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Course: Biology library > Unit 26
Lesson 1: Evidence of evolution- 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
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A brief history of mass extinctions
Species go extinct all the time. Scientists estimate that at least percent of all species of plants and animals that have ever lived are now extinct. So the demise of dinosaurs like T. rex and Triceratops some million years ago wouldn't be especially noteworthy—except for the fact that around percent of all life alive at the time also died out, in what scientists call a mass extinction.
Mass extinctions—when at least 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 million years ago, when perhaps percent of all species went extinct.
Five mass extinctions
Ordovician-Silurian Extinction: Small marine organisms died out. ( mya)
Devonian Extinction: Many tropical marine species went extinct. ( mya)
Permian-Triassic Extinction: The largest mass extinction event in Earth's history affected a range of species, including many vertebrates. ( mya)
Triassic-Jurassic Extinction: The extinction of other vertebrate species on land allowed dinosaurs to flourish. ( mya)
Cretaceous-Paleogene Extinction: ( mya)
million years ago: a mass extinction
Scientists refer to the major extinction that wiped out non-avian dinosaurs as the K-Pg event (formerly called the K-T extinction) because it happened at the end of the Cretaceous Period and the beginning of the Paleogene. Why not C-Pg? Geologists use "K" as a shorthand for Cretaceous based on the German word “kreide”, for which the Cretaceous Period with its chalky sediments is named.
The K-Pg 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 Paleogene period.
We can see the impact of this event in the fossil record. Fossils that are abundant in earlier rock layers are simply not present in later rock layers, after the event. A wide range of animals and plants suddenly died out, from tiny marine organisms to large dinosaurs.
Changes in the environment
What happened to cause such widespread devastation 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 slammed into Earth million years ago, blocking sunlight, changing the climate and setting off global wildfires. In recent years, researchers have also been investigating whether other forces, including massive volcanic eruptions and changes in sea level, may have contributed to the environmental changes.
Want to join the conversation?
- Is there any evidence that there were ever any epidemics plaguing dinosaurs? Like the bird flu?(7 votes)
- Yes, the dinosaurs were subject to the plague, but that's not the huge way they go extinct.(5 votes)
- If the sunlight was blocked how the plants survived ?(3 votes)
- Well first, sunlight wasn’t completely blocked out and prevented from reaching the Earth’s surface. The amount reaching the surface was greatly diminished, but still some sunlight made it through.
Second, not all plants have the same demands. Some plant species adapted to life with limited sunlight. Some plant species surely died off, but the ones which evolved to be more hardy survived.(5 votes)
- Any tips on how to remember what kinds of creatures died when?(3 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".(9 votes)
- How did the mass extinction start?(2 votes)
- by an asteroid(2 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)
- Why did the asteroid killed the dinosaurs?(1 vote)
- Because he's mean. A better-sounding reason is that its path and other gravitational forces acting on it made it collide with the Earth.(3 votes)
- What happened to cause such widespread devastation 65 million years ago?(2 votes)
- 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)