Agassiz was a staunch creationist; he taught that after every global extinction of life God created every species anew.
Every ancient extinction happened at a time when Earth was also seeing disruption in the carbon cycle the natural process that links cellular respiration (which releases carbon dioxide, or CO2) and photosynthesis (plants take up that CO2 to grow).
Although every mass extinction has been marked by a disruption of the carbon cycle, there's also evidence that, at other periods in our planet's history, the carbon cycle was disrupted and most living things didn't go on to die.
Of course, not every de-extinction project faces the same ethical or even technical hurdles and mammoths are not the only candidate species for de-extinction whose resurrection might have ecological benefits.
Environmental changes — like warming seas, ocean acidification, and pollution — bring tens of thousands of species to the brink of extinction every year.
For example, given a sample of 10,000 living described species (roughly the number of modern bird species), one should see one extinction every 100 years.
"We're pushing species to extinction every day, and it's an overwhelming job, frankly, that the Fish and Wildlife Service has," Mr. Parenteau said.
"We now need a prompt, comprehensive and well-enforced recovery plan to get the koala back off the threatened species list, and we need protection for other species not as famous as the koala but still sliding closer to extinction every day".
What's more, the world is currently so overpopulated that we're driving over 50 species of plants and animals to extinction every day, destroying rain forests many times faster than they can regenerate and in some areas consuming fresh water at least 10 times faster than it is being replenished.
The Stern Review, the U.K. government's premier report on the economics of climate change, estimated a 0.1percentt risk of human extinction every year.
