A species is said to be extinct after the last individual of that species dies.
What comes to mind when you hear the word extinction? Bird watchers might offer as an example the passenger pigeon, anglers the blue pike. Children, and many of us adults as well, would surely suggest dinosaurs.
There is an important difference between those suggestions. The pigeon and pike are individual extinctions and there are many other examples: among birds, the great auk, the dodo and the Carolina parakeet; among mammals, the Eastern cougar, West African black rhino and Tasmanian tiger; among reptiles, the golden toad and the Pinta Island tortoise ("Lonesome George" died in 2011).
But the dinosaurs were an entire group of animals: in fact over a thousand species. Those were all wiped out in what has been called a mass extinction or extinction event. Over history extinctions have gone on at a rate averaged over time - the so-called "background rate" - of about six per year. That doesn't seem like many when you consider that we have between 10 and 14 million species today. But life has been here for a very long time and it has been estimated that 99.9% of all the species that have occurred on earth are extinct today.
The dinosaurs were wiped out in a brief period about 66 million years ago in what was formerly termed the Cretaceous-Tertiary extinction event but has now been renamed the Cretaceous-Paleogene event. And it was not just the dinosaurs that were lost: 3/4 of all species went extinct including every land animal weighing more than about two pounds.
Now four additional historic extinction events have been identified. All but one are named for the geologic periods they separate:
Triassic-Jurassic, 201 million years ago. Half of all species were lost. Interestingly this event left an environment in which the dinosaurs became dominant.
Permian-Triassic, also called the Great Dying, 252 million years ago. This was the most severe of all these events: 96% of marine species and 70% of land species went extinct.
Late Devonian, 375-360 million years ago. Three-fourths of all species were lost.
Ordovician-Silurian, 447-443 million years ago. Second worst event: 85% of all species were lost.
What caused those extinction events? Many scientists believe that the Cretaceous-Paleogene event was caused by an asteroid impact in the Gulf of Mexico. Now, however, evidence is accumulating which suggests that all of these events were caused by tremendous amounts of volcanic activity.
On Saturday, March 28, the Buffalo Museum of Science will open a permanent exhibit that will place these five extinction events in perspective.
Karen Wallace, director of Learning and Interpretation for the museum and David Cinquino, the museum's exhibits director, went through plans for this new exhibit with me and I came away very impressed. The exhibit will take the visitor though these five periods, providing examples for each, in doing so drawing upon the museum's extensive collection of fossils and dioramas. It will also show how paleontologists gather evidence as at the museum's Hiscock dig in Byron and give visitors hands-on experiences related to that activity.
But the exhibit will go further: it is rightly titled "Rethink Extinct", because, after providing evidence related to these five events, it introduces us to what may well be a sixth mass extinction taking place today.
Elizabeth Kolbert popularized this idea in her 2014 book, "The Sixth Extinction: An Unnatural History," drawing upon visits with leading biologists, botanists and geologists for evidence about threats to amphibians, bats, coral and rhinos.
Evidence from around the world indicates that recently the background extinction rate has gone up between 1000 and 10,000 times. The Center for Biological Diversity warns: "Unlike past mass extinctions, the current crisis is almost entirely caused by us — humans. In fact, 99 percent of currently threatened species are at risk from human activities, primarily those driving habitat loss, introduction of exotic species, and global warming. Because the rate of change in our biosphere is increasing, and because every speciesŐ extinction potentially leads to the extinction of others bound to that species in a complex ecological web, numbers of extinctions are likely to snowball in the coming decades as ecosystems unravel."
I consider this one of the museum's most important exhibits. I commend the staff for developing it and I urge you to visit.-- Gerry Rising