In this chapter we start with the atmosphere, since the sunlight arriving at the planet's surface is influenced by it, and thus climate and winds. The main current systems in the oceans arise from winds blowing over the water's surface. See also wind and waves Where such winds blow for prolonged periods and with sufficient force, the ocean's water will be moved at speeds between 0.5 and 2 km/hr, contributing directly to the heat transport towards the poles. Much of the climate depends on these currents, which in tur n , depend on the climate. Both the weather and the ocean currents are therefore in constant oscillation or instability. One of these is the El Nino climate/current cycle that influences rainfall and drought far afield and which will be treated in detail in its own chapter. Also ocean productivity depends largely on upwellings caused by ocean currents. More of that in the chapter on plankton and how to feed the world. Ultimately, the health and physics of the oceans, plays an important role in the way our pl anet will warm in response to the burning of fossil fuels. That too, will have its own chapter.Because the circulation of water and air depend on the amount of heat arriving at the planet's surface, it is important to understand what ha ppens to the sunlight from the moment it enters our atmosphere. This simple picture helps to relate the relative distances involved. If the planet were the size of a billiard ball, say 5 cm across, then the whole surface of the planet, from Mt. Everest to the deepest ocean trough (20 km) would be no thicker than a human hair. Here is where everything happens to life (the biosphere). Within this human hair, there are at least two layers in the atmosphere and two in the ocean that move almost independently o f one another. \line At a distance of 150-300 km, the atmosphere is so thin that spacecraft can orbit there in low orbit. The geostationary satellites orbit some 36000 km higher, a distance of about six times the radius of Earth. The at mosphere is a blanket of protective gases providing insulation against otherwise extreme alterations in temperature. Earth's gravity pulls the gases towards its surface where the pressure is 1 bar, decreasing rapidly with height. At 100 km height, the pre s sure is only one millionth. About 80% of the atmosphere is found in the first 15 km; half in the first 5 km. In the diagram, the various zones are shown. Note that their boundaries vary appreciably from pole to equator and from day to night. The outer zon e is the exozone which gradually fades into space. At 600 km the pressure is a mere 1E-38 bar or less than a trillionth of a trillionth of a trillionth of surface pressure. Only the fastest atoms of the lightest gases, Hydrogen and Helium are found here. Close to the surface, the troposphere (between 8 km at the poles and 15 km at the equator) is where the weather and climate reign. It contains 85% of the atmospheric mass. Air temperature falls steadily at about 4-8\'baC for every km height, 8\'baC at the tropics and almost nil at the North Pole in winter. Where the passenger airliners fly, 10 km, the temperature is -60 degrees, varying with day and night and other conditions. Near the surface of Earth, the temperature is on average 15 degrees and the air is composed of 78% nitrogen, 21% oxygen and 1% argon. The tropopause is a region where the temperature starts to rise again, forming the boundary with the stratosphere, which extends upward to 50 km. Here is where protective ozone is found (20-50 km). The stratosphere absorbs ultraviolet light, which warms it. Just above the ozone layer, the temperature drops again gradually to -80 degrees at the mesopause. In the ionosphere, air particles are electrically charged by the sun's radiation, being able to move at high speeds in the almost perfect vacuum. The temperatures shown in the diagram, therefore have little meaning. A space craft in this zone would not experience it. Four electrically charged layers are found here, the D, E, F1 and F2 layers. These are c a pable of bouncing radio waves of various frequencies, enabling radio transmitters to beam their programmes much further. Short-wave radio frequencies are able to reach the other side of the planet under favourable conditions. Medium wave (MW) transmission s benefit from the D layer, which becomes active in the night. Polar auroras occur between 65 and 965 km height in the polar regions. Meteors from outer space burn up in the lower ionosphere, at around 100-150 km height.