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March 1 - March 9, 2025
Descriptions of the doom and gloom could go on for pages, but the point is, the end of the Permian was a very bad time to be alive. It was the biggest episode of mass death in the history of our planet. Somewhere around 90 percent of all species disappeared.
Caused by a runaway greenhouse effect killing the conifer forests and turning the oceans to acid.
But to end up with these as fossils, we need to be very lucky: the animal needs to be buried so quickly that these fragile tissues don’t have time to decay or get eaten by predators.
The Earth formed about 4.5 billion years ago, and the first microscopic bacteria evolved a few hundred million years later. For some 2 billion years, it was a bacterial world. There were no plants or animals, nothing that could easily be seen by the naked eye, had we been around.
The first true dinosaurs arose some time between 240 and 230 million years ago.
Herrerasaurus was one of the very first theropod dinosaurs—a founding member of that dynasty of smart, agile predators that would later ascend to the top of the food chain and ultimately evolve into birds.
Secondly, they need to grow fast. Growing bit by bit, year by year is all well and good, but if it takes you over a century to get big, that’s many opportunities for a predator to eat you, or a tree to fall on you during a storm, or a disease to take you out long before you grow into your full-size adult body.
And because both a large tyrannosaur like Yutyrannus and a small tyrannosaur like Dilong have feathers, this implies that the common ancestor of all tyrannosaurs had feathers, and therefore that the great T. rex itself was most likely feathered, too.
T. rex was agile and energetic, and it moved with purpose, its head and tail balancing each other as it tiptoed through the trees, stalking its prey. But its maximum speed was probably in the ballpark of ten to twenty-five miles per hour. That’s faster than we can run, but it’s not as quick as a racehorse or, certainly, a car on the open road.
T. rex was simply too big to run exceptionally fast. Its sheer size also conferred another liability: the Tyrant King couldn’t turn very quickly, or otherwise it would topple over like a truck taking a corner too sharply. Thus, the reality is, Spielberg had it wrong, T. rex was no sprinter, and it would have ambushed its prey with a quick strike rather than chasing it down like a cheetah.
Seagulls, and all other birds, evolved from dinosaurs. That makes them dinosaurs. Put another way, birds can trace their heritage back to the common ancestor of dinosaurs, and therefore are every bit as dinosaurian as T. rex, Brontosaurus, or Triceratops,
Huxley agreed that Archaeopteryx was a transitional fossil, linking reptiles and birds, but he went one step further. He noticed that it bore an uncanny resemblance to another fossil discovered in the same lithographic limestone beds in Bavaria, a small flesh-eating dinosaur called Compsognathus. So he proposed his own radical new idea: birds descended from dinosaurs.
After all, because birds evolved from dinosaurs, and because the half-dinosaur half-bird Archaeopteryx was found covered in fossilized feathers, feathers must have developed somewhere along their evolutionary lineage—maybe in a dinosaur long before birds came onto the scene.
These dinosaurs had the great misfortune to live in a dense forest surrounding a wonderland of ancient lakes, a landscape that was periodically obliterated by volcanoes. Some of these eruptions spewed out tsunamis of ash, which combined with water to flood the landscape in a viscous ooze that buried everything in sight. The dinosaurs were captured going about their everyday business, preserved Pompeii-style. That’s why the details of the feathers are so pristine.
And then they witnessed what came next, the instant that snuffed out almost all of the dinosaurs, all but a few of the most advanced, best-adapted, best-flying birds, which made it through the carnage and are still with us today—among them the seagulls outside my window.
Forests spontaneously ignited and wildfires swept across the land. The surviving animals were now roasting, their skin and bones cooking at temperatures that instantaneously produce third-degree burns. It was no more than fifteen minutes since the T. rex pack was startled by that first jolt of light, but by now they were all dead, as were most of the dinosaurs they had lived with.
