No species lasts forever — extinction is part of the evolution of life.
But at least five times, a biological catastrophe has engulfed the planet, killing off the vast majority of species from water and land over a relatively short geological interval.
The most famous of these mass extinction events — when an asteroid slammed into Earth 66 million years ago, dooming the dinosaurs and many other species — is also the most recent. But scientists say it won’t be the last.
Many researchers argue we’re in the middle of a sixth mass extinction, caused not by a city-size space rock but by the overgrowth and transformative behavior of a single species— Homo sapiens. Humans have destroyed habitats and unleashed a climate crisis.
Calculations in a September study published in the journal PNAS have suggested that groups of related animal species are disappearing at a rate 35% times higher than the normally expected rate.
And while every mass extinction has winners and losers, there is no reason to assume that human beings in this case would be among the survivors.
In fact, study coauthor Gerardo Ceballos thinks the opposite could come to pass, with the sixth mass extinction transforming the whole biosphere, or the area of the world hospitable to life — possibly into a state in which it may be impossible for humanity to persist unless dramatic action is taken.
“Biodiversity will recover but the winners (are) very difficult to predict. Many of the losers in these past mass extinctions were incredibly successful groups,” said Ceballos, a senior researcher at the Institute of Ecology at the National Autonomous University of Mexico.
While the causes of the “big five” mass extinctions varied, understanding what happened during these dramatic chapters in Earth’s history — and what emerged in the aftermath of these cataclysms — can be instructive.
“Nobody’s seen these events but they’re on a scale that might be repeated. We’ve got … (to) learn from the past because that’s our only data set,” said Michael Benton, a professor of vertebrate paleontology at Bristol University in the United Kingdom who is the author of the new book “Extinctions: How Life Survives, Adapts and Evolves.”
A really bad day: Dino-killing asteroid and the iridium anomaly
While paleontologists have studied fossils for centuries, the science of mass extinction is relatively new. Radiometric dating, based on the natural radioactive decay of certain elements, like carbon, and other techniques revolutionized the ability to precisely determine the age of ancient rocks in the second half of the last century.
The developments set the stage for the work of the late Nobel Prize-winning physicist Luis Alvarez and his geologist son Walter, professor of Earth and planetary science at the Univeristy of California, Berkeley. Along with two other colleagues, they coauthored a sensational 1980 paper about the “iridium anomaly” — a 1-centimeter-thick (0.4-inch-thick) layer of sedimentary rock rich in iridium, an element rare on Earth’s surface but common in meteorites.
The researchers attributed the anomaly, which they initially identified in Italy, Denmark and New Zealand, to the impact of a large asteroid. They argued the unusual layer represented the exact moment in time when dinosaurs disappeared.
First met with skepticism, the iridium anomaly eventually was spotted in more and more places around the world. A decade later, a different group of researchers identified the smoking gun: a 200-kilometer-wide (125-mile-wide) crater off the coast of Mexico’s Yucatan Peninsula.
The rock and sediment there had a similar composition to the iridium layers, and the scientists suggested the depression, called the Chicxulub crater, was caused by the impact of an asteroid. Researchers believe the other anomalies spotted across the globe were caused by scattering debris when the space rock struck Earth.
The late physicist Luis Alvarez (left) and Walter Alvarez, professor of Earth and planetary science at the University of California, Berkeley, view a sample of an iridium layer deposit. Based on this layer, the father-and-son research team postulated in a 1980 study that a giant asteroid hit Earth in the Cretaceous Period.
Roger Ressmeyer/Corbis/VCG/Getty Images
Most paleontologists now accept that the asteroid caused what’s known as the end-Cretaceous extinction. The strike triggered a period of global cooling, with dust, soot and sulfur thrown up during the impact blocking the sun and likely shutting down photosynthesis, a key process for life.
One fossil site in North Dakota has provided an unprecedented level of detail on what that day — and its immediate aftermath — was like. Debris rained down, lodging itself into the gills of fish, while huge tsunami-like surges of water unleashed by the strike killed dinosaurs and other creatures. Scientists have even figured out that the asteroid smashed into Earth in springtime.
The disappearance of massive dinosaurs created a world in which mammals — and ultimately humans — were able to thrive. And dinosaurs weren’t the total losers they are sometimes made out to be: Scientists now believe that the birds that flap around in our backyards directly evolved from smaller relatives of Tyrannosaurus rex.
