Water

Water doesn't follow the normal rules of chemistry. For a start, it shouldn't really be a liquid on our planet. A water molecule is made from two very light atoms, Hydrogen and oxygen. And at the temperatures and pressures on the surface of the Earth, rules of chemistry say that water should be a gas. And, unlike any other chemical, when water freezes it expands. And so ice floats on water. Now you see this every day, but take a moment to think about how weird that is. Over time, this odd behavior has been very useful. By insulating the water underneath, floating ice has enabled complex life to survive and evolve on our planet, despite the many ice ages that have frozen the Earth's surface solid. And the strangeness just goes on and on. Did you know that hot water freezes faster than cold? Yes, really. No-one knows why. Water molecules can float upwards, against the force of gravity. That's because they love to stick to each other. They're so good at it that they can actually pull each other up through tiny channels, such as the tiny blood vessels in your body. That's how oxygen and nutrients reach the edges of your brain. The same process, called capillary action, allows plants to move water from deep below the ground to nourish the leaves and branches that grow in the sunshine.