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Kevin Walsh via Flickr // CC BY 2.0
Kevin Walsh via Flickr // CC BY 2.0

5 Extinctions That Wiped Much of Life off Planet Earth

Kevin Walsh via Flickr // CC BY 2.0
Kevin Walsh via Flickr // CC BY 2.0

by Aliya Whiteley

The more we get to know about the history of the Earth, the more incredible it becomes. Our planet formed about 4.5 billion years ago, and for the first billion years it was without life. Then organic molecules began to form simple cells.

It’s tempting to think that from those first cells the business of evolution took hold and created the plants and animals we see today, but this simplified version overlooks some of the most catastrophic developments that happened along the way. Five mass extinction events have wiped out nearly every living thing on this planet. So the next time you’re feeling less than brave, remind yourself that you are descended from some seriously tough survivors. You’re already one of nature’s great success stories.

1. ORDOVICIAN-SILURIAN EXTINCTION—445 MILLION YEARS AGO

Most life forms were still living in the oceans at the time of the first mass extinction. There are many theories as to how that happened: global cooling that brought on an ice age, volcanic gases, or maybe changes in ocean chemistry. Whatever the cause, about 85 percent of species were wiped out.

2. LATE DEVONIAN EXTINCTION—375 MILLION YEARS AGO

The oceans recovered and teemed with life once more, and that diversity had begun to spread onto land at the time of the second mass extinction, when 79–87 percent of all species died due to environmental change. A series of several extinction events spread over approximately 40 million years wiped out most of the life on earth. The cause is unclear, but some scientists have theorized that the sudden increase in plant life could have triggered a period of anoxia (lack of oxygen). Other suggestions include volcanic eruptions on a huge scale, or another ice age.

Although plants may have triggered the destruction, it was the marine life that was hardest hit. Armored fish died out completely. Reef ecosystems vanished from the seas and were not seen again for the next 100 million years. But there were some who benefited: Into these gaps in the oceans’ ecosystems came some of nature’s hardiest survivors—the sharks.

3. PERMIAN-TRIASSIC EXTINCTION—250 MILLION YEARS AGO

This is also known as the Great Dying, and with good reason: 70 percent of land species and 90 percent of marine species disappeared, including half of all marine families. Plant life also suffered; only a few forests remained. It’s the only event in which insects also died out en masse. The devastation to life was so thorough, this mass extinction event is known as the Great Dying.

The culprit was, once again, environmental change. An enormous volcanic event in an already hot, dry climate led to a massive increase in carbon dioxide, and as ice sheets melted, methane escaped into the atmosphere, adding to the problem. These greenhouse gases led to the creation of anoxic conditions in marine habitats once more.

4. END-TRIASSIC EXTINCTION—200 MILLION YEARS AGO

After the Great Dying, it took approximately 20 million years for the Earth to recover. Unfortunately, soon after the Earth returned to its previous level of diversity, the next mass extinction came along and nearly wiped out the dinosaurs just as they were getting started. But it was the mammal groups who really suffered this time around, along with large amphibians: 76 to 84 percent of all species died out. The culprit may have once again been volcanic activity.

But dinosaurs managed to recover remarkably well, becoming the dominant creatures on the planet after this particular extinction event. And so they might well have remained, if it wasn’t for what happened next …

5. END-CRETACEOUS MASS EXTINCTION—66 MILLION YEARS AGO

This is the event we all know about. Many experts theorize that a large asteroid hit the Earth and contributed to rapid environmental changes. Sea levels plummeted, volcanic activity threw ash and poisonous gases into the air, and 71 to 81 percent of all species died. All non-avian dinosaurs perished, leaving the way clear for the small mammals that managed to survive.

BONUS: HOLOCENE EXTINCTION—10,000 BCE to ONGOING

And here we are today, having evolved from those small mammals. Are we in the grip of the sixth mass extinction of life on our planet? It's unclear how many species we're losing annually—one widely cited estimate is 140,000 species per year [PDF]—but it’s difficult to be sure of the size of the problem, as less than 3 percent of species on the planet are thought to have been formally assessed for risk.

