Fire Around 800,000 BCE, some of the H. erectus in East Africa decided to leave for

2.2.1 Fire Around 800,000 BCE, some of the H. erectus in East Africa decided to leave for

Asia and Europe. They alone among the great apes had lost the long body hair that covered all the mammals, so they had no insulation against the cold winds, rain, and snow. They left tropical forests and the savannah in East Africa and crossed desert regions to enter the temperate Near East, and then later turned to the frozen north of Asia and Europe in the middle of the Ice Age. Keeping warm with clothes and shelter was not important in tropical East Africa, but became critical in the frozen subarctic north. They may have huddled together to keep warm, and perhaps relied on the moon and stars to see at night.

The mastery of fire was not the invention of a new object that did not exist before, but the invention of methods to control it for our benefit. We have found evidence for H. erectus and fire in Zhoukoudian near Beijing (40 N) which is

59 thought to be from 460,000 years ago. The conquest of fire probably began with

2.2 ENERGY AND POWER

natural fires started by lightning or natural sparks. A person who learned to keep a reasonable distance from fire could use it to keep warm in a cold night, or to roast animal flesh to make it softer and easier to eat. The next achievement of mastery was to maintain fire at a steady level without extinguishing, by feeding it with wood or dung, sheltering it from wind and rain, and giving it oxygen by blowing on it. A fire also needed to be contained by barriers, and primitive humans learned to extinguish their fires with water or earth.

Most plant materials are primarily made of carbon and therefore make reason- ably good fuels, as long as they are dried and have plenty of surface area to contact with air. Air primarily consists of nitrogen (78%), which does not burn, but the less abundant oxygen (21%) does. When you burn a twig or a piece of straw, you are witnessing the following reaction, which produces carbon dioxide:

C þO 2 ) CO 2 þ energy

In this reaction, C is carbon, O is oxygen, and CO 2 is carbon dioxide. We see this energy in the form of radiating heat and light, hear the crackling sound, and feel the warmth.

The first fuels had to be locally available and dry—presumably grass, brush- wood, or branches. Massive logs are difficult to burn, as there is not much surface area and the interior is not exposed to oxygen. Dried animal dung from cattle, sheep, and camels contain undigested fibers and make good fuel. A longer burning torch can be made by soaking branches in animal fat, vegetable oil, or mineral pitch that seeped through the ground. Eventually, humans learned how to make charcoal by burning wood with insufficient air to drive off the volatile material and smoke, leaving only a core of concentrated carbon that would burn to produce a lot of heat but little smoke.

The next advancement in the mastery of fire was the ability to start a fire any- where at any time, so that one is not totally dependent on finding natural fire. The fire-starter needed a method to create a local temperature that was higher than the autoignition temperature of the fuel—about 230

C for dry grass or thin pieces of wood. Sulfur and yellow phosphorous have lower autoignition temperatures, which is why they are used in black gunpowder and in friction matches. The friction method of starting fires, familiar to Boy Scouts, involves rubbing two pieces of wood together till there is enough heat to raise the temperature and cause a fire to start. The spark-ignition method uses percussion to create a spark by hitting a piece of stone against another stone or metal. Iron pyrite is easy to find, but flint is even better. The spark is then directed to a pile of wood shavings or sawdust, and the small fire is encouraged by blowing. The modern cigarette lighter has a steel wheel against a flint to create a spark, and a wick soaked with butane to catch fire. Friction matches, based on powdered glass, sulfur, and phosphorus, were invented in the 1800s and served as miniature and portable fire-starters.

Combustion consumes oxygen, so a vigorous flame depresses the local oxygen level in the air. A good draft is required both to provide oxygen in fresh air and to remove smoke and combustion gases. Without enough fresh air, the chemical reaction changes to partial combustion, releasing less than a third of the heat of full

60 CHAPTER 2 INVENTIONS FOR WORK

combustion, and producing poisonous carbon monoxide. Moving a fire indoors pro- vides shelter from the wind and rain, but requires a chimney for necessary ventilation.

The conquest of fire was one of the most important milestones of human prog- ress and has been celebrated in the mythology of many races, usually as the magical gift of gods. In ancient Greece, the Titan Prometheus stole fire from the gods as a gift to men, and was punished for that crime; in Persia, Zoroaster represented the forces of good associated with heaven, light, and fire; in India, the fire god Agni presided over sacrifices. The warmth of fire was critical for the human conquest of the frozen north during the height of the ice age.

Fire also provided a gathering place where family members or tribesmen could socialize and eat in comfort, protected from the cold and dark. Cooking greatly expanded the range of available food beyond soft leaves, fruits, and soft choice meat. Rice and wheat are difficult to digest without cooking in water, and roasting softens tough meats and makes them chewable. Heat also destroys many germs and other disease causing microbes. Fire opened the way for humans to advance beyond the Stone Age, by making new materials of ceramics and metals, and manufacturing tools and weapons. Much later, when we mastered the steam engine and the internal combustion engine, fire and heat led to new sources of energy and power and brought us to the Industrial Revolution.

Many forests have been cut down for fuel around major cities, and around mining and manufacturing centers. Natural biomass has been unable to keep up with the demand from an expanding and more prosperous population. Because of this, the fossil fuels of coal, oil, and natural gas have come to be the dominant fuel since the Industrial Revolution. Outcrop coal was used in Britain during Roman times, but did not play an important role till the Middle Ages as long as the supply was limited to surface coal. Underground mining of coal featured prominently in the Tiangong Kaiwu published in 1637 in China. The Industrial Revolution in Brit- ain depended critically on coal mining.

Herodotus mentioned the use of asphalt in the construction of the walls and towers of Babylon, which came from oil seeping from underground. Naphtha or liq- uid oil was used in the Greek fire for warfare during the Byzantine Empire. Tiangong Kaiwu also mentioned the use of bamboo poles to conduct natural gas from wells, to create fire for the evaporation of brine to produce salt. Petroleum became an impor- tant source of energy after the development of drilled oil wells, which ensured a steady and growing supply. This was particularly spurred by the 1858 drilling of an oil well by Edwin Drake in Pennsylvania, which reached a depth of 21 m.