SafekipediaExtinction event
Adapted from Wikipedia · Adventurer experience
An extinction event, also known as a mass extinction or biotic crisis, is a time when many kinds of living things quickly disappear from Earth.
During these events, the variety and number of plants, animals, and other organisms drop sharply. Scientists notice these events because species disappear much faster than they normally do.
Scientists think there have been many major mass extinctions in the last 540 million years, but they don't all agree on exactly how many. Some believe there were as few as five big events, while others think there might have been more. These differences happen because it can be hard to decide what counts as a "major" extinction.
These events help us understand how Earth changes and how life can recover after big challenges. Studying them also helps scientists think about how we might protect the variety of life today.
The "Big Five" mass extinction events
In 1982, scientists Jack Sepkoski and David M. Raup looked at how life on Earth has changed over time. They found five big times when many plants and animals disappeared quickly. These events are called the "Big Five" mass extinctions. They happened at different times during a long period called the Phanerozoic Eon.
The "Big Five" happened at the ends of four time periods and one big moment in the middle of a period. They are:
- Late Ordovician mass extinction, 445–444 million years ago
- Late Devonian mass extinction, 372–359 million years ago
- Permian–Triassic extinction event, 252 million years ago
- Triassic–Jurassic extinction event, 201.3 million years ago
- Cretaceous–Paleogene extinction event, 66 million years ago
Each of these events caused many kinds of animals and plants to disappear. For example, the extinction at the end of the Cretaceous period ended the time of the dinosaurs. After each big extinction, new kinds of animals and plants slowly appeared and filled the places left empty.
Sixth mass extinction
Main articles: Holocene extinction and Biodiversity loss
Scientists think we are now in a sixth mass extinction. This is happening because of things people do. Since 1900, animals and plants have been disappearing much faster than usual.
Many species are in danger of disappearing forever. If we do not change our ways, at least 1 million kinds of plants and animals could be lost in the next few years. This is happening faster than it would normally.
Extinctions by severity
Main article: List of extinction events
Scientists study extinction events by looking at changes in Earth’s rocks and the balance of plants and animals. They also look at how many new species appear compared to how many disappear. Early studies often focused on groups of related animals, but later work used smaller groups for more accurate results. Some of the biggest extinctions in history are known as the “Big Five,” and they are highlighted in research papers. These events show how Earth’s biodiversity has changed over millions of years.
| Extinction name | Age (Ma) | Sepkoski (1996) Multiple-interval genera | Bambach (2006) | McGhee et al. (2013) | Stanley (2016) | |
|---|---|---|---|---|---|---|
| Taxonomic loss | Ecological ranking | |||||
| Late Ordovician (Ashgillian / Hirnantian) | 445–444 | ~49% | 57%[d] (40%, 31%)[e] | 52% | 7 | 42–46% |
| Lau event (Ludfordian) | 424 | ~23% | – | 9% | 9 | – |
| Kačák event (Eifelian) | 388~ | ~24%[a] | – | 32% | 9 | – |
| Taghanic event (Givetian) | 384~ | ~30%[a] | 28.5% | 36% | 8 | – |
| Late Devonian/Kellwasser event (Frasnian) | 372 | ~35% | 34.7% | 40% | 4 | 16–20% |
| End-Devonian/Hangenberg event (Famennian) | 359 | ~28%[a] | 31% | 50% | 7 | [f] |
| Serpukhovian | 330–325~ | ~23% | 31% | 39% | 6 | 13–15% |
| Capitanian | 260 | ~47%[b] | 48% | 25% | 5 | 33–35% |
| Permian–Triassic (Changhsingian) | 252 | ~58% | 55.7% | 83% | 1 | 62% |
| Triassic–Jurassic (Rhaetian) | 201 | ~37%[c] | 47%[c] | 73% | 3 | N/A[g] |
| Pliensbachian-Toarcian | 186–178 | ~14% | 25%, 20%[e] | – | – | – |
| End-Jurassic (Tithonian) | 145 | ~18% | 20% | – | – | – |
| Cenomanian-Turonian | 94 | ~15% | 25% | – | – | – |
| Cretaceous–Paleogene (Maastrichtian) | 66 | ~39% | 40–47% | 40% | 2 | 38–40% |
| Eocene–Oligocene | 34 | ~11% | 15.6% | – | – | – |
The study of major extinction events
Breakthrough studies in the 1980s–1990s
For much of the 20th century, it was hard to study big die-outs of life because there wasn’t enough information. Scientists thought these events were just rare exceptions to slow, gradual changes in life on Earth. This changed in 1980 when a team led by Luis Alvarez found evidence of an asteroid impact at the end of the Cretaceous period. Their Alvarez hypothesis for the end-Cretaceous extinction brought new attention to the idea that sudden, catastrophic events could cause big die-outs.