Other places, though, had it much worse. Much of the mid-Atlantic coast was sliced apart by tsunamis twice as tall as the Empire State Building, which flushed the carcasses of plesiosaurs and other sea-dwelling giant reptiles far inland. Volcanoes started to spew out rivers of lava in India. And a zone of Central America and southern North America—everything within a radius of about six hundred miles (one thousand kilometers) of the Yucatán Peninsula of modern-day Mexico—was annihilated. Vaporized.
Some did stagger on, however, into the next day, the next week, the next month, the next year, and the next decades. It was not an easy time. For several years after that terrible day, the Earth turned cold and dark because soot and rock dust lingered in the atmosphere and blocked out the sun.
A comet or an asteroid—we aren’t sure which—collided with the Earth, hitting what is now the Yucatán Peninsula of Mexico. It was about six miles (ten kilometers) wide, or about the size of Mount Everest.
When it slammed into our planet, it hit with the force of over 100 trillion tons of TNT, somewhere in the vicinity of a billion nuclear bombs’ worth of energy.
All creatures living within six hundred miles (a thousand kilometers) or so of the Yucatán would have been instantly turned into ghosts.
This rock was softer, finer; it was a layer of clay, about one centimeter thick, a bookmark separating the limestones of the Cretaceous below from those of the postextinction Paleogene period above. It was here—this man, standing at this spot, looking at this strip of clay—where the asteroid theory was conceived a quarter century earlier.
Some of the rocks he was measuring were crammed with fossil shells of all shapes and sizes, which belonged to a great diversity of creatures called forams—tiny predators that float around in the ocean plankton. Above these rocks, however, were nearly barren limestones, sprinkled with a few tiny, simple-looking forams.
Heavy metals—some of those elements in the nether regions of the periodic table, like iridium—are rare on Earth’s surface, which is why most people have never heard of them. But tiny amounts of them fall at a more or less constant rate from the deep reaches of outer space as cosmic dust. The Alvarezes reasoned that if the clay layer had only a tiny peppering of iridium, then it had formed very quickly; if it had a larger amount, then it must have formed over a much longer time period. New instruments now allowed scientists to measure even very small concentrations of iridium, including one in
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Iridium is super-rare on Earth but much more common in outer space. Could something from the deep expanses of the solar system have delivered an iridium bomb 66 million years ago?
Then, as the 1990s dawned, the crater was finally found. The smoking gun. It had taken a while to find it because it was buried under millions of years of sediment in the Yucatán. The only detailed studies of the area had been carried out by oil-company geologists who kept their maps and samples locked up for many years. But there could be no doubt: the 110-mile-wide (180 km) hole buried under Mexico, called the Chicxulub crater, was dated right to the end of the Cretaceous, 66 million years ago.
Instead, we found that there is no doubt about it: the dinosaur extinction was abrupt, in geological terms. This means that it happened over the course of a few thousand years at most. Dinosaurs were prospering, and then they simply disappear from the rocks, simultaneously all over the world, wherever latest Cretaceous rocks are known.
Why did all the non-bird dinosaurs die at the end of the Cretaceous? After all, the asteroid didn’t kill everything. Plenty of animals made it through: frogs, salamanders, lizards and snakes, turtles and crocodiles, mammals, and yes, some dinosaurs—in the guise of birds.
It’s estimated that some 70 percent of species went extinct. That includes a whole lot of amphibians and reptiles and probably the majority of mammals and birds, so it’s not simply “dinosaurs died, mammals and birds survived,”
Turtles and crocodiles fared pretty well compared to other vertebrates, and that is probably because they were able to hide out underwater during those first few hours of bedlam, shielding themselves from the deluge of rock bullets and the earthquakes.
We humans now wear the crown that once belonged to the dinosaurs. We are confident of our place in nature, even as our actions are rapidly changing the planet around us. It leaves me uneasy, and one thought lingers in my mind as I walk through the harsh New Mexican desert, seeing the bones of dinosaurs give way so suddenly to fossils of Torrejonia and other mammals. If it could happen to the dinosaurs, could it also happen to us?
