After all, we live in a sea of free oxygen without damage.

There's not much free oxygen at the bottom of the sea.

Free oxygen has been an important part of the atmosphere ever since.

Go a little farther back and find no free oxygen at all.

For instance, there almost certainly was no free oxygen in the atmosphere.

For the first two billion years of life on Earth, the atmosphere contained little free oxygen.

Once the free oxygen is gone, many aquatic animals die.

Flesh does not have the free oxygen necessary for Thread life.

We don't know how there can be any measurable amount of free oxygen.

Along with the planet's complete lack of free oxygen, or even a magnetic field.

Moving up to today our atmosphere's construction has changed. there is now plenty of free oxygen.

The engine room was filling with free oxygen and hydrogen.

Free oxygen gas was almost nonexistent in Earth's atmosphere more than 3 billion years ago.

There are substantial quantities of free oxygen in the atmosphere.

They were the first organisms to make free oxygen by photosynthesis.

But nothing like animals, because there's no free oxygen.

The excess free oxygen started to accumulate in the atmosphere.

Living, active, occurring, or existing in the absence of free oxygen.

There would be no free oxygen in the atmosphere even today were it not for photosynthesis.

Appreciable concentrations of free oxygen were probably not present until about 2.5 billion years ago.

Local tissues can then pick up the free oxygen.

Not one trace of free oxygen, the breath of human life.

Originally, the Earth's atmosphere had almost no free oxygen.

Free oxygen was a sure sign of life—life that couldn't be so terribly dissimilar to his own.

The Archean atmosphere is thought to have nearly lacked free oxygen.