The Human Dimension
The reason we study the Earth system is because we live here, and are a part of it. Everything that happens to the Earth affects us as citizens of the planet, and everything humanity does has an impact on the rest of the system.
In its struggle to survive, humanity has rarely, if ever, existed in equilibrium with the rest of the Earth system. Man vs. nature has been a recurring theme throughout history and has honed the human skills of adaptation, assimilation and domination of the natural environment. The enormity of the planet and relatively small numbers of humans in early historic times lessened the global impact of hunter gatherer land management practices, though there is increasing evidence that people were making their mark on the global environment much earlier than previously assumed.
As organized societies emerged, so did the ability to extract natural resources for food, fuel and building materials. The need for raw materials exploded with the industrial revolution at the turn of the 18th century, and the results of poor resource management began to be felt regionally and even globally. Humanity began to make an indelible mark on the planet through increased consumption of fossil fuels, deforestation and agricultural land degradation, trends that continue today as Earth's human population exceeds 6.1 billion people.
Society has evolved to take advantage of the natural services that the Earth system provides - cities were settled in proximity to fresh water or navigable rivers and harbors. Fertile glacial soils were tilled, natural grasslands grazed by sheep and cattle, and forests cut for fuel and lumber. Oceans are harvested and mineral and fossil fuel reserves drilled and mined.