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(You are at Part 2 of The Energy Chain, if you would like to start at the beginning part, click here.)

Long ago, when the skies were clear and rush-hour traffic was not even a distant thunder, life was a bit simpler.
Or was it?

If you didn't get eaten by a wild animal by noon, you were probably fine until nearly freezing to death in a storm that evening while trying to return to your cave in the dark...

Thus was born humans first need for energy: light and heat.

In those days, fire came in two flavors: lightning strike or molten lava.

If you were lucky enough to be near a tree when lightning struck, you got fire.
If you were too close though...well, you get the picture.

A little later in time, humans actually figured out how to start a fire on demand.
This is where EROEI really first came into the picture.

In order to start a fire you needed kindling and firewood.
If you lived near a forest, there was plenty of fallen branches and twigs you could pick up. However, later when there were LOTS of people ALSO gathering branches and twigs for THEIR fires, the fallen twigs and branches soon became a rare commodity. Even though people also used dried animal dung (cow pies), straw, and sometimes dried peat, wood was the most common fuel for heating, lighting and cooking.

But humans soon developed stone and then bronze and iron cutting tools to easily cut down trees.
You would think that now the firewood issue would have been solved...but instead, it became more complex.

The problem had to do with AVAILABILITY of the fuel (in this case TREES), DEMAND (population), and DISTANCE (how FAR the trees were from the fireplaces they were needed).

To solve this problem, people would live NEAR to the source of the fuel, TREES.
This was fine when a few people were around. But, as the population increased and the one or two huts became a village, the fuel (TREES) started to run out.

Suddenly, people had two choices: MOVE to a new location that had more TREES or FIND a source of TREES and bring them TO the village.

Now, here is a perfect example of EROEI in action:

If the people moved their entire village to another forest, that would take A LOT of ENERGY! But, people reasoned that it would take LESS ENERGY to send one or a few or their population to ACQUIRE the TREES and then bring them back for use.

Thus the job of woodsman was born.

The woodsman's job was to FIND a source of TREES that was close enough and easy enough to transport the wood back to the village.

Here are the ENERGY COSTS of the woodsman:

TOOLS: Axes, saws, etc.

Energy was needed to MINE the iron to make the tools.
Energy was also used to fire the crucibles to melt the iron and work the tools.
Energy was used to make the ax handles.
Food was needed to feed the miners and the blacksmith making the tools.

Was the woodsman clothed?

Yes, well energy was used to make his clothes and feed the people who made the clothes, and who farmed the materials (and feed for the sheep too!).

Animal force was needed to GET TO the trees (ox cart, pack animals, simple wagon with horses).

Animals also required food and harnesses (tools).

Time and food was needed to travel TO the source of the trees (sandwiches didn't come cheap!).

PHYSICAL LABOR, FOOD and TIME ENERGY of the woodsman to chop down the trees. Time and animal energy was needed to bring the wood back to the village.

Some form of payment (food, grog, wench(!)) was needed to keep the woodsman happy -- which, of course, was an exchange of more forms of energy.

Besides firewood, many of the old oak forests were also cleared simply to make room for growing food for the increasing human population and feed for the increasing horse and animal population.

Firewood actually had to be imported from distant areas and brought to the towns (not villages anymore!) via wagons drawn by teams of horses, river barges, and sailing ships.

As the population increased, the demand for fuel (TREES) and agricultural land (FARMS) also increased. As the demand increased, so also did the COST in acquiring and transporting trees from afar.

But with the larger transportation vehicles also came another concept: ECONOMY OF SCALE.

A barge or sailing ship certainly took more energy to build and operate, but it could also carry a lot more trees than a single pack animal could...thus making this fuel (TREES) still affordable and accessible for most of the population.

So...the true ENERGY COST to use the fuel (TREES) got buried in the application of new technology.

This was not soon to last though.

The population in Europe continued to increase. Towns became cities full of people who needed to be fed and kept warm and trees became scarce.
Demand for fuel (TREES) was quickly outrunning the supply.

But by the 16th century mankind began turning its attention to another form of energy: COAL

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