone aircraft can measure air temperature, winds, and humidity to improve forecasts. The changes observed in atmospheric rivers suggest a broader shift in climate and atmosphere, with human activities dramatically increasing warming carbon dioxide. Natural air filters are becoming saturated, potentially leading to more dramatic temperature rises and widespread flooding.

Above the turbulent troposphere lie four distinct layers: the stratosphere, mesosphere, thermosphere, and exosphere, each separated by temperature changes. The air thins dramatically in these higher altitudes, presenting challenges for ascent. The weight of the air creates air pressure; at high altitudes, the pressure drops, causing effects like marshmallows expanding and bursting. Humans exposed to these conditions would face extreme cold, lack of pressure causing swelling, and eventually organ failure due to lack of oxygen. The atmosphere also protects us from deadly radiation, with the ozone layer in the stratosphere absorbing 99% of high-energy ultraviolet rays, preventing cancers and protecting materials like balloons.

The mesosphere acts as a crucial shield against cosmic impacts. Every year, over 18,000 meteorites are on a collision course with Earth. As they enter the atmosphere at thousands of miles per hour, the air in the mesosphere pushes back and compresses, heating up to over 30,000 degrees Fahrenheit. This friction and heat cause meteorites to burn, light up the sky (as 'shooting stars'), and often shatter into fragments. The atmosphere significantly reduces their speed and size, transforming potential house-sized impacts into golf ball-sized fragments that form small holes on impact. Without the atmosphere, Earth would be constantly bombarded by much larger space rocks.

While only astronauts travel through the superheated thermosphere and distant exosphere, scientists imagine how alien atmospheres on distant planets could support their own unique forms of life. On gas giants like Jupiter, with no solid surface, creatures might rely on buoyancy, like hydrogen-filled blimps, floating amidst the gaseous layers. On planets with denser atmospheres, larger and more complex creatures could take to the skies, supported by the thicker air for gliding and flight, as seen in concepts for planets like Titan. For now, Earth remains unique, with its precious atmosphere being the sole reason for life as we know it.