Seven of Earth's Mass Extinction Events
The Precambrian and Vendian Mass Extinctions
Our first mass extinction took place 650 million years ago when all the animals in the world lived in the sea. It claimed 70% of the oceans dominant creatures. A second mass extinction took place at the end of the Vendian and unlike the previous event did not take the hard-bodied animals so much as the soft bodied one, the ancestors of jellyfish, segmented marine worms, and sea pens. These modern animals jellyfish, segmented marine worms, and sea pens exist today because of an evolutionary boom that made all the surviving animals make up for lost time. Scientists believe this extinction may have been caused by the forming of glaciers for the first time in earth’s history since the evolution of life. This was such a large event that almost no microorganisms survived.
The Ordovician Extinction
The Ordovician Extinction happened 434 million years ago and claimed up to 85% of all marine life. There wasn’t any land based life forms yet to decimate. Considered the second most deadly extinction to marine life forms it took with it over 100 families of animals with it. Reef building animals took a hard blow and so did all the animals that lived in those reefs. Brachipods which were one of the most prolific and dominant life forms lost a third of their species. Conodonts, acritarchs, bryozoans, and trilobites suffered similar percentages of losses. This extinction was separated by two events one million years apart from each other.
The first part may have been caused by the earth’s temperature cooling down at a rate they could not evolve to keep up with. The second phase seems to be because the formation of glaciers made the sea levels go down.
The Cambrian and Devonian Mass Extinction
The Cambrian mass extinction was actually a combination of four smaller extinction events that spanned 408-360 million years ago. It claimed most of the species we had come to know and love in the fossil record like trilobites. It is thought to have killed off over 100 families of marine animals and striking a catastrophic blow to archaeocyathids, stromatoporids and early corals, the primary reef builders at the time. These crucial habitat creators did not recover for another hundred million years. All complex life lived in the seas at this time and marine extinction rates climbed to 80% killing off jawless fish and placoderms (armored fish) in the process. Interestingly enough although plant life had found its way to the land as well as amphibians and insects they seem relatively unaffected by this extinction.
Even more interesting is the fact this plant explosion may have been the downfall of its marine relatives. Plants reduce carbon dioxide in the air and with plants suddenly growing on the land in vast quantities the Co2 levels would have plunged pretty dramatically. This could have caused global cooling as well as causing anoxia, a lack of oxygen, in the water by being the first living things to change landscapes. These new plants dug their roots deep into the rocks at the time, breaking it up into sediment that then washed into the water in effect smothering everything under it.
The Devonian Mass extinction may have actually been a collaboration of up to seven separate lesser extinctions spanning 25 million years. If anything it was a slow process.
The Permian Extinction
251 million years ago the earth and seas saw the most complete extinction rate ever losing up to 96% of marine life and 70% of land based animals in a three stage extinction that went from the sea to the land and back to the sea. Sometimes called The Great Dying or “the mother of all extinctions” this is the only extinction to take with it a large number of insects.
A lot was going on in the world when this extinction took place so there’s still some debate about what caused it. Some say that it was the formation of Pangea, the singular and super continent that reduced sea shelves and killed off marine animals. Others think that it was another problem with Co2 and oxygen levels. Besides the formation of Pangea there were also the biggest volcanic eruptions ever to happen on the planet earth. These super eruptions were not caused by volcanoes but enormous vast cracks in the earth as the fault lines moved. Whole sheets of lava could spew from these openings for hundreds of years. This may have made the temperature of the earth rise by as much as ten degrees. This would have turned most temperate habitats into deserts and killed off all but the most adaptable of creatures.
199 million years ago something caused 50% of all marine animals to suddenly die off and up to 80% of all land animals. This era was defined by creatures most people have never heard of that were somewhere between a reptile and a mammal, called conodonts. They all died out as well as most of the giant amphibians and the oceans didn’t fare much better with up to twenty percent of all marine families disappearing.
The late Cretaceous extinction is the one most people know about. It happened 65 million years ago and claimed all the dinosaurs as its most popular victims. They weren’t the only ones to die out as in the sea ammonites, a highly populous species over many millions of years, went with them. This was one of the least deadly extinctions though as only 60-75% of all animals died during this time. On land the dinosaurs died, in the air the pterosaurs flew into the horizon for the last time, and in the sea plesiosaurs memorialized themselves in the fossil record. Although reptiles had among the highest casualties they didn’t come close to the algae, of which up to 90% of all species ceased to be. This is important because little algae are the base to so many ecosystems and food chains that their loss would have been devastating to things far higher up on the food chain.
A meteor impact has been blamed for this mass extinction for many years but how? Basically a space rock six miles across entered the atmosphere and came colliding towards the earth striking what is known today as the Yucatan Peninsula. This killed everything in the area immediately in a rainstorm of fire and ash. It also sent up a great ripple of tsunamis which first crashed ashore and then flooded the coastal regions. The shock would have set off massive volcanic eruptions raising CO2 levels and creating acid rain and the impact would have kicked up a lot of dust that would have made a massive cloud that could have caused a nuclear winter. It’s a nice theory, a bit overdramatic, and it doesn’t sit well with people who believe in Ockham ’s razor (the simplest answer is usually the correct one.) A clue may be in the fact that land-based plant life seems to also have been killed off unlike most other extinctions. Another clue may be in the fact that this extinction appears to have been relatively rapid compared to the others.
Perhaps an even greater mystery is the survival of the animals that lived past the extinction. Large dinosaurs were likely targets in extinction because their massive size means they need massive amounts of food and are fairly inflexible to change. However most dinosaurs were not huge, they were the size of chickens, dogs, and cows. Why did they go extinct while turtles and crocodiles lived on? And why did the tiny mouse-like mammals come to take over the planet with the birds of the time? We’re still trying to figure this one out.
Most people do not realize that scientists are starting to publicly state we are now in the grips of another mass extinction. We are losing the same amount of animals now as were calculated during the extinction of the dinosaurs. The answer to this is pretty obvious – humans. Over hunting, overfishing, the introduction of invasive non-native species, habitat loss, the rise of Co2 emissions, widespread pollution, and global warming make up for many of the contributing factors. Alarmingly we’re seeing the same pattern here as we do in the fossil record. The first species to die out are often the carnivores. Look now at the animals in most critical need of our protection: wild canids, bears, and the large cat species. Once predators disappear old and diseased animals live longer to infect the rest of the herd and overpopulation often leads to rampant starvation as the food sources are depleted. Biologist speculate that as much as one fifth of all life on earth and in the oceans today could be extinct in the next 30 years, and 50% of all species could be dead in the next 100. There is hope though; we as a species can change this. Simple people doing simple things like recycling, reducing their carbon footprint, and by only supporting industries that are self-sustaining can have a huge impact. We can also donate to charities that are working to save certain species and we can cut down on the seafood we buy and eat. We can also support the farming of various meats such as fish instead of capturing them from the wild. Stay informed, make good decisions, and respect the world you live in.