Mother Earth - Gaia - poses the same challenge. "The Gaia hypothesis," Wikipedia tells me, "is an ecological hypothesis that proposes that living and nonliving parts of the earth are a complex interacting system that can be thought of as a single organism." If so, then this organism has undergone a species shift in the first decade of the 21st century.

Three fundamental changes mark it. The first is climate change. The evidence is now overwhelming. Those who continue to deny or question the phenomenon are whistling in the dark.

The second is resource scarcity. National Geographic heralded the change last year when its cover story told us to "Say goodbye to cheap oil." Recent record highs may back down, but we will never see cheap petroleum again. Reserves are identified, finite and declining. Demand is rising quickly as China, India and others emerge as red-hot economies, while our thirst remains insatiable.

Other fundamental resources are also at risk of scarcity. The cost of rice is soaring. Corn prices are also climbing due in part to the demand for ethanol as a petroleum replacement. Water, too, is a precious commodity in many parts of the world. As populations continue to grow, and as we blithely develop arid areas like the American Southwest, the pressure on water supplies will intensify. The more farmland we pave over for housing developments and shopping malls, the less remains to meet the world's growing appetite.

The third is violence. The century was barely 8 months old when the World Trade Center towers imploded. Since Sept. 11, 2001, we've been at war. Regardless of what any presidential candidate tells us, no end is in sight.

Meanwhile, on the home front, the Virginia Tech massacre is emblematic of the new violence that has entered our culture like a virus. When a police officer was shot to death last weekend in Philadelphia, comrades wondered out loud how young men, armed to the teeth, could fire on a police officer, seemingly oblivious of the consequences to themselves.

Try factoring into your analysis the 49 percent high-school- graduation rate in the Philadelphia School District, and you begin to see why these desperados act with wanton abandon.

The Virginia Tech event indicates that alienated college students are capable of even more irrational acts. The Philly cop was killed by habitual crooks with few obvious alternatives. The Tech gunman was an angry nut who finally cracked, but he was living the American dream denied to inner-city dropouts.

THE WEATHER has always been unpredictable. Resources have always been scarce. Violence is a hallmark of the human condition. So what's so special about now?

Well, magnitude is one thing: The largest human population in world history and still growing, plus the unprecedented resource demands and sense of desperation that go along with it.

But I'm arguing for recognition of qualitative change. For the first time, humans apparently have caused global climate change. For the first time, we face the possibility of worldwide exhaustion of critical resources.

And for perhaps the first time, we face forms of lethal human behavior on a grand scale that can be attributed only tangentially, at best, to traditional human aspirations and needs.

I mean, what did the Virginia Tech murderer want? Or a suicide bomber? Or a cop-killer? When certain death for each of them is in the equation, traditional political and social solutions to crime and civil unrest are beggared.

This is why I say that planet Earth has had a species shift in this first decade of the new century. Gaia is qualitatively a different beast than it was in the late, great 20th century, which (for Americans, at least) will be remembered some day soon as a golden age. *

Jim Castagnera is the associate provost and associate counsel at Rider University in New Jersey.