Plains CO2 Reduction (PCOR) Partnership

Carbon and CO2 on Earth – Things Have Changed!

Carbon (C) is a naturally occurring element on Earth and in other places in the universe. Even though only a very small portion of the Earth is carbon, the Earth still contains about 121,000,000 GtC of carbon (121 million gigatons of carbon or 121 million billion metric tons of carbon).

The amount of carbon on the Earth today is the same as when the Earth was formed about 4.5 billion years ago. But the distribution of the carbon has changed over time. In other words, we have the same number of atoms of the element carbon—they are just in another place or might be combined in a different way. Over time, this change in the form and location of materials that contain carbon has affected the greenhouse gas mix in the atmosphere. Because the atmosphere is like a blanket around the Earth, changes in the gas mix in the atmosphere has affected the amount of heat energy in the atmosphere. These changes have affected climate through time. Learn more.

Scientists tell us that the Earth started out about 4.5 billion years ago as a ball of hot gases. About 3.5 billion years ago, the Earth was cool enough to have a solid crust as well as a primitive atmosphere. At the same time, CO2 was being formed deep in the earth by geologic processes, and this CO2 was being released to the atmosphere through volcanic eruptions.

Coral Garden, Great Barrier Reef, Cairns, Queensland, Australia.

According to scientists, the atmosphere of half a billion years ago contained about 15 times the CO2 it contains now. This was just at the time that plants and animals were becoming plentiful. Plants lived by taking carbon dioxide out of the air and using the carbon to make stalks and sap. Animals were appearing that could make shells and skeletons using carbon. In the oceans, for example, billions of tiny coral animals combined the carbon dissolved in the ocean with dissolved calcium (Ca) and oxygen (O) to make their tiny skeletons. Over time, accumulations of these tiny skeletons made thick carbon-rich deposits we call coral reefs. Many of these reefs have been preserved by burial in the geologic record; we know them as limestone. A lot of the carbon that was once in the atmosphere is trapped in the limestone rock that is now buried deep underground!

Plants obtain carbon directly from the atmosphere by converting CO2 to C and O2 through photosynthesis. Beginning about half a billion years ago, plants became plentiful in the oceans. Later, the plants became plentiful on the land. Geologists call the time period of 400 million years ago “carbon-iferous” (“full of carbon”) because so much carbon was taken from the air by plants and sequestered when the plants were buried and eventually preserved in deposits of carbon-rich coal.

Carbon-Rich Coal.

Carbon is also a major chemical building block in animals. Animals are most plentiful in the ocean. If conditions are right (for example, a very low level of dissolved oxygen in the water), the bodies of marine animals can be preserved as oil. Major oil deposits of oil are all over the earth. Major periods of oil creation occurred 400 million years ago and 60 million years ago.

Over the last 300 million years, scientists tell us that the level of CO2 in the atmosphere have varied from 5 times the current level to levels similar to those we have in modern times. Learn more.

When humans burn fossil fuels, heat limestone to make lime for cement, or plow new areas for farming, carbon is released to the atmosphere that would otherwise have remained in long-term storage. These practices have made humans players in the carbon redistribution game. Learn more. Now, scientists are looking at the natural processes that lead to carbon storage and are developing sequestration strategies as part of the larger effort to address concerns over climate change.1 Learn more.

  1. Pacala, S., and Socolow, R., 2004, Stabilization wedges—solving the climate problem for the next 50 years with current technologies: Science, v. 305, p. 968–972.