The carbon cycle and its alteration by human activities have become a major scientific concern over the last decade. Carbon is an element that is essential to life, and it cycles through Earth's spheres via processes such as respiration, decomposition, and combustion. Plants use carbon dioxide (CO2) from the air to build organic carbon, which then travels up the food chain as plants are eaten. In this sense, carbon is a building block of every plant and animal on the planet.
With the course of human history, carbon has received a new starring role--providing a harnessable form of energy. Furthermore, some forms of carbon, such as carbon dioxide and methane, are greenhouse gases and intrigue scientists because of their function in climate change. To explore carbon's role in natural and human activities, take a look below at some key topics and questions.