Sometimes you can live through an avalanche.

Rob Rice, a fellow reporter at the Deseret News, was cross country skiing recently when "suddenly, with nothing that would give you any sort of indication, everything started moving.""The whole mountainside started moving, and it swept me up and carried me down the mountain with this incredible mass of snow." He fell down, but the avalanche turned out not to be deep enough to bury him.

G. Jon Roush, a Ph.D. rancher and consultant from Montana, the former president of the board of the Nature Conservancy, says we are about to be swept along by another kind of avalanche.

"We are on the verge of a species extinction avalanche," he said during a speech for Project 2000, a non-profit group that is attempting to serve as a catalyst for informed, reasoned planning in Utah.

"Momentum will definitely be on the side of annihilation."

According to Roush, it's reasonable to conclude that, except for nuclear war, extinction of other species is the most serious danger the human race has ever faced. It's happening at a terrible pace.

Within the past two centuries, 85 percent of the forest birds in Hawaii became extinct or nearly extinct. Their demise is blamed on rats, mongooses and disease-carrying mosquitoes introduced after Captain Cook's discovery of the islands.

In the West, the alien species that are most destructive to native plants and animals are probably herds of cattle and sheep, he said.

Hawaiian birds and Utah's desert tortoise are in trouble because of competition with introduced animals. Worldwide, a worse scourge is habitat destruction.

As man continues to plant, dam and bulldoze, species are pushed out of the ecological niches where they thrived - and they die.

In Brazil, enough of the rain forest to cover Austria is chopped or burned every year.

Extinction is normal, as he pointed out. During the height of the last major ice age, 15,000 years ago, North America lost an estimated three species per century. But now the world is losing a species per day.

By early next century, ecologists predict we'll be losing hundreds of species daily, he said. "Our grandchildren will probably live in a world with half the number of species that populate ours."

The loss is incalculable, just in terms valuable medicines from worms and frogs that have evolved complex chemistry over the millennia. And life in a drab world with only a few species would be dreary indeed.

But it's worse than that. It's a threat to our survival.

The conjunction of life, long celebrated by poets, is not a flight of fancy. It's reality and we ignore it at our peril.

Chains of cause and effect can be subtle and intricate, Roush warned. Whenever a species dies out, that can jeopardize others.

Illustrating this linkage of life forms - like mountain climbers roped together - he cited the wasps that service figs. Each fig species has its own species of wasp; the wasps evolved with the figs and they depend on each other. Wasps lay their eggs in figs, which support the wasps' young. In return, the wasps are essential in fertilizing figs as they fly from vine to vine.

The superstructure of jungle life depends on the figs - first the fruit-eating insects and animals, then the predators that feed on them. If the wasps are killed off, say by pesticides, the whole structure crashes.

Roush said, "Life on Earth is a chancy enterprise and we had better not forget that." That's so in the best of times.

Times are getting much worse, with these man-made extinctions.

"Our own survival utterly depends on the survival of other species," he said.

"Every day we're losing these species. Every day we're losing a universe of possible values . . . The whole living fabric of our planet is becoming tattered."

Sometimes you can't live through an avalanche and one is starting. We see cracks in the snow and hear an ominous creaking . . .

People had better wake up to the danger.