How do scientists know that a meteorite killed the dinosaurs?
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Fossils and dating shows a very clear line when they stopped existing. That points to a global event that had to happen. The only global event that we can come up with is a meteorite that is large enough. And then we found the crater. Case closed 🙂
They don’t. We have evidence of a giant asteroid strike in the Yucatan region of Mexico 65 million years ago that spread debris across the whole planet. Dinos vanished within 150 million( edit–150 thousand–sorry) years after. (A blink of an eye in geological records) Also, giant volcanos in Mongolia and Asia filled the air with ash around the same time period. It may have been a one-two punch that removed enough large dinos so that mammals could take over the new habitats made available. Most scientists agree the dust clouds from either event blocked out enough sun to remove most trees from the food chain and small seed storing mammals underground had the best chance of survival during the years after it took for the dirty air to let sunlight reach the ground. This is called nuclear winter.
“Know” is a strong word in science. We look at the evidence, form a hypothesis, and test it against the observations. We have a lot of evidence that a meteorite hit the Earth approximatley 65MYA and we also have a lot of evidence that the dinosaur fossils start disappearing rapidly around that same time. We don’t have video footage of the meteor impacting the planet and we don’t have precise census-data of dinosaurs, but we make the best with what we have.
https://en.wikipedia.org/wiki/Chicxulub_crater
What everyone else is missing is the stratas of geological digs going back millions of years. Core samples in differing regions of the world indicate many things happening over the course of that region’s life. Core samples can show periods of heavy plant life, heavy drought, ice ages, so many things.
Other people have given very good answers but I should note that not all the dinosaurs died and that certain lineages survived and are now what we call birds. You’ll often hear people try to say that birds aren’t dinosaurs but are DESCENDANTS of dinosaurs, but that distinction is totally meaningless in biology.
Just like you, a human being, are a member of the Great Apes which are members of the primates which are members of the mammals, birds are members of the maniraptorans which are members of the theropods which are members of the dinosaurs.
Just to add, it’s not like the meteorite hit and all the dinosaurs dropped dead. It took probably hundreds if not thousands of years for it to happen. The meteorite didn’t kill the dinosaurs it just started a long chain of reactions that eventually led to most dinosaurs dying.
The short answer is that there is a huge crater in Mexico and geologists can tell that it appeared approximately 66 million years ago. Fossils stopped appearing shortly after.
The slightly longer answer is that an asteroid the size of the crater in Mexico hitting the earth would create a shockwave which would release energy equivalent to billions of atomic bombs. The debris and soot from the impact blocked sunlight, leading to a “nuclear winter” effect. This caused a dramatic drop in temperatures and disrupted photosynthesis, which affected the food chain. Plants died off or were severely diminished, leading to the collapse of herbivore populations and, subsequently, predator species that depended on them. The combination of these factors led to long-term environmental changes, making it difficult for many species, including dinosaurs, to survive.
This is a really fucking cool article about paleontologist Robert DePalma and his dig site that he believes is a record of time from when the asteroid hit: https://www.newyorker.com/magazine/2019/04/08/the-day-the-dinosaurs-died
https://www.science.org/doi/10.1126/sciadv.abe3647
There is a layer in the sediment dating back 66.05 million years. That layer is super rich in iridium. There are large dinosaur fossils below that layer, but none found above it.
An iridium layer found all over the planet from exactly the same time can only be caused by a few events. The most probable is an asteroid impact.
In the 1990s the Chicxulub crater was suspected as the impact site, and in 2021 it was confirmed as the source of the iridium layer that marks the end of the dinosaurs.
Right around the extinction event 65 MYA, there’s a very thin layer of dust in the rock layers containing elements like iridium that are consistent with meteorite impacts. Since this layer is found almost everywhere on Earth, this meteorite impact must have been a big one.
We also located the crater of this impact in the Yucatan Peninsula dating back to the same age. It’s big and old, big enough and old enough to meet the criteria for the asteroid that killed the dinosaurs.
New research indicates, however, that the meteorite may not have been the cause of the mass extinction, but rather just happened to occur around the same time. The other mass extinction events have been tied to a supervolcano eruption, and there is also evidence for this happening about 65 MYA, and it fits the pattern of the other extinction events.
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