Environmental Engineering Reference
In-Depth Information
converts only 0.3 per cent of the sunlight energy that strikes its leaves into biomass, while
modern strains have conversion rates ten times higher.
Agriculture allowed humans to maintain a relatively stable environment, thus ensuring a
more predictable future. It was this predictability that allowed us to develop complex social
structures and culture. The reduced daily pressure to secure food allowed humans to devote
time to other pursuits: the refinement of tools and language, the construction of more
permanent settlements, and the development of complex social relationships. In this way,
agriculture is the most essential of all cultural achievements. Were we to try and express
this in an equation to rival Einstein's, we might say that E + T = C, or energy (through an
abundant food source) plus time (through the predictability of that energy source) begets
culture.
Playing with Fire
For millennia, wood, dung and crop residues were the main fuel sources for heating and
cooking. Indeed, these are still important domestic fuels in many countries. Fire was, of
course, used not only for cooking and heating but also as a source of light. Oil lamps
(burning animal and vegetable fats) have been used since the Paleolithic age (up to 40,000
years ago), while the more practical and versatile candle, using plant and animal waxes,
was developed about 2,000 years ago. These remained the principal method of lighting
One of the main reasons wood was eventually replaced as a major fuel was its value for
other applications, particularly as a building material and as the raw material for charcoal.
Wood is made of lignin, which consists of carbon, hydrogen and oxygen. By superheating
the wood, we can remove the hydrogen and oxygen atoms in the form of water (H
2
O),
leaving pure carbon. This is a vastly accelerated replication of what happens in the earth
when coal is formed, hence the name of this by-product: charcoal. The ability to make
charcoal was developed about 5,000 years ago. The importance of this discovery is that it
provided a fuel with a greater energy density than wood. Charcoal also produces far less
smoke, so it is well suited for indoor cooking. But by far its most significant application
was in the smelting of metals, which opened the way for vastly more effective tools and
weapons.
From Human Power to Horsepower
The desire for a more stable source of food led humans to domesticate wild animals; sheep
and goats initially, followed by pigs, oxen and chickens. Humankind also realised that it
could take advantage of certain animals' superior strength to pull sledges, ploughs and
