Even 100,000 years ago, explorers might have found only the fossils of plant and animal species, large and small, that shared the continent when it was separated from South America by open sea. The continents were linked by an upheaval that produced the Isthmus of Panama. The species that did survive, I believe, were not always the fittest of the era in which they lived but those of lineages that proved to be the most adaptive to change. From all I have read, the planet was a turbulent place when humans were emerging from Africa to begin to populate every continent on Earth. The last 8,000 years have been rather stable, but we must accept that the lessons of history show it cannot last.
Ecological disasters come and go, and the planets, man and other creatures and plants have survived.
Today's land developers forget they are part of nature, that they too evolved from creatures that walked the Earth for millions of years. But environmentalists are fooling themselves when they paint those lovely pictures of a return to nature where the birds sing in the trees and men and women weave baskets and make love when the sun goes down. People evolved from chimpanzees through intermediate creatures until they emerged only 100,000 years ago as modern humans with big brains. In the beginning, before they put their big brains and tools to work, they huddled in caves and occasionally were dinner for predators. Man's degradation of the environment began not with the industrial revolution or burning of tropical forests.