Our planet is an ever-changing sphere of wonder and mystery. By studying sediments, ice-core samples, trees, and fossils, scientists have been able to piece together some of its phenomenal history and evolution. Humans have been here for a relatively short time, our survival and prosperity made possible by the unique conditions that unfolded to create the current balance.

Throughout human history, we have been subject to forces of nature, but overall, the Earth has been in a period that has allowed us to flourish. We can't take that for granted. When we look through a scientific lens, we see amazing hydrologic and carbon cycles, processes such as photosynthesis that allow us to breathe and eat, and so much more. We also see droughts, floods, insect infestations, and mass extinctions that can radically alter the balance of life.

A massive release of carbon into the atmosphere can trigger cataclysmic events. It's something we're facing now, as we burn fossil fuels as fast as we can dig and suck them out of the ground to keep our homes and cities warm and lighted, and to propel ourselves in machines weighing more than 10 times as much as the often-solo person they are transporting.

This is not the first time the Earth has changed in response to carbon overload. Scientists have found that the planet experienced rapid warming about 56 million years ago, long before humans arrived. According to an article in the October issue of National Geographic, a "massive and geologically sudden release of carbon" during the Paleocene-Eocene Thermal Maximum, or PETM, altered the planet's systems, making it possible for new life forms to appear and thrive, including, eventually, humans.

Evidence suggests that the carbon released then was equivalent to the amount that would enter the atmosphere if we burned all the Earth's reserves of coal, oil, and natural gas. The warming effects are believed to have lasted 150,000 years until the carbon was reabsorbed.

The main difference between now and then is that we are fuelling the current change, whereas 56 million years ago, it was a natural phenomenon -- although scientists are still not entirely sure what caused it. The Earth was experiencing massive tectonic upheavals at the time, which would have sparked volcanic activity, but that only accounts for a relatively minor release of carbon and subsequent small increase in global temperatures, even if a comet impact were added to the mix.

The most likely scenario is that the slight warming from those events, or from fluctuations in the Earth's orbit, caused methane hydrates to melt, releasing massive amounts of methane into the atmosphere. As the National Geographic article points out: "The hypothesis is alarming. Methane in the atmosphere warms the Earth over 20 times more per molecule than carbon dioxide does, then after a decade or two, it oxidizes to CO2 and keeps on warming for a long time."

Methane hydrates are ice-like water molecules that form around a molecule of methane. In cold temperatures and under high pressure, they remain stable. Large deposits lie under the Arctic and the seafloor. Scientists believe the current warming could be enough to release these extremely potent greenhouse gases.

Swedish geologist Birger Schmitz, who has studied the PETM science, told National Geographic that we can either wait to see what the result of such a large release will be, or we can look at what happened 56 million years ago. And what happened then "was a wholesale rearrangement of life."

Why would we undertake such a drastic experiment that threatens the survival of the human species when we have pretty good evidence of what the outcome will be? The main reason is that many of us are not willing to give up our newly acquired luxuries and economic systems regardless of the effects on ourselves, our children, our grandchildren, and all other life on the planet. We don't seem to be willing to slow down the pace of fossil fuel extraction and use while we shift to cleaner energy sources and more rational ways of living within this finite biosphere.

We have some tough choices to make. Science increasingly tells us that we must choose wisely and quickly.

Dr. David Suzuki is a scientist, broadcaster, author, and co-founder of the David Suzuki Foundation. Written with contributions from David Suzuki Foundation editorial and communications specialist Ian Hanington.

Learn more at www.davidsuzuki.org.