One-point-two kilograms per cubic meter. Why is this number significant? It’s the approximate average density, or mass per volume, of the air at sea level.
As you might expect, this mass pales in comparison to that of water, which is roughly 800 times denser than the atmosphere above it. Despite this, air has enough heft to ensure that high-speed hurricane winds can lift whole houses clean off the ground. And when pushed through a jet engine, it can hold a 640-ton airplane aloft — no mean feat for such a lightweight fluid.
Earth’s atmospheric density has fluctuated significantly over the course of its history. In fact, Earth had more in common with Venus, a thick, toxic hothouse world, billions of years ago, according to a study published in Science Advances in 2020. The surface of our blue planet was a molten magma ocean at the time, and its pre-life atmosphere consisted of a pinch of nitrogen and a pouring of heat-trapping carbon dioxide; truly a hell on Earth.
Thankfully, unlike Venus, our planet is farther from the sun. Eventually, the leftover heat from planetary formation was released from the system, and water oceans could develop. Despite our current CO2 emissions, it is unlikely that we’ll ever see a true return to Venusian form. But, still, the question remains: what would happen to life on Earth if the air suddenly got much, much soupier?
Double the Atmosphere, Double the Heat
To make this hypothetical scenario just a little breezier to calculate, let’s assume we were able to magically double the amount of gas suspended in the Earth’s atmosphere. That means twice as much nitrogen, oxygen, carbon dioxide, and everything else.
Read More: Changes in Earth’s Orbit Likely Kickstarted One of the Hottest Periods in History
While it is certainly true that our atmosphere is life-giving, protecting us from dangerous space radiation and insulating the planet, it is possible to have too much of a good thing. One of the first effects we’d notice is that it would be a lot hotter. Since the pressure of every gas would be doubled, we’d have twice as many greenhouse gasses just floating around.
While we don’t exactly know what those ramifications might look like across the globe, one of our closest parallels is a climate event known as the Paleocene-Eocene Thermal Maximum, or PETM. This interval of extreme warming lasted for 100,000 years during the late Paleocene and early Eocene eras, about 55 million years ago.
Scientists estimated that average PETM temperatures exceeded 90 degrees Fahrenheit, publishing their results in a 2022 study in Proceedings of the National Academy of Sciences. This represents a massive increase over the current average of 59 degrees. Concentrations of CO2 during this tumultuous period in Earth’s history were roughly double our present-day reading of roughly 420 parts per million.
While the PETM was caused by a variety of factors, possibly including changes in Earth’s orbit, the effects it wrought on the globe were consistent with a climate change nightmare scenario: rising sea levels, extreme weather events, and mass die-offs among sensitive organisms, particularly in marine environments.
Oxygen Overload
Of course, we mustn’t forget about the other gasses in the mix. We’d also be blessed (or cursed) with twice as much oxygen. This sounds wonderful in theory, but in practice is a little more complicated. An ancient analogue took place between 360 and 299 million years ago, during the Carboniferous period, when oxygen made up 35 percent of the atmosphere, compared to today’s 21 percent.
Read More: Earth's First Stable Dose of Oxygen Nearly Ended All Life
This resulted in two things: massive forest fires, and giant creepy-crawlies. With an increase in the supply of oxygen, it would have been much easier to commit arson in the Carboniferous. And thriving in these flammable forests were eight-foot-long millipedes and hawk-sized dragonfly relatives.
Since oxygen is a key component in an organism's metabolism, it was long assumed that the higher concentration is what allowed for these bigger bugs. However, another variable might be the relative lack of competition from vertebrates, which were just gaining prominence on land at the time. Regardless, you’d certainly feel a boost as each breath gave you twice as much energy in this new, denser air.
But be warned, you may also feel a tad intoxicated. We’d also be doubling the nitrogen, which has a narcotic effect at high pressures. Scuba divers, who pressurize their air in heavy tanks, are well-acquainted with the so-called "martini effect," also known as nitrogen narcosis. That's because descending 50 feet increases the nitrogen pressure of their air, such that the effect is equivalent to a dry martini, with the potential to induce mild impaired reasoning and a feeling of euphoria.
Living with a Heavy Atmosphere
Even the air itself being heavier would have major repercussions, too. In order to boil, a liquid must attain a pressure equal to that of the atmosphere itself. But with air twice as thick, cooking would become a surprisingly challenging endeavor, since water would need to reach 248 degrees Fahrenheit to become vapor, a 30-degree shift from normalcy. Plus, it could also trigger massive effects on weather systems, as the process of evaporation would be stalled.
Read More: We May Have Found a Super-Earth Planet With an Atmosphere
In addition to drier air, winds themselves would likely be slower but also more powerful — a bit like the currents of an ocean. The strength of a full-fledged storm might be off the charts.
Despite these challenging conditions, though, flight could paradoxically be easier. A report from the Federal Aviation Administration highlights a long-known reality for pilots: with increasing altitude comes decreasing air density, and decreased aircraft performance. A thinner atmosphere does mean less drag and turbulence, but it also equates to less lift and thrust, more than offsetting the benefits.
Commercial airliners fly so high to minimize drag and weather effects, but this new denser air might make their takeoffs and landings a little easier, allowing for lower speeds. And a soupier atmosphere could even allow for a long-maligned form of transportation to make a comeback: airships. While the hydrogen-fueled Hindenburg disaster left a poor taste in the public’s memory, doubling the atmospheric density also roughly doubles the lifting capacity of a balloon, in accordance with Archimedes’ principle of buoyancy.
The reality of life with an atmosphere that's doubled in density would surely have its fair share of challenges. But rest assured, the chance of this absurd change ever becoming reality is about as likely as pigs taking flight. Although who knows what’s possible under a heavier sky?
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Science Advances. Redox state of Earth’s magma ocean and its Venus-like early atmosphere.
Britannica. Paleocene-Eocene Thermal Maximum.
PNAS. Spatial patterns of climate change across the Paleocene–Eocene Thermal Maximum.
PNAS. Environmental and biotic controls on the evolutionary history of insect body size.
Federal Aviation Administration. Density Altitude.
Britannica. Archimedes’ principle.