In the wake of the Alvarez duo’s stunning discovery, it initially seemed to scientists as ifa space rock impact might be a general mechanism that explained all massextinction events identified in the geological record. But the end-Cretaceous extinction is the only one reliably associated with an asteroid, according to Benton.
A different culprit, however, does explain several smaller extinction episodes and at least two mass extinctions, including the largest on record.
Apocalyptic volcanoes that caused global warming
Something known as a hyperthermal event — a sudden warming of the planet — spelled doom for large segments of life on Earth on more than one occasion. These events have followed a predictable pattern: volcanic eruption, carbon dioxide release, global warming, acid rain, ocean acidification — resulting in a longer road to oblivion than the dino-killing asteroid but equally destructive.
The biggest mass cataclysm of all time, called the end-Permian extinction, occurred 252 million years ago. Some 95% of species disappeared on land and at sea as a result of global warming — with temperatures rising perhaps 10 degrees Celsius to 15 degrees Celsius (18 F to 27 F), Benton noted in his book.
Known as “the Great Dying,” the extinction event was marked by supervolcanic eruptions that expelled greenhouse gases in an Australia-size region known as the Siberian Traps in Eurasia. That led to extreme acid rain that killed plant life and left the land surface rocky as the precipitation washed rich soil into the oceans, which in turn became swamped with organic matter, Benton explained.
However, into the void that followed emerged different creatures that evolved from the survivors, displaying many new ways of existence with features such as feathers, hair and speedy locomotion, Benton said.
“One of the big changes … on land, it seems, was a great rise in energy of everything,” he explained. “All of the surviving reptiles very rapidly became upright in posture instead of (low and) sprawling. (Some animals) became warm blooded in some way because we track feathers back to the early Triassic dinosaurs and their nearest relatives, and on the mammals side, we track the origin of hair.”
Workers load supplies for the the L/B Myrtle offshore support vessel, part of a 2016 scientific mission led by the International Ocean Discovery Program to study the Chicxulub impact crater on the Gulf of Mexico. The crater was formed after an asteroid hit Earth 66 million years ago.
Ronaldo Schemidt/AFP/Getty Images
When dinosaurs got big
Another period of extreme volcanic activity 201 million years ago marked the end-Triassic mass extinction. It has been linked to the breakup of the Pangea supercontinent and the opening of the central Atlantic Ocean. Many land reptiles vanished as a result of that catastrophic event, making way for the towering sauropods and armored plant eaters commonly seen in childhood dinosaur books.
“The dinosaurs were already around but they had not fully diversified,” Benton said. “And then in the early Jurassic, … the dinosaurs really took off.”
Deeper in time, a mass extinction event that ended the Devonian Period, a geological era when life thrived on land for the first time, was also attributed to a hyperthermal eventlikely triggered by volcanic activity 359 million years ago, according to Benton’s book.
Other research published in 2020 suggested that multiple star explosions — known as supernovae — may have played a role.
A less well-understood period of worldwide cooling soon followed. It’s thought that these twin crises — separated by only 14 million years — led to rapid changes in temperature and sea level that resulted in the loss of at least 50% of the world’s species, wiping out many armored fish, early land plants, and animals such as the fishapods, or the earliest elpistostegalians, that were making the transition from water to land.
The resulting loss of marine species made way for the golden age of sharksduring the Carboniferous Period, when the predators dominated the seas and evolved to include a variety of species with different forms.
The Siberian Traps was a vast area of volcanic activity in Eurasia that led to the biggest mass extinction 252 million years ago. The distant mountains are remains of basalt lava flows, and the Maymecha river can be seen amid the thick volcanic layers. The foreground is also the rubbly top of the volcanic landscape.
Benjamin Black/US Geological Survey
Sinking temperatures and sea levels
Colder temperatures and a drastic drop in sea levels — perhaps as much as 10 degrees Celsius (18 F) cooler and 150 meters (492 feet) lower, respectively — played a major role in the earliest identified mass extinction event, the end-Ordovician, according to Benton. That shift, which took place about 444 million years ago, led to the disappearance of 80% of species at a time when life was mostly limited to the seas.
What triggered the die-off was the massive Gondwana supercontinent (today’s South America, Africa, Antarctica and Australia) drifting over the South Pole during the Ordovician. When a land mass covers the polar region, the ice cap reflects sunlight and slows melting, resulting in an expanding ice cap that lowers sea levels globally.
