Grow-up time?

Most scientists have long taken for granted that there had to be a multitude of alien civilizations out in our vast galaxy. Among so many stars, how could there not be? But of late, many scientists are starting to wonder: Is the Earth it?

Consider: The Earth is in the right 5 percent or so of the galaxy. Too far out, there's insufficient heavy elements, like the radioactive material that keeps continental plates moving and alive with energy. Too far in, it's a madhouse of dangerously close stars, a constant bombardment of comets and rocks, and fierce radiation. Also, our sun is just the right size. Stars that are too big don't last long enough to nurture life, stars that are too small (which are most of them) emit lower energy and create a habitable zone that's too close, resulting planets tidally locked so only one side always faces the sun. In addition, the earth is lucky in its neighbors. For instance, Jupiter is just in the right place and just the right size to steer most meteors and comets away. Meanwhile, our Moon is just the right size and in the right position to act as a gyroscope, minimizing changes in the tilt of the Earth's axis.

Add all the wondrously complex details that keep the planet alive - the rock cycle, the water cycle, the carbon cycle, and so on. The Earth, created with precisely the elements it needed, might exist despite overwhelming odds against it. Our planet might be a very special place indeed.

Do we treat it that way? Afraid not. Each year we lose about 70 gigatons of precious topsoil to the sea. We've filled in important wetlands. In the U.S. we've paved an area greater than the state of Ohio.

This is not to mention the huge and increasing changes we've made to the atmosphere, and all the extinctions we've caused in the biosphere. Geological eras are based on mass extinctions. All by ourselves, we've erased enough species to put paid to the current Cenozoic era - a 65-million-year era of time is crashing to an end.

Professor Michael E. Wysession of Washington University in Lt. Louis reminds us that humans are new to all this, and we're bound to make mistakes. He likens us to children.

Children grow up. Will we?