The growth of humanity may be causing a loss of biodiversity, but the good news is that we have developed to the point where we might be able to do something about our own impact on the planet. We’re already aware of the problem—and there might even still be time to fix it.

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AFP, Stringer, Getty Images
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Stones, Bones, and Wrecks
The Most Complete Fossil of an Early Human Relative Goes on Display
AFP, Stringer, Getty Images
AFP, Stringer, Getty Images

Twenty years after it was discovered in an African cave, one of the most important fossils in the quest to demystify human evolution is finally on display. As Smithsonian reports, Little Foot, an Australopithecus specimen dating back more than 3 million years, was revealed to the public this month at the Hominin Vault at the University of the Witwatersrand’s Evolutionary Studies Institute in Johannesburg, South Africa.

Paleontologist Ron Clarke discovered the first bone fragments from the fossil in 1994. The pieces came from the remains of a young female’s feet, hence the nickname. Clarke and his team spent years excavating Little Foot bit by bit from the Sterkfontein cave system in South Africa until the bones were fully removed in 2012. The shattered remains had been embedded in a concrete-like material called breccia, making them incredibly tricky to recover. But the sum of the parts is monumental: Little Foot is the most complete Austrolopithecus fossil known to science.

The hominid genus Austrolopithecus played an essential early role in the chain of human evolution. Lucy, another famous hominid fossil, is a member of the same genus, but while Lucy is only 40 percent complete, Little Foot retains 90 percent of her skeleton, including her head. It’s also possible that Little Foot surpasses Lucy in age. Most paleontologists agree that Lucy lived about 3.2 million years ago, while one analysis places Little Foot’s age at 3.67 million years.

Austrolopithecus is believed to have spawned Homo, the genus that would eventually contain our species. The discovery of Lucy and other fossils have led scientists to designate East Africa as the cradle of human evolution, but if Little Foot is really as old as tests suggest, then South Africa may deserve a more prominent point in the timeline.

Following Little Foot’s public debut, the team that’s been studying her plans to release a number of papers exploring the many questions her discovery raises.

[h/t Smithsonian]

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NM Museum of Natural History & Science
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science
Scientists Find a 245-Million-Year-Old Horseshoe Crab Fossil That Resembles Darth Vader
NM Museum of Natural History & Science
NM Museum of Natural History & Science

Horseshoe crabs have scuttled through Earth’s shallow ocean waters for hundreds of millions of years, but scientists recently discovered the fossil of one that looks like it’s from a galaxy far, far away. As Newsweek reports, the 245-million-year-old creature’s shell is shaped like Darth Vader’s helmet, which prompted researchers to name the prehistoric critter Vaderlimulus tricki. (Tricki pays homage to Trick Runions, the man who found the fossil.)

Paleontologists from the New Mexico Museum of Natural History and Science and the University of Colorado described the Vader horseshoe crab in a new report published in the German journal Neues Jahrbuch für Geologie und Paläontologie. Discovered in Idaho, Vaderlimulus tricki lived during the late Triassic era and belonged to a now-extinct family called Austrolimulidae. During its lifetime, it inhabited the western coast of the supercontinent Pangea.

Vaderlimulus tricki's unique shell can be chalked up to evolution, scientists explain in a news release, as the creatures were “expanding their ecological range from marine into freshwater settings during the Triassic and often exhibit body modifications that provide them with a bizarre appearance by modern standards."

Horseshoe crabs have survived at least 470 million years on Earth, and are often referred to as “living fossils.” But individual species died out over the millennia (only four are currently alive today), and fossils of horseshoe crabs are few and far between. When new ones are discovered, they often belong to a species that was previously unknown to science. Vaderlimulus tricki, in particular, is the first horseshoe crab from the Triassic period to have been found in North America.

[h/t Newsweek]

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