Terra Firma: Not as 'Firma' as You Might Think
By Our Green Team | Mar 5 2010, 15:17

Terra firma. Rock solid. On solid ground. While expressions like these suggest the Earth as a fixed and immutable place, reality says otherwise.

Over its 4.5-billion-year history, our planet has changed dramatically, sometimes at a slower-than-snail's pace, sometimes in sudden and cataclysmic fashion. The massive asteroid that slammed into the Earth 65 million years ago, for example, set off widespread fires, magnitude 10-plus earthquakes, devastating landslides and tsunamis, and a deadly global winter that killed off the dinosaurs and some 50 percent of all plant and animal families.

Today, astronomers track the heavens for signs of similar sized asteroids that might be headed our way. But giant hunks of rock in space aren't the only potential upheaval our planet might face.

Consider the magnitude 8.8 earthquake that struck Chile in late February. The massive quake not only toppled buildings and set off tsunamis (the most deadly occurring along the Chilean coast) but actually shifted the Earth's axis of rotation and shortened the length of a day by 1.26 millionths of a second .

Climate change could also affect how our planet spins by shifting the distribution of mass as ice caps melt. In fact, scientists say a warmer globe is also likely to be a more geologically active one as stresses on the surface change. At a conference in London last fall, researchers discussed a host of impacts that global warming could bring on, including earthquakes, landslides and tsunamis .

Then there's the Earth's old habit of reversing magnetic poles every so often. It appears we're long overdue for a switch , since the last one took place about 780,000 years ago and they were coming every 20,000 to 50,000 years or so apart before then. The possible effects such a geomagnetic flip might have on society is uncertain .

Society, on the other hand, is bringing about some planetary changes of its own. Even if you discount climate change, the human impact on Earth is already significant in many ways... and growing. Last year, an international team of researchers warned that we've already overstepped the planet's ability to cope in terms of climate, biodiversity loss and the nitrogen cycle, and are pushing the limits on ocean acidification, freshwater use, land system changes and stratospheric ozone depletion. Any one of these impacts could have huge ramifications for life on Earth - taken together, they're beyond worrisome.

In fact, a growing number of scientists today believe that humans have impacted the planet to such a degree that we've brought about a whole new geologic epoch: the Anthropocene .

It's all a far cry from life as we knew it in the 1970s, when fooling Mother Nature and inviting her wrath meant replacing butter with margarine , isn't it?