I all way wonder why we can't breath in space and is it because there is no trees.
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The thing you need to understand is that the universe as a whole is a very, very empty place. Most of space consists of a vacuum far, far better than the best vacuum we can make here on earth, even with the best vacuum pumps (the sort they use for the particle accelerators at CERN, for example).
So the strange thing really is not that we can't breathe in space - which is perfectly natural, because you might have to travel miles to the nearest oxygen molecule, let alone enough to live on - but that we can breathe here on earth. So why is that?
There are multiple special reasons why we can breathe on earth, and they all need to come together for it to happen. First, the earth has be big enough (strictly, massive enough) to hold on to an atmosphere. It does that by means of gravity. All the molecules of the atmosphere are pulled down towards the centre of the earth, just as you are when you stand on the ground. The earth pulls its gas molecules hard enough to keep hold of most of them, unlike Mars, for example, which has lost most of its.
Second, there has to be oxygen in the make-up of the earth. That, as it happens, isn't a problem. All the water in the oceans is mainly oxygen, and a lot of the rocks under our feet are largely oxygen too.
Third, that oxygen has to be set free in the air. Locked into water or rocks it doesn't help us to breathe. That's where the trees come in. Over billions of years, they made the energy they needed to live by photosynthesis, a process which (among other effects) releases oxygen from the carbon dioxide in the air. Most of that oxygen would be trapped again when the plants (not just trees, but all green plants) died - but some wouldn't, because the plants, instead of being fully recycled, got turned into oil or natural gas which got trapped in the rocks underground. So really, the oxygen we breathe is pollution caused by trees, and the 'natural' state of the earth's atmosphere is to be high in carbon dioxide and very low on oxygen.
So the strange thing really is not that we can't breathe in space - which is perfectly natural, because you might have to travel miles to the nearest oxygen molecule, let alone enough to live on - but that we can breathe here on earth. So why is that?
There are multiple special reasons why we can breathe on earth, and they all need to come together for it to happen. First, the earth has be big enough (strictly, massive enough) to hold on to an atmosphere. It does that by means of gravity. All the molecules of the atmosphere are pulled down towards the centre of the earth, just as you are when you stand on the ground. The earth pulls its gas molecules hard enough to keep hold of most of them, unlike Mars, for example, which has lost most of its.
Second, there has to be oxygen in the make-up of the earth. That, as it happens, isn't a problem. All the water in the oceans is mainly oxygen, and a lot of the rocks under our feet are largely oxygen too.
Third, that oxygen has to be set free in the air. Locked into water or rocks it doesn't help us to breathe. That's where the trees come in. Over billions of years, they made the energy they needed to live by photosynthesis, a process which (among other effects) releases oxygen from the carbon dioxide in the air. Most of that oxygen would be trapped again when the plants (not just trees, but all green plants) died - but some wouldn't, because the plants, instead of being fully recycled, got turned into oil or natural gas which got trapped in the rocks underground. So really, the oxygen we breathe is pollution caused by trees, and the 'natural' state of the earth's atmosphere is to be high in carbon dioxide and very low on oxygen.