A Moving Target

Climate change is hardly a new phenomenon.  Even global warming due to greenhouse gases is old hat.  How old?  A group of researchers led by University of Chicago geologist Nicolas Dauphas have been studying some of the oldest rocks on Earth, looking for clues about ancient climate.

They examined rocks from the Canadian Shield -- some of the oldest crust, exposed to view by the action of glaciers during the comparatively recent Ice Ages.  These rocks are about 3.75 billion years old, making them remnants of the first solid crust of the Earth.

What they found was consistent with an atmosphere very rich in carbon dioxide.  Earth in those days had a very high greenhouse effect, which was a Good Thing because the Sun was a lot cooler than it is now -- only 75 percent as bright.  Without a greenhouse atmosphere to trap heat, Earth would have gone through a runaway cooling, leaving it a completely ice-covered world with a few volcanic hot spots.

The story gets interesting after that.  About half a billion years after those Canadian rocks were laid down, living things began to make massive changes to the Earth's environment with waste gases, and nearly made the planet uninhabitable.  Who were the polluters?  Algae. 

Algae and plants using photosynthesis completely transformed the Earth's atmosphere.  The carbon dioxide levels dropped like a rock as they turned it into biomass.  Predictably, the temperature dropped like a rock soon after.  Some scientists are convinced the Earth spent a considerable time completely covered in ice -- the "snowball Earth" model.  Others think conditions may have only been as bad as the more recent Ice Ages.  Either way, it was only the increase in the Sun's energy output which rescued the planet from a chilly fate.

All this is by way of pointing out that climates do change, all the time.  Life and the planet adapt.  It is impossible to prevent the Earth's climate from changing, which means that humans really should be thinking about how we want the climate to change and what trade-offs we're willing to make.