lived in caves and first set out to establish villages It also shows us the contribution of science mathemat ics and industry to our built environment As you read this book we hope you begin to appreciate the contribution of the invisible infrastructure to the quality of your life We learned a lot and had fun writing it and hope you enjoy reading
Water Water Every where here would be no life without water As we look up to the heavens and particularly toward our nearest neighbors the planets one of our first questions is usually Is there any water there For centuries the lines crisscrossing the surface of Mars that can be seen through a telescope were thought to be canals perhaps constructed by intelligent beings Sadly this turns out not to be true When a space craft landed on Mars recently and sent back signals that water may exist under the surface of the red planet astrophysicists scientists who study the com position of the universe were wildly excited It was the first evidence that life may exist outside of Earth The first clue that other forms of life exist some where in the universe will most likely be the exis tence of water the building block of life What Is Water Although water is a liquid it is a compound of two gases one part oxygen mixed with two parts hydro
gen If you look at a globe of Earth you will notice that the color blue predominates Blue is typically used to designate water which covers 71 percent of the globe This ocean water tastes salty and contains as many as 32 different salts and minerals If you were to drink it you would get sick Actually too much saltwater could easily kill you On the other hand if you were to put a fish from the ocean into fresh water it would swell up by a process called endosmosis and die Fortunately for us seawater is heated by the sun and evaporates leaving all the salts and minerals behind It then condenses into clouds that float around the sky and through precipitation release their water as rain or snow Figure 1 1 When rain or snow falls on the land it seeps into the ground and forms springs rivers and lakes that all eventually flow back into the ocean The water that we use comes from these springs rivers or lakes and is relatively pure This cycle of evaporation conden sation precipitation seepage and flow is the natural water cycle without which life on Earth would not be
a to I TT I EVAPORATION f RAIN RIVER OCEAN LAKE t FRESH GROUND WATER Figure 1 1 The First People Even the earliest humanlike creatures called Aus tralopithecines who lived 4 000 000 years ago knew how and where to find water When our human ancestors first left their cave dwellings more than 10 000 years ago at the end of the Ice Age or Pale olithic period they gathered in villages located near streams rivers or lakes They recognized that water was their most important commodity After all about 70 percent actually somewhere between 67 and 78 percent of the human body consists of water that must constantly be replaced Water in the body is used to help drive the digestive system to lubricate the body's joints to cushion the internal organs to cleanse the body both inside and out and to control the skin's temperature through evaporation as we perspire Our ancestors usually sited their dwellings close to water From their round huts of woven vines or
