Hey nose and/or mouth-breathers, Trace here for DNews. There's a question going around

Reddit Science right now that caught my eye: Where did Earth's atmosphere come from? And

we started talking about it, and we weren't sure either… "atmosphere" literally means,

"sphere of air," but "air" isn't really right either -- because that's just what we have

on earth. Venus and Titan have atmospheres, in that gases permanently cover their surface;

in fact, a number of the bodies in our solar system have atmospheres -- even the Sun. The

gases surrounding the celestial bodies are held, suspended in space by the gravity of

their host planets, which determines a lot about their makeup and potential to support

human life.

Our atmosphere came into being not long after the Earth cooled 4.6 billion years ago. As

hydrogen and helium are extremely prevalent in the universe chances are our atmosphere

contained them too, early on. The sun is 98 percent helium and hydrogen... However, as

we were so close to the sun and pretty hot ourselves, much of those lighter, faster-moving

elements escaped Earth's gravity. Jupiter, Saturn and Uranus got to keep theirs because

they were so far away, and so much more massive.

Scientists believe as radioactive elements decayed and the Earth cooled, our remaining

elements coalesced into solids, liquids and gases. A 2009 paper published in the journal

Science says, at this point, the Earth was hit by many, many comets and meteors -- bringing

water vapor, krypton, xenon and other atmospheric materials. Another, older, theory states it

was volcanoes that spewed water vapor into the sky. We'll leave it up to the researchers,

but needless to say, at this point we know there was water vapor, carbon dioxide, ammonia,

methane, and neon that they think was already swirling over our hot crust. And yet ANOTHER

theory proposes that 4.5 billion years ago, when the proto-earth was getting hit by asteroids

including a GIANT one that formed the moon, the neon in our atmosphere was BLOWN OFF and

a beneficial ratio of gasses were left behind.

From there, a secondary atmosphere began to form from those volcanic blasts and the leftover

heat inside the planet. Heavier elements like nitrogen split out forming 78% of our atmosphere

today as well as the carbon dioxide and water… As the planet cooled … life began to form

and they did the rest.

2.7 billion years ago, when the first primitive life forms began to form, they lived anaerobically,

or without air. These extremophiles digested sulfates for energy! Completely ignoring the

atmosphere. Later, cyanobacteria or blue-green algae evolved to suck in carbon dioxide and

output oxygen using photosynthesis. These guys are still around today. They use the

energy from the sun, and carbon dioxide to produce oxygen.

Eventually, and scientists know it happened, but are unclear HOW, there was so much oxygen

in our air, that it poisoned organisms that couldn't process it, causing a mass extinction.

Microorganisms that COULD burn O2 survived as did the cyanobacteria and over millions

of years, they added enough O2 to support the evolution of oxygen-sucking animals, which

evolved into the living animals today like you and me.

As the planet continued to cool, the water vapor began to rain down, dissolving the CO2

gases into it. The oceans were formed in this way, and the cyanobacteria spread creating

more oxygen. Oxygen is hard to find on most planets because it tends to react with everything.

It rusts metals, it burns easily, it can make water. So how it got to the balance of 21-percent

that we have today is still being studied. By final count, according to HowStuffWorks.com,

our air is "78 percent nitrogen, 21 percent oxygen, 0.9 percent argon and 0.03 percent

carbon dioxide. The remaining 0.07 percent consists of water vapor, hydrogen, ozone,

neon, helium, krypton and xenon."

*breathes* and it's pretty nice.

Do you have other science questions? Ask 'em! We're always in the market for new topics.

You can post your questions here in the comments or tweet them at us at-DNews! And if you're

loving the space stuff, come join us on July 30th at 4pm Pacific for our SpaceOut! This

month we're hosting NASA scientists who work with the Mars rover Curiosity! We're going

to hang out for a whole hour asking questions and digging into what they've been doing on

Mars for the last year. RSVP with this link to join! July 30th at 4pm Pacific Time. Thanks

for tuning in to DNews, please subscribe. [a]