Adding to the cataclysm was volcanic activity. However, in this case, it did not appear to make global temperatures warmer. Instead, phosphorus from lava and volcanic rocks washed into the sea, gobbling up life-giving oxygen from the oceans.
The looming sixth mass extinction
A growing number of scientists believe a sixth mass extinction event of a magnitude equal to the prior five has been unfolding for the past 10,000 years as humans have made their mark around the globe.
The dodo, the Tasmanian tiger, the baiji, or Yangtze River dolphin, and the Western black rhino are just a few of the species that have disappeared so far in what’s known as the Holocene or Anthropocene extinction.
While the loss of even one species is devastating, Ceballos of the National Autonomous University of Mexico has highlighted that the ongoing episode of extinction is mutilating much thicker branches of the tree of life, a metaphor and model that groups living entities and maps their evolutionary relationships.
Entire categories of related species, or genera, are disappearing, a process he said is affecting whole ecosystems and endangering the survival of our own species.
Ceballos and his study coauthor Paul Ehrlich, Bing Professor Emeritus of Population Studies at Stanford University, assessed 5,400 genera of vertebrate animals, excluding fishes. A single genus groups one or more different but related species — for example the genus Canis includes wolves, dogs, coyotes and jackals.
The duo’s analysis found that 73 genera had gone extinct in the past 500 years. This is much faster than the expected “background” extinction rate, or the rate at which species would naturally die off without outside influence — in the absence of human beings, these 73 genera would have taken 18,000 years to vanish, the researchers said.
The causes of these extinctions are varied — land-use change, habitat loss, deforestation, intensive farming and agriculture, invasive species, overhunting and the climate crisis — but all these devastating changes have a common thread: humanity.
Specimens of the extinct dodo bird are seen on display in London’s Natural History Museum.
Kevin Foy/Alamy Stock Photo
Ceballos pointed to the extinction of the passenger pigeon, which was the only species in its genus, as an example of how losing a genus can have a cascading effect on a wider ecosystem. The bird’s loss, a result of reckless hunting in the 19th century, narrowed human diets in eastern North America and allowed the bacteria-harboring White-footed mice that were among its prey to thrive.
What’s more, some scientists believe the passenger pigeon’s extinction, combined with other factors, is behind today’s rise of tick-borne diseases such as Lyme disease that plague humans and animals alike, according to the study.
Not only do the destructive actions of humans have the potential to erode our quality of life in the long term, but their ripple effects could eventually upend our success as a species, according to Ceballos.
“When we lose genera, we’re losing more genetic diversity, we’re losing more evolutionary history, and we’re losing (many) more ecosystem goods and services that are very important,” he explained.
While branches of the tree of life are vanishing, the distribution of certain animal species is becoming more homogenized —the world is home to about 19.6 billion chickens, 980 million pigs and 1.4 billion cattle. In some cases, intensive farming can trigger outbreaks of disease like avian influenza outbreaks that rip through poultry farms and increase risk of spillover in wild migratory birds. Other farm animals act as hosts for virus that infect humans, with the potential to cause pandemics like Covid-19.
Ultimately, the planet can and will survive just fine without us, Ceballos added. But, like the iridium anomaly left by the dinosaur-dooming space rock, what might the final traces of human civilization look like in the geological record?
Some scientists point to the geochemical traces of nuclear bomb tests, specifically plutonium — a radioactive element widely detected across the world in coral reefs, ice cores and peat bogs.
Others say it could be something altogether more mundane, such as a fossilized layer of bones from chickens — the domesticated bird industrially bred and consumed across the world in mammoth quantities — that’s left as humanity’s defining legacy for the ages.
More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.
That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.
“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”
The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.
Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.
Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.
Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.
Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.
“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”
The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.
North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.
Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”
Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.
Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.
For Dello, the “fingerprints of climate change” were clear.
“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”
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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.
On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.
They call it “Big Sam.”
The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.
It didn’t die alone.
“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.
She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”
“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.
The head alone, she said, is about the size of a baby elephant.
The discovery was a long time coming.
The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.
“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.
When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”
“It contains about 100 to 300 bones per square metre,” she said.
Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.
About a year ago, they found the second adult: Big Sam.
Bamforth said both dinosaurs are believed to have been the elders in the herd.
“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.
“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”
The genders of the two adults are unknown.
Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.
The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.
She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.
“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.
“It’s pretty exciting.”
This report by The Canadian Press was first published Sept. 25, 2024.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
