00:00We now know that the answer to the question, why is life on Earth so varied, is actually the answer to the question, why is the DNA molecule itself so varied?
00:10What are the natural processes that cause the structure of DNA to change?
00:15Well, part of the answer, actually, doesn't lie on Earth at all.
00:20It lies up there amongst the stars.
00:22And I can show you what I mean using this, which is a cloud chamber, a piece of apparatus that has a unique place in the history of physics.
00:34I'm going to cool it down using dry ice, frozen carbon dioxide, just below minus 70 degrees Celsius.
00:41The cloud chamber works by having a super-saturated vapour of alcohol inside the chamber.
00:55Plenty on there.
00:57Now, I want to get that alcohol, I want to boil it off to get the vapour into the chamber.
01:02I mean, this is the first genuine particle physics detector.
01:06It's the piece of apparatus that first saw antimatter.
01:10And it really does consist only of a fish tank, some alcohol, a bit of paper and a hot water.
01:20There, look at that.
01:22You see that cloud, that vapour trail?
01:26That's a cosmic ray.
01:28That was initiated by a particle, probably a proton, that hit the Earth's atmosphere.
01:34It almost certainly originated outside our solar system and was accelerated by the magnetic fields of our galaxy.
01:42It may even have begun its life beyond our galaxy.
01:47Now, imagine if one of those hits the DNA of a living thing.
01:52What that will do is cause a mutation.
01:55That mutation may be detrimental or, very, very occasionally, it might be beneficial.
02:02And I think it's quite wonderful to imagine that maybe one of the key mutations that were selected for over the millennia
02:10that led to some trait in me was caused by some particle that began its life,
02:15perhaps in a massive supernova explosion, perhaps outside our galaxy,
02:20and went and hit the DNA of something and caused some kind of beneficial mutation.
