Could people breathe the air on Mars?

Let's suppose you were an astronaut who just landed on the planet Mars.

What would you need to survive?

For starters, here's a short list: Water, food, shelter — and oxygen

Oxygen is in the air we breathe here on Earth. Plants and some kinds of bacteria provide it for us.

But oxygen is not the only gas in the Earth's atmosphere. It's not even the most abundant. 

In fact, only 21% of our air is made up of oxygen.

Almost all the rest is nitrogen — about 78%.

Now you might be wondering: If there is more nitrogen in the air, why do we breathe in oxygen?

Here's how it works: Technically, when you breathe in, you take in everything that's in the atmosphere.

But your body uses only the oxygen; you get rid of the rest when you exhale.

The air on Mars

The Martian atmosphere is thin — its volume is only 1% of the Earth's atmosphere. To put it another way, there's 99% less air on Mars than on Earth.

That's partly because Mars is about half the size of Earth. Its gravity isn't strong enough to keep atmospheric gases from escaping into space.

And the most abundant gas in that thin air is carbon dioxide. For people on Earth, it is a toxic gas in high concentrations.

Fortunately, it makes up far less than 1% of our atmosphere. But on Mars, carbon dioxide is 96% of the air!

Meanwhile, Mars has almost no oxygen; it's only one-tenth of 1% of the air, not nearly enough for humans to survive.

If you tried to breathe on the surface of Mars without your spacesuit supplying your oxygen you would die in an instant.

You will suffocate, and because of the low atmospheric pressure, your blood will boil at about the same time.