The extinction of the dinosaurs, creatures that had ruled Earth for 180 million years, perplexed scientists for decades. It was the ultimate murder mystery.
In the 1990s, a theory that an asteroid hit the Earth and killed almost all plant and animal life was confirmed by the discovery of a gigantic crater, partly buried under the Yucatan Peninsula in eastern Mexico and partly under the sea.
The dinosaurs’ nemesis had indeed come from the stars. The asteroid had struck at a place called Chicxulub, which means ‘tail of the Devil’.
Now, thanks to a scientific survey of the crater’s rim by a team led by Sean Gulick, a marine geophysicist from the University of Texas, and reported last month in the U.S. journal Proceedings of the National Academy of Sciences, we have a far deeper understanding of the timeline of events that occurred when the asteroid hit, as the Mail now reveals.
The extinction of the dinosaurs, creatures that had ruled Earth for 180 million years, perplexed scientists for decades. It was the ultimate murder mystery
Two days to impact
Sixty-six million years ago, in the night sky above Earth, a small bright light has appeared. It doesn’t seem to be moving but it is getting brighter. The object is a massive asteroid, nine miles wide and travelling at phenomenal speed.
Directly in its path is the Earth.
Our planet is in what scientists call the Cretaceous period, a time of tropical temperatures. Thanks to seasonal rainfall, there is abundant life. Roughly a third of Earth’s present land area, including all of what is now Britain, lies under shallow seas. Although much of Europe is covered by water, the continents otherwise look similar to how they are today. They have been moving apart at the speed a fingernail grows — and as they separated, dinosaurs evolved independently on each land mass, becoming more diverse.
One hour to impact
The last day of the Cretaceous period begins like any other. The land is covered with forests and flowering plants, pollinated by insects; the seas are full of fast predatory fish such as the fanged xiphactinus and 46ft-long tylosaurus. In the air, species of bird such as ornithocheirus glide majestically.
Land dinosaurs have colonised the whole planet and include terrifying creatures such as Tyrannosaurus rex and Giganotosaurus. If they look up, these creatures can see what appear to be two Suns. The strange new orb southeast of what is now Mexico is getting larger all the time, as Earth’s gravitational pull causes it to accelerate.
Two minutes to impact
The asteroid zooms over the South Atlantic at a shallow angle, burning at 20,000 degrees Celsius. It is now many times brighter than the Sun. It looks like a fireball.
Five seconds to impact
Travelling at 45,000 miles an hour, the asteroid enters Earth’s atmosphere, blasting a hole in it. This sets off a global supersonic shockwave and a creates a flash of light so blinding that shadows of trees, plants and dinosaurs are etched in silhouette on the scorched ground.
One hundred and fifty million years of evolution is about to end.
The asteroid smashes into the shallow waters of what is now the Yucatan Peninsula, creating a crater 100 miles across and 20 miles deep. In an instant, the asteroid is vaporised. Twenty-five trillion tons of debris rocket into the atmosphere — enough to cover the entire globe.
The explosion is equal to 100 trillion tons of TNT and a billion times more powerful than the Hiroshima bomb. In the impact crater, a peak higher than Everest rises before falling back.
In the 1990s, a theory that an asteroid hit the Earth and killed almost all plant and animal life was confirmed by the discovery of a gigantic crater, partly buried under the Yucatan Peninsula in eastern Mexico and partly under the sea
One minute after impact
The blast sends molten material into the atmosphere at speeds of more than 100,000 miles an hour. Some of it will hit the Moon.
Because of the shallow angle of its trajectory, most of the asteroid’s destructive power is thrown forward. The burning debris fanning out from the Chicxulub crater is hotter than the surface of the Sun and ignites everything within a thousand-mile radius.
The temperature rises to more than 300c and the water in the skin of any dinosaur close to the impact starts to boil, then burst out as steam.
Creatures are incinerated in an instant: thousands of 50ft-long lambeosaurus, with their brightly coloured heads; sarcosuchus, the giant crocodile that itself feeds on dinosaurs; and the heaviest of them all, argentinosaurus, which weighs up to 100,000kg (16,000st). All are burnt alive.
A tsunami hundreds of feet high radiates from the crater. Countless thousands of sea creatures are caught in the maelstrom — starfish, sea urchins, heavy-shelled turtles, aquatic lizards known as eupodophis and 40ft hydrotherosauruses. Some of these creatures are still alive but many are already dead.
Two minutes after impact
Some of the larger pieces of rock ejected by the explosion begin falling back to earth, creating further enormous craters and starting more wildfires.
Seismic waves radiate down through the core of the planet. As the ground leaps and buckles, large dinosaurs tumble over but smaller creatures fare better.
The little long-snouted zalambdalestes, early mammals, burrow for safety. Eight-inch-long cimolestes, whose name means ‘insect thief’, are also seeking shelter in the ground and under rocks (cats and dogs are descended from this clever survivor).
Three minutes after impact
Just over 2,000 miles north of the impact zone, in what is now Hell Creek, Montana, a group of Tyrannosaurus rexes, the biggest meat-eaters, are heading through a conifer forest to a riverbank.
The six-ton creatures tower nearly 40ft high. Suddenly, the ground beneath their gigantic hind legs starts to rise and fall.
Smaller creatures are smashed against trees — then the mighty Tyrannosaurus rexes stagger and fall, smashing their skulls.
The corpses of hundreds of creatures are eventually buried in the shifting sediments. Sixty-six million years later, the discovery of their remains will provide vital evidence about the asteroid strike.
Five minutes after impact
Flying above North America are flocks of quetzalcoatlus, a dinosaur with a 36ft wingspan that uses thermal currents to stay airborne for hours.
Because it is vulnerable to predators, the quetzalcoatlus, like the modern albatross, rarely lands.
