 Our rocky planet Earth is wrapped up in a gaseous blanket known as the atmosphere. It's the atmosphere that we can thank for all life on Earth. In fact, it's the only planet in our solar system with an atmosphere that can sustain life and is composed of a mixture of different molecules including mostly nitrogen, the oxygen that we breathe, argon and then carbon dioxide and other molecules in tiny concentrations including water vapor. As well as providing us with the air we breathe, the atmosphere also protects us from the radiation and the heat of our sun. By day, the atmosphere stops us getting too hot and by night it wraps us up in a blanket to stop us getting too cold. It also provides us with all our weather, oxygen to breathe, water vapor, weather and temperature control. I hope you're starting to see how wonderfully important this blanket of gas is to us. The atmosphere is about 100 kilometres thick and is broken down into different layers. It starts with the troposphere closest to the Earth which extends to 14.5 kilometres. Thanks to gravity this is the most dense part and is where the clouds are found. Nearly all of our weather happens in here. Then the stratosphere up to 50 kilometres which contains the very important ozone layer. The ozone layer both heat the stratosphere and also absorbs and scatters harmful ultraviolet radiation from the sun protecting all life on Earth. And beyond that we have the mesosphere up to 85 kilometres. The mesosphere protects us from flying pieces of space rock called meteors. When they hit the mesosphere the friction of the air causes most of them to burn up or at the very least to break down into much, much smaller pieces. Then there's the thermosphere. The International Space Station orbits the Earth at 400 kilometres. And then the exosphere is where our atmosphere merges into outer space. Another wonderful thing the atmosphere does is that it enables us to hear each other, to hear bird songs, to hear cars as we cross the road. Sound waves need air to travel as there is no air in space. Sound can't travel so space is silent. Any movies where space ships leave our atmosphere and explode, that noise is all fake. You wouldn't actually hear a thing. As well as sound we also have the atmosphere to thank for our sky being blue. Why do you think our sky is blue but space is black? Pause the video and have a think. The white light from our sun hits the molecules in our atmosphere which cause the blue light to scatter off in all directions giving our blue coloured sky. The blue light in particular scatters because it has the shortest wavelength and so is interfered with by the molecules in the Earth's atmosphere much more than the other wavelengths. The moon has no atmosphere and so the sky is black day and night because there is no particles to cause the blue light rays to scatter. That's why all photographs of the Apollo moon landings always have a dark sky. So we've seen some of the many reasons why the atmosphere is so fundamentally important for life on Earth. We're going to finish with a quick look at variation in atmospheric pressure. The pressure of the air is related to the weight of the air above. As we increase altitude so distance from the Earth there is still air above us but there becomes less air as we go further away from the Earth. So air pressure decreases as we increase altitude until we get to the edge of the atmosphere where there is no more air and so there is no pressure. Most of the atmosphere's molecules are close to the Earth's surface thanks to gravity. And so the air pressure decreases rapidly at first as we increase altitude and then more slowly at higher levels. This is why the air in the mountains is thinner and sometimes mountain climbers need oxygen to breathe. In fact the pressure at the top of Mount Everest is less than 30% of the pressure at sea level. So there we have the many reasons why the atmosphere is so important and why the atmospheric pressure is highest at sea level and decreases with altitude.