The Civilization Record
Energy
Humans began with their own muscle power and became a species able to draw on the planet's energy stores.
For the first humans the basic energy source of life was their own bodies. Fire, wood and, in time, domesticated animals widened that limit. Water and wind began to do mechanical work in a person's place. Coal and oil then opened a completely different scale of energy use.
Fossil fuels made energy that had accumulated underground over millions of years usable in a short time. Machines, factories, transport and electricity grids carried that energy everywhere.
So the productive capacity of civilisation grew steadily independent of the physical strength of human bodies. Today many times the energy a person spends directly is used on their behalf by machines and energy systems. One way to grasp the scale of civilisation is this: as much as how many of us there are, how much energy each person runs behind them.
Worth knowing
A modern person commands the power of 50-100 'energy slaves': the energy that supports them equals the continuous physical labour of that many people.
Fossil fuel overtook biomass (wood) as the primary energy source around 1900.
A year of fossil-fuel use carries energy equal to 400 years of net primary production of all current land vegetation.
Humanity uses about one ten-thousandth of the solar energy reaching the planet.