Above: Imagination of an asteroid hitting the Earth.
This huge asteroid traveled through space, burned through the atmosphere and crashed into the earth.
Within 10 hour after the impact, a large-scale tsunami occurred along the coast of the impact point, which almost destroyed all life on the nearby land.
At the same time, the collision released a lot of dust, covering the whole planet and blocking the light from the sun.
Image above: Adult Tyrannosaurus Rex weighs between 6 and 9 tons and can reach 43 feet in length.
Without the sun, the source of life, almost all phytoplankton in the aquatic food chain were harvested, and then aquatic life was extinct on a large scale.
And there is no warm sunshine, which makes the surface temperature of the earth plummet. Life is difficult to adapt to drastic temperature changes, leading to further extinction.
The collision caused global climate change and a series of environmental damage, resulting in the disappearance of 75% animal and plant species including non-bird dinosaurs.
In the end, only in the shallow waters of the Gulf of Mexico, a Chicxulubo crater was left.
The extinction of dinosaurs paved the way for the rise of mammals and the final appearance of human beings, but what would life be like on earth if asteroids had not hit the earth 65 million years ago?
The answer is that there is no change, and there will be no so-called "dinosaur man" at all, because it is not asteroids that really extinct dinosaurs, but the earth.
This discovery comes from a new study published in Nature News on June 29th, 20021.
In fact, during the 6.5438+million years before the impact, dinosaurs were slowly dying out. Asteroids are just the last nail in the dinosaur coffin, pushing behind the endangered dinosaurs.
The researchers behind this new study studied the six richest dinosaur families that lived in the late Cretaceous: Ankylosauridae, Ceratosauridae, Duckbill, Celastraceae, Dinosauridae and Tyrannosaurus.
Including 247 species of dinosaurs, *** 1600 fossils, spanning 65438+45 million years ago to 66 million years ago.
The results show that dinosaurs have been evolving and expanding. However, 76 million years ago, that is, 6.5438+million years before the asteroid impact, the number of dinosaur species suddenly declined.
That is, their extinction rate is rising, while the emergence of new species is becoming less and less.
Above: The species formation rate (blue) of dinosaurs has decreased and the extinction rate (red) has risen sharply in the past 6.5438+million years. The total speciation rate (black) decreased.
The researchers noted that the decline of dinosaur species coincided with the drastic cooling of the global climate about 80 million years ago. It was in the late Cretaceous that the earth began to get colder. At that time, the global temperature dropped by about 7 degrees Celsius.
Therefore, the researchers speculate that considering that dinosaurs relied on the temperature of the environment to regulate the heat in their bodies, and dinosaurs had adapted to a warmer and wetter climate before, the drop in temperature was likely to bring trouble to the survival of large dinosaurs.
Then the research team added: There is a physiological hypothesis about dinosaurs.
If the sex determination of dinosaurs is like crocodiles and turtles, it has an unusual relationship with temperature. Then the sex change of dinosaur embryos may lead to the loss of diversity in the case of global climate cooling in the late Cretaceous.
At the same time, the research team found that there was a lag of 2 million years between the decline of carnivores and herbivores.
Therefore, another reason for the decrease of dinosaur species may be the decrease of herbivores in the ecosystem.
Moreover, in those 654.38+0 billion years, the hadrosaurs occupied a dominant position and spread all over the world. Its number far exceeds that of other herbivores, such as Triceratops and Ankylosaurus. So that other species have no food to eat, which is one of the reasons for the decline of other herbivore species.
The disappearance of herbivores makes the ecosystem unstable and prone to the cascade effect of extinction.
Above: Duckbilled Dragon that lived in Cretaceous.
The final conclusion is that the cold climate and the decrease of herbivores not only lead to the decline of dinosaur population, but also make the ecosystem lose its diversity, elasticity and fragility. In the end, every species can't recover after the impact.
For this subversive result, it is conceivable that there must be many voices of doubt.
Because fossil records are a difficult source of evidence, some people think that the gap and sampling deviation of dinosaur fossil records may lead to the omission of some Cretaceous dinosaur species.
However, the authors claim that their analysis method enables them to take into account some deviations in fossil data and the uncertainty of fossil age.
However, it is undeniable that except for birds, the extinction of half of animal and plant species occurred at the same time as the extinction of dinosaurs on land, so it is definitely not just declining creatures that were pushed to extinction by asteroid impact.
Extended reading
On June 26th, a batch of dinosaur footprints were found in Fushun, Zigong, Sichuan, including a tiny dinosaur footprint only 10.2mm long.
This footprint is the smallest dinosaur footprint recorded in China at present. It is speculated that the size of the small dinosaur that left footprints is about 12 cm long, which is roughly equivalent to the size of a modern sparrow.
Scholars tend to think that small footprints are left by newly born dinosaurs.
Related papers will be published in the journal Historical Biology.