Our home planet is 4.54 billion years old and undisputed proof of life currently dates back 3.5 billion years. Unfortunately, the reality of biological diversification is that many species come while many species go. Looking back over the fossil record, we can see that there’s a steady rate of natural extinction called background extinction in which, by natural selection, species that are unfit to survive die out. However, there’s another type of extinction that’s more abrupt; mass extinction events can be either a single event or a concentrated period of time in which there are a number of extinctions that represent a significant percent of the total population of Earth species at a given time.
Over the course of its life, the Earth has been no stranger to mass extinction events. However, the cosmic finger of blame seems to be pointing directly at us. Historically, there have been five of these mass extinction events incidents to date. The first was the Ordovician extinction, which occurred in two pulses between 447 and 443 million years ago (Ma) and is attributed to lowering sea level and glacial cooling, killing 60 to 70 percent of all species and leaving the early with mostly sea-dwelling life. Next was the Late Devonian extinction of 375 to 360 Ma, killing 50 percent of all genera and affecting most sea-dwelling life. The Permian-Triassic extinction event—also known as the Great Permian Extinction—was the third event and was the most severe, killing up to 96 percent of all species and is thought to have been due to several pulses of extinction brought on by bolide impacts, volcanism, or a runaway greenhouse effect; all species living today are descended from the remaining 4 percent.
The fourth event, the Jurassic-Triassic extinction, occurred 201.3 Ma and killed half or more of all species living at that time although the cause of the extinction has been debated. The fifth and most well-known extinction event, the Cretaceous-Paleogene extinction—also sometimes referred to as the Cretaceous-Tertiary extinction—was an abrupt extinction that occurred 66 Ma after a large asteroid struck in the Gulf of Mexico, killing non-avian dinosaurs and 75 percent of all species living at the time.
Earth’s sixth mass extinction
Per our current understanding, those five events were the most significant mass extinctions in Earth’s history, some taking place over many years while others being somewhat abrupt. However, a new study that has investigated claims that have stated the Earth is currently in the midst of a mass extinction event has found this to be true: The Earth is, in fact, in its sixth major mass extinction and the first since the dinosaurs went extinct. What’s more, human are not only the cause of the mass extinction, but we’re also threatened with extinction ourselves.
Many have made the bold claim that humans have triggered another mass extinction for species around the world, but until now there’s been no way to definitively prove whether or not that’s true. The problem lies in proving whether or not the current rates of extinction are significantly higher than natural rates of extinction, called background extinction, which is itself a difficult thing to estimate.
If a conservative estimate of today’s rate of extinction is significantly higher than an over-estimated rate of background extinction, there’s a very strong possibility that Earth is experiencing its sixth mass extinction event.
For one thing, many extinction estimates tend to over-estimate to sort of emphasize the results as if they’re being underlined, but this is also thought to have exaggerated the current mass extinction crisis. Therefore, the authors of this study wanted to used as conservative numbers as possible, essentially the bare minimum extinction rate that we could possibly be experiencing. Meanwhile, the standard rate of background extinction will be estimated on the higher end. The idea is if a conservative estimate of today’s rate of extinction is still significantly higher than an over-estimated rate of background extinction, there’s a very strong possibility that the Earth is experiencing its sixth mass extinction event.
Paul Ehrlich, the Bing Professor of Population Studies in biology and senior fellow at the Stanford Woods Institute for the Environment, and his team of scientists began by finding an estimate for natural background extinction. The group analyzed fossil records directly as well as numerous reports of extinction counts, choosing a rate estimate that’s twice as high as those of the studies they’d used. Comparing that figure to the conservative rates of current extinction, Ehrlich and his group found that the current rate of extinction is 100 times faster than the normal, natural rate of extinction.
“We emphasize that our calculations very likely underestimate the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity’s impact on biodiversity,” the researchers write.
Over the course of our tenure on the planet, the human population has reached astronomical proportions while we’ve wrought increasing levels of destruction on both the micro and macro levels. The many negative effects we’ve had on the environment include land clearing for farming, logging, and development; introduction of invasive species in non-native locations; increasing carbon emissions that have caused significant climate change and the acidification of the world’s oceans; introduction of toxins that have altered and even poisoned entire ecosystems; and so on.
Earth’s biodiversity threatened by our effect on rate of extinction
Due to the effect we continue to have on the planet, there are startling numbers of species that are currently facing extinction. According to the International Union for Conservation of Nature, which maintains an authoritative and comprehensive database of all threatened and extinct species, more than 41 percent of the world’s amphibian species and 26 percent of the world’s mammals are currently on the brink of extinction. “There are examples of species all over the world that are essentially the walking dead,” Ehrlich said.
Some might morbidly wonder why it’s such a big deal to kill off a few species out of the millions that continue to survive, but at the current rate of extinction we will eliminate much of the world’s biodiversity and the benefits that such biodiversity affords within three generations. What’s more, the result of the extinction of species is that whole ecosystems are affected and often threatened with extinction themselves. We also run the risk of losing many important ecosystem services—such as honeybees’ crop pollination and the wetlands’ natural water purification.
According to the researchers, the effect we are having can be summed up with the analogy of the human race sitting in the tree of life. “We are sawing off the limb that we are sitting on,” Ehrlich says.
What do you think about our effect on the environment? Is calling this a mass extinction event an overstatement or an accurate description of the damage we’re causing to the planet? Comment below.
Read more about this study on Science Daily and check out the original study published at Science Advances. If you want to learn more about mass extinction events, check out an overview of the five mass extinction events from National Geographic.