Its dominance of the skies is about to end.
Molten rock flung high into the air is cooling as it falls, creating small glass ‘bullets’ known as tektites. These puncture the wings of the quetzalcoatluses, and one by one they start falling from the sky. In Hell Creek, Montana, red-hot tektites thump into the dying Tyrannosaurus Rexes, burning holes in their skin.
30 minutes after impact
Travelling at more than 100 miles an hour, the tsunami hits coastlines, ripping up tons of rocks and hurling them inland, extinguishing forest fires as it barrels forward.
Giant trees and the corpses of fish and marine dinosaurs are carried in the wave and, as the water eventually slows, are deposited far inland. Meanwhile, on the northeastern rim of the Chicxulub crater, seawater is starting to cascade down its steep walls.
The lethal hailstorm of tektites finally ends.
Three hours after impact
Across North America, wildfires are still burning but the air is steadily cooling now the tektites and molten rocks have ceased.
In Montana, there is suddenly a deafening sonic boom — it is the sound of the asteroid hitting Earth 2,000 miles away, and has taken that long to travel the distance northward. The noise ruptures the ears of those dinosaurs still alive.
Four hours after impact
As the world turns, the fiery cloud spreads around the globe. It is charged with millions of volts of static electricity, creating spectacular electrical storms. Across the planet, landslides and earthquakes caused by the blast lead to further tsunamis.
Now the effects of the asteroid strike are reaching the islands and seas that will one day become Western Europe. Here, the earth is shaking and wildfires have been ignited across the land.
Plants including magnolias, sassafras, gingkoes and cycads are swallowed by the flames.
The biggest land animals ever, the sauropods, are fighting for life. The herbivore iguanodon, one of the most successful dinosaurs of its day, with a thumb in the shape of a defensive spike, finds itself as helpless as all the others in the face of this catastrophe.
Five hours after impact
In the Gulf of Mexico, the first of numerous super-tsunamis that have bounced off coastlines starts to batter the rim of the Chicxulub crater. Thousands of tons of water topple down its sides.
Six hours after impact
All the forests on the Indian sub-continent, 9,000 miles from the crater, are ablaze. In the deserts of southern Mongolia, large ostrich-like citipati are sitting on clutches of eggs, their feathered arms spreading to the edges of their nests to protect the eggs from the sun.
Here there are no fires but for the past few hours the temperature has been rising alarmingly. The citipati are slowly being cooked alive.
Ten hours after impact
In North America, it is cooler but the air is still thick with smoke from wildfires. Countless herds of triceratops, horned creatures the size of elephants, that had been feeding happily in swamps, are dead or dying. The high-walled nests of the females, each containing between 15 and 20 eggs hidden under conifer branches, lie abandoned.
One day after impact
The sun has not reappeared. Soot and dust block its light.
This is the first day of what palaeontologists call the Cenozoic or ‘recent’ era.
Debris from the crater is still heading into space at high speed. Within weeks, some of it will be orbiting the Sun. Fragments will eventually land on Mars and on the moons of Saturn and Jupiter. This debris may contain living microbes and so have exported life from Earth into space.
Now we have a far deeper understanding of the timeline of events that occurred when the asteroid hit
One week after impact
The sky is still dark. Photosynthesis has been suspended and plants are dying. Any large herbivores that survived the effects of the impact, such as the sauropods, horned ceratopsians and the duck-billed hadrosaur, are starting to starve.
In the oceans, the once-teeming, photosynthesising plankton have died, so the fish that feed on them have also perished. Giant reptiles such as the crocodile-toothed mosasaurus will soon run out of dead fish to feed on.
Two weeks after impact
The remaining meat-eating dinosaurs are starving, deprived of their prey. However, one type — the avian dinosaurs known as birds — are showing signs that they may survive the apocalypse.
Their ability to fly means some have been able to escape and find less harsh conditions — and as small creatures breed faster than large ones, they will adapt faster to new environments.
Birds don’t need to eat as much as larger animals, and may be able to survive on insects and seeds that remain hidden in the soil.
These survivors will evolve over millions of years into birds we know today, such as penguins, owls and ducks. In the sea, turtles and crocodiles, able to eat decaying plants, have also survived.
Two months after impact
The fires have died down and the Earth is cold and dark. Dust still prevents any sunlight reaching the planet’s surface. The darkness will last for two more months.
Seventy per cent of Earth’s forests have been destroyed and 75 per cent of all species annihilated. Any animal larger than a crocodile has been wiped out.
Acid rain is falling and the atmosphere is full of billions of tons of carbon dioxide, methane and carbon monoxide. These greenhouse gases were released when layers of limestone were vaporised in the impact crater.
The world is quieter without the marauding dinosaurs. No longer will the velociraptor tear into its prey with serrated teeth, or the horned carnotaurus bludgeon animals to death.
The reign of the lizards is over.
Scientists believe that if the asteroid had fallen just a few minutes later, the fate of our planet would have been very different. An impact in deeper water, after the Earth had turned, would have meant much of the force was absorbed, resulting in less intense firestorms and a smaller quantity of rock being flung into the atmosphere.
After the dinosaurs…
As one world ends, another begins. The dust clears and sunlight begins to warm the Earth. Plant life eventually recovers.
Within a few hundred thousand years, the world is again covered by swamps and jungles.
The demise of the dinosaurs has given mammals, hitherto insignificant, an opportunity to expand in number and variety.
Mammals had long lived in the shadow of the dinosaurs but now their time has come. The ancestors of elephants, rodents, bats and whales start to appear — and so does our own distant ancestor, the earliest primate.
Without the asteroid, none of us would be here.
Jonathan Mayo is the author of D-Day: Minute by Minute (Short Books)