oxygen

[einsteinsdog]

Where has all our oxygen come from? There is little evidence of oxygen on othere planets , so something unusual must have happened on our planet

[jenstar]

Yes, a little something called photosynthesis!

[jake-the-peg]

To expand a little the vast majority of oxygen on the planet is believed to have been formed by living orgamisms - especially blue-green algae.

Life started very early in the Earth's history but for most of it was pretty basic you can generate a lot of oxygen in billions of years.

I'm assuming you mean 'free oxygen' as there is plenty of carbon dioxide and other oxides on other planets and carbon dioxide is of course a raw material for photosynthesis

[CT]

It's not really that there is less oxygen elsewhere, it's just that it is in other forms. On Venus, much of it is locked up in Carbon Dioxide and other substances.

[bigveg]

in the beginning(probably), there was a big mist of the simplest atoms, namely hydrogen and helium. because each atom has its own gravity, the mist became denser and denser until huge balls of it formed. the pressure was so intense in these balls that the hydrogen and helium atoms began to react and created stars. in the hearts of these stars were conditions suitable for nuclear fusion, thus creating all heavier elements that exist today. (know the moby song we are all made from stars??) if you want to be pedantic, yes some scientists are able to "make" other elements that dont occur naturally, but these are negligble in quantity, and rarely exist for more than a fraction of a second. oxygen does exist on other planets, though mostly in metal oxides (mars appears red becuase of iron oxides, or rust in the rocks). comets are often partly made of ice. on our planet, however, it is also in the atmosphere.