Dave – They're not sure but they think its to do with the centre of the Earth being a liquid metal ball and you get convection currents in that. There's a strange thing where it excites itself and turns itself into a dynamo, you get electric currents which make an electro magnet and that's what they reckon is making the magnetic field.

Chris – The field does flip from time to time doesn't it? I think the average is about every 100, 000 years, but in fact its less than that.

Dave – Yes, they reckon we're due for one fairly soon as the Earth's magnetic field is getting weaker very fast.

Chris – So does the North pole become the South Pole?

Dave – Yes.

There's convection currents going on inside the water – if you've got something warm its less dense so it rises upwards and the cooler stuff sinks and this creates a turning circulation. If you put that in the freezer, because the water is stirred up by the heat, the water will start moving and it will carry on moving for quite some time and this will keep mixing the water enabling it after its cooled down to keep loosing heat more quickly than cold water because that's more static and doesn't move so much to start with. Therefore the cold water will be overtaken on the freezing process, possibly by the hot water.

The obvious thing would be that the cold water would freeze first, because its got less energy to loose but I have heard that the hot water would freeze sooner but I've not looked in to it in detail.

The convection currents helping the water water freeze first make sense though. The other thing is if you heat up water and boil it you drive off all the gases dissolved in it and those gases might be reducing the freezing point. So if you did the experiment fairly and used distilled water or something it could be an accurate way of testing.

Its to do with the weather as planes all run on the same fuel, called kerosene which has carbon and hydrogen in it. When you burn it the fuel the hydrogen combines with oxygen in the air to form water, which then condenses to form long, thin clouds that you see. If the plane is flying through a particularly dry piece of air those water droplets will evaporate quite quickly, if its flying through air which is already quite damp then the water can't evaporate and the clouds last for ages.

The shuttle is just burning hydrogen and oxygen which produces water and then a cloud similar to the way an aeroplane does. If the light caught it correctly as time went by, or it might not have even condensed properly for a while and then the light caught it, hence the glow a while later.

 Its called the Maillard reaction after a French chemist Louis Camille Maillard. This is a chemical reaction between carbohydrate groups (that's sugars largely) and protein or amino-acids (those are the building blocks of proteins). It takes place at around 148 degrees and when these sugar groups lock on to the amino-acid groups they form these nice, brown caramelised substances which taste great – that's the nice aroma you get from cooking. As it happens at 148 degrees – that's 48 degrees hotter than water boils at – that's why you get a very different consistency and taste and texture to fried food compared to boiled.

Yes it is true, you get two copies of every gene; one from mum and one from dad. If you have two duff copies of this gene then you'll have quite serious thalassemia. If you have only one duff copy then it could actually protect you from blood parasites like malaria. It makes the red cell inhospitable so nothing can grow in there. Malaria as a parasite will be optimized to live in a certain type of cell and cellular environment, so if you change that by having different chemicals in there because the gene is slightly different the result is you will end up with a less hospitable home for the parasite to grow and as a result it doesn't grow so well.