It was when he began to collaborate with the American microbiologist Lynn Margulis that the full theory began to take shape. Margulis was studying the processes by which living organisms produce and remove gases from the atmosphere. In particular she was examining the role of microbes which live in the Earth's soil. Working together, they managed to uncover a number of feedback loops which could act as regulatory influences. An example is the carbon dioxide cycle.
Volcanoes constantly produce massive quantities of carbon dioxide.
Since carbon dioxide is a greenhouse gas, it tends to warm the planet. If left unchecked, it would make the Earth too warm to support life. While plants and animals take in and expel carbon dioxide through life processes such as photosynthesis, respiration and decay, these processes remain in balance and don't affect the net amount of the gas. Therefore there must be another mechanism. One process by which carbon dioxide is removed from the atmosphere is rock weathering, where rainwater and carbon dioxide combine with rocks to form carbonates.