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.

nextArticle.image_alt|e
Courtesy of October Films
This Scientist's Idea of the 'Perfect' Human Body Is Kind of Terrifying
Courtesy of October Films
Courtesy of October Films

The perfect human body has the legs of an ostrich, the heart of a dog, and the eyes of an octopus, according to anatomist Alice Roberts. And it’s utterly terrifying.

With the help of anatomical artist Scott Eaton and special effects designer Sangeet Prabhaker, Roberts created a life-size replica of herself that fixes many design flaws inherent to the human body, Motherboard reports. Roberts unveiled the sculpture on April 23 at the Science Museum in London. On June 13, the BBC released a documentary about the project.

Among the flaws Roberts’s sculpture corrects are humans’ inferior ears, spine, and lungs. Roberts borrowed anatomy from reptiles, birds, and other mammals to create a Frankenstein-esque creature straight from the island of Dr. Moreau.

The sculpture of Alice 2.0, left, with Alice Roberts, right
Courtesy of October Films

The sculpture has legs like an ostrich because, as Roberts says on her website, the human knee is complex and prone to failure. Like humans, ostriches are bipedal, but they are far better runners. Bird-like lungs that keep air flowing in one direction, not two, make running and other aerobic activities easier for the perfect human to manage. And a chimpanzee’s sturdier spine and a dog’s heart (which has more connected arteries, leading to lower heart attack risk) make Roberts’s alternate self more resistant to injury and disease.

Roberts’s ideal human body also has skin like a frog that can change shades based on the environment, and large, bat-like ears that amplify sound. Roberts also fixed humans’ backwards retina, which produces a natural blind spot, by borrowing from octopus eye anatomy.

Perhaps most disturbing of all is the baby head poking out of the sculpture’s marsupial pouch. Roberts says marsupial pregnancy would be far easier on the human body and more convenient for parents on the go.

“This could be a human fit for the future,” Roberts says at the end of a trailer for her BBC documentary.

[h/t Motherboard]

nextArticle.image_alt|e
iStock
Scientists Accidentally Make Plastic-Eating Bacteria Even More Efficient
iStock
iStock

In 2016, Japanese researchers discovered a type of bacteria that eats non-biodegradable plastic. The organism, named Ideonella sakaiensis, can break down a thumbnail-sized flake of polyethylene terephthalate (PET), the type of plastic used for beverage bottles, in just six weeks. Now, The Guardian reports that an international team of scientists has engineered a mutant version of the plastic-munching bacteria that's 20 percent more efficient.

Researchers from the U.S. Department of Energy's National Renewable Energy Laboratory and the University of Portsmouth in the UK didn't originally set out to produce a super-powered version of the bacteria. Rather, they just wanted a better understanding of how it evolved. PET started appearing in landfills only within the last 80 years, which means that I. sakaiensis must have evolved very recently.

The microbe uses an enzyme called PETase to break down the plastic it consumes. The structure of the enzyme is similar to the one used by some bacteria to digest cutin, a natural protective coating that grows on plants. As the scientists write in their study published in the journal Proceedings of the National Academy of Sciences, they hoped to get a clearer picture of how the new mechanism evolved by tweaking the enzyme in the lab.

What they got instead was a mutant enzyme that degrades plastic even faster than the naturally occurring one. The improvement isn't especially dramatic—the enzyme still takes a few days to start the digestion process—but it shows that I. sakaiensis holds even more potential than previously expected.

"What we've learned is that PETase is not yet fully optimized to degrade PET—and now that we've shown this, it's time to apply the tools of protein engineering and evolution to continue to improve it," study coauthor Gregg Beckham said in a press statement.

The planet's plastic problem is only growing worse. According to a study published in 2017, humans have produced a total of 9 billion tons of plastic in less than a century. Of that number, only 9 percent of it is recycled, 12 percent is incinerated, and 79 percent is sent to landfills. By 2050, scientists predict that we'll have created 13 billion tons of plastic waste.

When left alone, PET takes centuries to break down, but the plastic-eating microbes could be the key to ridding it from the environment in a quick and safe way. The researchers believe that PETase could be turned into super-fast enzymes that thrives in extreme temperatures where plastic softens and become easier to break down. They've already filed a patent for the first mutant version of the enzyme.

[h/t The Guardian]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios