Remember the mass-extinction event that wiped out the dinosaurs? Earth is apparently on the verge of another great biological extinction, and humans are solely to blame.
Scientists have previously classified five large-scale losses of animal life as mass-extinction events, all of which occurred millions of years ago. In recent years, the planet has seen the loss of hundreds of species of animals, and according to a new analysis from an international team, the planet may be in the early days of its sixth mass-extinction event.
As part of the study, researchers analyzed previous studies and scientific data to draw their conclusion that human activities and population surges worldwide -- not a catastrophic event, like an asteroid impact, for example -- are responsible for the drastic decline of animal life. Lead author Rodolfo Dirzo, a biology professor at Stanford University, cites actions like overexploitation of resources and habitat destruction as examples of harmful human activities.
Since 1500, 322 terrestrial vertebrates have become extinct, the authors said in their analysis, published Friday in the journal Science. Of the remaining land-dwelling species of vertebrates, there has been a 25 percent average decline in abundance. The situation also appears to be dire for invertebrates, with a 45 percent decline in monitored species.
So what does this mean for the planet?
There may be unforeseen consequences, aside from the possible extinction of threatened species.
"We tend to think about extinction as loss of a species from the face of Earth, and that's very important, but there's a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well," Dirzo said in a statement.
Dirzo pointed to potential trickle-down effects, such as threats to ecosystems that are currently stable and even risks to human health.
"Where human density is high, you get high rates of [animal decline], high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission," Dirzo said in the statement, adding, "It can be a vicious circle."
Biologists from Duke University reported in May that Earth is on the verge of the sixth mass-extinction event. Their study, which focused on the past and present rates of extinction, found that plant and animal life are going extinct 1,000 times faster than they did before the arrival of human populations.
While humans may be responsible for kickstarting another mass-extinction event, there might still be time to react. As Scientific American notes, current extinction rates suggest that humans still have a century or two to change course.
Ben Collen, a lecturer at the University College of London and a co-author of the new mass-extinction analysis, says scientists need to focus on species that are thriving.
"Prevention of further declines will require us to better understand what species are winning and losing in the fight for survival and from studying the winners, apply what we learn to improve conservation projects," Collen said in a statement. "We also need to develop predictive tools for modelling the impact of changes to the ecosystem so we can prioritize conservation efforts, working with governments globally to create supportive policy to reverse the worrying trends we are seeing."