Listen to part of the lecture in a class on earth science.
We've been talking about some of the affects that the human beings so act on the earth. One that you may be not aware of is that we've actually begun to change the length of the day. The other we say that one day is the amount of time the earth need to spin completely around on axis. And the imagery line runs through the center of the earth from the north to south. And of course there are a lot of physical causes they can affect the spin of the earth rotation but there is only one that can direct result of the human activity. Since 1950, human beings have built about ten thousand of artificial reservoirs all over the world. These reservoirs have redistributed tremendous amount of the earth water. When they are used to be in the area near the equator and the imagery line on surround the middle of the earth is now reservoirs in the areas of different latitudes. The latitude matters because, well, think of the earth and its axis. The equator contains the areas on the earth that are farthest way from axis, so water has been redistributed from equator? Reasons, then whatever the water is, it's close to the earth axis. It's like when ice skaters perform spins, when those skaters put their arms enclose to their bodies, they spin faster. So the earth is spinning faster because the reservoirs have redistributed the water closer to its axis. And because the earth spinning fast, since 1950 the length of the day has decreased by about 8 millionth of a seconds. I know that doesn't sound much, but the significant in that this is the first time that human beings ever had miserable affected on the earth motion.