Mass extinction is when more species are going extinct than are being replaced. Typically this is regarded as a 75% decrease in biodiversity in 2.8 million years.
While 2.8 million years might seem like a long time, 2.8 million is only 0.0006% of the time 4.5 billion years that the Earth has been around. That would only be 52 seconds of your 24-hour day, for reference.
Experts believe that we are living in Earth's sixth mass extinction.
The Other Five Mass Extinctions
There have been five other mass extinctions in the past. We know the cause of a few of them, but some remain a mystery. The theme between most of them was that natural but dramatic events caused them.
1. The Cretaceous Mass extinction - 66 million years ago.
This mass extinction is well known. This was the one that killed all of the dinosaurs, at least all of the non-avian ones. An asteroid hit the Earth in current-day Mexico. The asteroid was estimated to have killed 78% of all species.
2. The Triassic Mass Extinction - 200 million years ago.
The Triassic mass extinction was believed to be caused by "colossal geological activity" and eventually, rising carbon dioxide levels, global climate, and ocean acidification were so intense that 80% of species died.
3. The Permian mass extinction - 250 million years ago.
The Permian was known as The Great Dying - an encouraging name. However, the term is fitting. An estimated 95% of species were killed. There is a debate about the cause of this mass extinction. Scientists believe an asteroid hit the Earth or an enormous volcanic explosion. The volcanic blast is theorized to have increased carbon dioxide, making oceans toxic, and the asteroid theory is believed to have filled the air with so much dust that it blocked the sun, and acid rain began to pour.
4. The Devonian mass extinction - 374 million years ago.
As we go back, scientists struggle to pinpoint the causes of mass extinctions. The Devonian mass extinction is one of those instances. What we do know is that 75% of species were eradicated. It is believed that intense environmental changes occurred - global warming and cooling, reduced oxygen levels, increased carbon dioxide levels, and a rise and fall of sea levels.
5. The Ordovician-Silurian mass extinction - 443 million years ago.
This mass extinction was primarily focused on the seas and oceans. Scientists believe temperatures plummeted, causing massive glaciers to form, draining the oceans significantly. Right after, there was a period of warming which reversed this action causing intense stress on small marine life. 85% of species were killed.
Are we in a sixth mass extinction? How did this happen?
There is a lot of debate about whether we have crossed the 75% biodiversity line, which would put us in the sixth mass extinction. The extinction rate is estimated to be anywhere from 1,000-10,000 times higher than the natural rate due to human involvement.
What is more important to focus on is that if we have not entered the sixth mass extinction, it is looking inevitable.
"Unlike previous extinction events caused by natural phenomena, the sixth mass extinction is driven by human activity, primarily (though not limited to) the unsustainable use of land, water and energy use, and climate change. According to the Living Planet Report, 30% of all land that sustains biodiversity has been converted for food production. Agriculture is also responsible for 80% of global deforestation and accounts for 70% of the planet's freshwater use, devastating the species that inhabit those places by significantly altering their habitats." - World Wildlife Fund
In addition, humans have for years been directly involved in the removal of large animals. Humans unproportionately hunt megafauna as they are perceived as threats to humans and human activities. Stories like the American Bison and The Red Wolf come to mind when thinking of human activity. Both of these used to roam across North America. However, they were both driven to near extinction - an estimated 15 red wolves are left in the wild, and they can only be found in a few counties in North Carolina.
This seemingly "slow burn" of human involvement has been slowly gaining more traction over hundreds of years, and we are truly starting to see the repercussions of our actions. Greenhouse gas emissions are beginning to play a significant role in our climate's change, causing more natural phenomena - once-in-a-lifetime events to occur seemingly annually. Floods, tornados, wildfires, and droughts are becoming an increasingly significant threat to all life on Earth - including humans.
Since all life is directly intertwined, when one species goes extinct, others are due to feel the consequences. Eventually, this pressure escalates to other species, environments, and ecosystems.
Can We Prevent It?
There is a reason that there has been such a significant and intense push towards reversing and changing our human effects on Earth in the last few years.
We have an opportunity to prevent further damage, not necessarily reverse what has occurred.
We must work on utilizing our resources, interacting with wildlife, and spreading the word about global biodiversity issues.
However, as individuals can make an impact, there is an emphasis being placed by scientists to put pressure on policymakers and businesses to change their emissions and global interactions. Individuals are only having a small impact on this mass extinction compared to the small handful of companies causing the vast majority of emissions.
"The future of our world hangs on our making what is perhaps the biggest international effort in history to reduce human impacts. We all have an active role to play, which requires deep transformation of our values, attitudes and behaviours." - Katie Collins, Curator of Benthic molluscs at the Natural History Museum of the United Kingdom.