- Biodiversity and natural selection
- Evidence for evolution
- Fossils: Rocking the Earth
- Molecular evidence for evolutionary relationships examples
- Carbon 14 dating 1
- DNA spells evolution
- Variation in a species
- Reproductive isolation
- Evidence for evolution
- Surviving an extinction level event
- Cellular evidence of common ancestry
- A brief history of mass extinctions
- Evidence of evolution
- Common ancestry and continuing evolution
A brief history of mass extinctions
Mass extinctions—when at least half of all species die out in a relatively short time—have happened a handful of times over the course of our planet's history. The largest mass extinction event occurred around 250 million years ago, when perhaps 95 percent of all species went extinct.
Top five extinctions
Ordovician-silurian Extinction: Small marine organisms died out. (440 mya)
Devonian Extinction: Many tropical marine species went extinct. (365 mya)
Permian-triassic Extinction: The largest mass extinction event in Earth's history affected a range of species, including many vertebrates. (250 mya)
Triassic-jurassic Extinction: The extinction of other vertebrate species on land allowed dinosaurs to flourish. (210 mya)
Cretaceous-tertiary Extinction: (65.5 mya)
65 million years ago: a mass extinction
Scientists refer to the major extinction that wiped out non-avian dinosaurs as the K-T extinction, because it happened at the end of the Cretaceous period and the beginning of the Tertiary period. Why not C-T? Geologists use "K" as a shorthand for Cretaceous. "C" is shorthand for an earlier period, the Cambrian.
The extinction that occurred 65 million years ago wiped out some 50 percent of plants and animals. The event is so striking that it signals a major turning point in Earth's history, marking the end of the geologic period known as the Cretaceous and the beginning of the Tertiary period.
Around 65 million years ago, something unusual happened on our planet—and we can see it in the fossil record. Fossils that are abundant in earlier rock layers are simply not present in later rock layers. A wide range of animals and plants suddenly died out, from tiny marine organisms to large dinosaurs.
Species go extinct all the time. Scientists estimate that at least 99.9 percent of all species of plants and animals that ever lived are now extinct. So the demise of dinosaurs like T. rex and Triceratops some 65 million years ago wouldn't be especially noteworthy—except for the fact that around 50 percent of all plants and animals alive at the same time also died out in what scientists call a mass extinction.
Changes in the environment
What happened to cause such widespread devastation 65 million years ago? Scientists agree that species go extinct primarily as a result of changes in their environment. The extinction of many species around the world at one time reflects large-scale changes in the global environment.
To explain what caused this mass extinction, scientists have focused on events that would have altered our planet's climate in dramatic, powerful ways. The leading theory is that a huge asteroid or comet slammed into Earth 65 million years ago, blocking sunlight, changing the climate and setting off global wildfires. In recent years, however, researchers have also been investigating whether other forces, including massive volcanic eruptions and changes in sea level, may have contributed to the general environmental decline.
Want to join the conversation?
- Is there any evidence that there were ever any epidemics plaguing dinosaurs? Like the bird flu?(6 votes)
- Yes, the dinosaurs were subject to the plague, but that's not the huge way they go extinct.(5 votes)
- So, did T-Rex go extinct?(0 votes)
- T-rex itself is extinct. There are no more T-rexs living anywhere at all. However, modern birds are closely related to dinosaurs, based on biology, fossil records, and evolutionary studies. That does not mean today's chickens and turkeys are dinosaurs like you would see in Jurassic Park or other dinosaur movies. But it does mean our birds today have dinosaurs in their very ancient family tree, and so sometimes birds are considered "living dinosaurs".(8 votes)
- why does diamond occur in commet and asteroid impact sites? I mean, even in volcanoes they take thousands of years to form(2 votes)
- the asteroids with diamonds might have hit earth thousands or even Millions of years ago(1 vote)
- Could a catastrophic event such as a comet or massive volcanic eruptions not have created an environment for new and novel deseases and viruses to flourish in which creatures including dinosaurs would have had no imunity or defence against not appeared(2 votes)
- what about early humans did they help with the extinction?(1 vote)
- What is the possibility of another mass extinction happening now?(1 vote)
- Many paleontologists believe that essentially, a mass extinction IS happening now, largely due to a combination of human activities including overhunting, land use change/habitat loss, chemical pollution, plastic pollution, and climate change. Whether it will actually reach the catastrophic level of the Big 5 remains to be seen, somewhat depending on our own actions in the next century or see, but it is agreed that species loss is already above general background level that would be expected from natural causes.(1 vote)
- Any tips on how to remember what kinds of creatures died when?(1 vote)
- How did the mass extinction start?(1 vote)
- Could it be a sickness that took out all of the dinosaurs?
like a sickness that can be only caught by them but not mammals because they were warm blooded?(1 vote)
- It is plausible, but not likely a major factor resulting in their extinction. There are many theories that could explain why they went extinct but sickness isn't a really supported theory(1 vote)
- In my opinion i think a lot of disasters happened at the same time volcanoes erupted floods rised meteors crashed earthquakes split the land and eventually killed all the dinosaurs in case you are wondering about the marine dinosaurs there could have been a major drought i hope you agree(0 votes)
- I don't think there was a major drought. Fish survived during the whole extinction, so the marine reptiles could sustain themselves, but marine reptiles like Mosasaurs could only hold their breath for so long. And the air was so smoky, I think that the smoke might have filled their lungs and killed them. But the huge tidal waves during the asteroid impact might have killed some of them too.(2 votes)