Another important study came in 1982 when David M. Raup and Jack Sepkoski showed five major times when many sea animals died out. These times were at the ends of the Ashgillian, Late Permian, Norian, and Maastrichtian periods, and also during the Devonian period. Their work helped scientists see that big die-outs are important parts of Earth’s history.
New data on genera: Sepkoski's compendium
After Sepkoski died in 1999, his collection of data about sea animals was published in 2002. This led to many new studies about how big die-outs affected life on Earth. Scientists used this data to see how new species appeared at the same time as die-outs. Some found that big die-outs happened quickly, which greatly changed biodiversity. Others studied how different groups of animals were affected by these events.
Tackling biases in the fossil record
As more information became available, scientists realized that the fossil record didn’t always show the real timing or how bad the die-outs were. For example, the last fossil of a species might appear before a die-out, but the species could have died out because of that event. This is called the Signor-Lipps effect. To deal with such challenges, scientists created new ways to estimate how many different types of animals there were more accurately. These ways help fix problems like missing fossils or uneven checking over time.
Uncertainty in the Proterozoic and earlier eons
Because most life on Earth was made of tiny microbial organisms, it is hard to find evidence of early extinction events in fossils. Most known extinction events happened during a time called the Phanerozoic eon, when animals with bones and shells lived. One exception is the Oxygen Catastrophe that happened around 2.45 billion years ago during the Proterozoic eon.
Scientists think the background rate of extinctions — how often species naturally disappear — is about two to five groups of ocean animals every million years, based on what we can see in the fossil record. The Oxygen Catastrophe may have been the first big extinction, but because we know so little about life from that time, it is hard to compare it with later extinctions.
Evolutionary importance
See also: Evolutionary radiation and Macroevolution
Mass extinctions have sometimes helped new types of life on Earth to grow. When one group of animals disappears, another group can take its place. This is not because the new group is better, but because the old group is gone.
For example, mammaliaformes and then mammals lived when the dinosaurs were around, but they could not take over because the dinosaurs were too strong. The end-Cretaceous mass extinction removed the dinosaurs, which allowed mammals to grow and take over. The dinosaurs themselves had grown because of an earlier mass extinction, the end-Triassic, which removed their rivals, the crurotarsans.
Patterns in frequency
Some scientists think that extinction events happen in a repeating pattern, roughly every 26 to 30 million years. They have ideas about why this might happen, like the influence of space objects or movements in our solar system. Other scientists believe there isn’t strong evidence for these patterns.
Mass extinctions often happen when a long-term problem is made worse by a sudden event. Over time, some groups of animals have become better at surviving because of changes in their food chains and other factors. The rate at which new species appear and old ones disappear has slowly gone down over the past 500 million years.
Causes
Scientists are still trying to understand why mass extinctions happen. Sometimes, when nature is already stressed, a sudden shock can cause many plants and animals to die out.
The most common ideas about why mass extinctions happen include big volcanic eruptions, changes in sea levels, asteroid impacts, and big changes in climate. Flood basalt eruptions could have made dust and smoke that blocked sunlight, hurt acid rain could have damaged forests, and carbon dioxide could have caused long-term global warming. When sea levels drop, it can hurt sea life and change weather patterns. Asteroid impacts could have caused big problems for food chains by blocking sunlight.
Other factors like global cooling, low oxygen in the oceans, and hydrogen sulfide emissions can also stress nature in different ways. Today, human actions like climate change and losing habitats are also causing worries that we might be causing a new mass extinction.
Effects and recovery
The effects of big die-outs changed Earth in many ways. After a big die-out, only tough plants and animals survive. These are animals that can live almost anywhere. Later, new animals and plants grow and fill the empty spaces. It usually takes millions of years for life to grow back to what it was before.
The biggest die-out happened long ago, during the Permian–Triassic extinction. It hurt most of the life on Earth. Life seemed to grow back quickly, but it was mostly just a few tough animals, like Lystrosaurus. Scientists now think it took much longer for the world to fill with many different animals and plants again. This slow growth may have been because the Earth kept having problems for many years.
In media
The term extinction-level event (ELE) has been used in many stories. For example, the 1998 film Deep Impact shows what could happen if a comet hit Earth. The film calls this an ELE.
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