The Sixth Mass Extinction

by Ray Grigg

One of the most sobering discoveries made by such scholarly disciplines as biology, anthropology and paleontology is the extent of species extinction we are causing by our impact on Earth’s diverse ecologies. This extinction event, so evident to science that it is being identified as a geological epoch aptly called the Anthropocene, is barely noticed by the brief experience that accrues during the short decades of our individual lives.

But scientists note that the present extinction of species is so massive and abrupt they have identified it as the sixth of its kind in the 3.5 billion years of life on Earth. Estimates are — depending on our behaviour between now and the end of the century — that plant and animal biodiversity could be reduced by a third. And this extinction rate could continue after 2100, the result of our reputation for environmental neglect and procrastination, coupled with the ecological impact of supplying resources to an expected population of 11 billion people. From the perspective of Earth’s long history, the current impact on our planet’s biota is essentially instantaneous.

As a comparative measure of this impact, the following are the five previous mass extinction events, identified by name, millions of years ago (Ma), and percent (%) of species extinction:

  1. Ordovician, 450 – 440 Ma, 60 – 70%;
  2. Late Devonian, 375 – 360 Ma, 70%;
  3. Permian or “Great Dying”, 252 Ma, 90 – 96%;
  4. Triassic, 201 Ma, 70 – 75%;
  5. Cretaceous, 66 Ma, 75%.

The Cretaceous is the “biotic crisis” most known to us. Evidence suggests it was caused by a huge meteor strike, a collision that obliterated almost all non-avian dinosaurs, thus making way for the birds and mammals that now dominate Earth’s animal species. This new assortment of vertebrates includes us, recently identified as the cause of the current sixth mass extinction.

A quick survey offers an explanation. We have converted close to 40% of the land mass of the planet to our purposes, while impinging on much of the rest with our resource extraction, roads, railways and recreation. Indeed, we proudly intrude on nearly every conceivable niche of the biosphere, then inundate pristine and newly discovered places with hoards of adventurers and tourists who are eager for novel experiences. In the process, we have displaced innumerable species, emitted into the atmosphere close to 2 trillion tonnes of carbon dioxide, and released into nature gargantuan quantities of inorganic, chemical, plastic, medicinal and toxic wastes.

The dodo, great auk and passenger pigeon are the conspicuous surface of the extinctions we are causing. Most tiger species no longer exist. Populations of rhinos, hippos, primates, lions and leopards are collapsing. So, too, are bird, turtle, amphibian, shark and fish populations. Extirpation of mammals is common. Plant varieties are being decimated by habitat alteration, alien species and climate change. Industrial fishing and ocean acidification are dramatically compromising marine ecologies. Scientific estimates place the current extinction rate at 1,000 times higher than the normal background rate of about one species per million per year.

Of the approximately 5 billion species that have ever lived on Earth, 99% are now extinct. While this historical information gives some perspective to our present behaviour, it provides us with few excuses.