Geoscience Reference
In-Depth Information
1.3 Pre-modern Organic Vegetable Economies
At the end of the 18th century three were the main economic sources of energy;
corresponding to three different kinds of biomass. According to the age of the
discovery and exploitation of these three sources, three ages can be distinguished in
the distant past (that is in the First epoch identi
ed in Sect.
1.2.3
). The original
source was food, the second was
rewood and the third was fodder for working
animals. A relatively small contribution came from two other carriers: falling water,
the potential energy of which was exploited by watermills; and wind, utilized both
by sailboats, and, much later, mills.
1.3.1 The First Age: Food
Since the birth of the human species some 5
7 million years ago, and then for some
-
85
90 % of human history, food was the only source of energy. In this long period,
the only transformation of matter in order to engender movement and heat was the
metabolism of organic material either produced spontaneously by plants and veg-
etation or converted into meat by some other animal consumed by humans as food.
Although nothing certain can be said about energy consumption per head at that
time, given the stature and physical structure of these early humans, consumption
per day of about 2,000 Cal could be plausible. Their own body was the early
machine used by humans. An animal body is not very ef
-
cient in the conversion of
energy. Only 15
400 Cal, is transformed
into work, while the rest is utilized in order to support the metabolism and dispersed
in the environment as heat and waste. The economic output of these far ancestors
consisted in collecting, transporting and consuming this original input of energy.
-
20 % of the input of energy, that is 300
-
1.3.2 The Second Age: Fire
re has been the main conquest in the history of energy.
7
The
The use of
rst
evidence of
re being used by humans refers to several different regions of the
world and can be dated between 1 million and 500,000 years ago. Fire was a
conquest of independent groups of humans in several parts of the world and the
main source of energy for several millennia. Its use spread slowly. In this case, as in
the case of food, an estimate of the level of energy consumption by our distant
ancestors can only be speculative. As far as is known for much more recent ages,
the level of
rewood consumption in different regions in pre-modern times may
have varied from 1 kg per head per day to 10 in cold climates, that is between
7
On the discovery of
re see particularly Perl
รจ
s(
1977
) and Goudsblom (
1992
).
