1. How short was the period of Earth's largest extinction?
In 2014, a study by Burgess and colleagues estimated that the extinction at the end of the Permian period occurred between approximately 251.94 million and 251.88 million years ago. This means the event lasted about 60,000 years [1]. The University of Tokyo also states that the extinction happened within a short period of about 60,000 years [2].
However, this 60,000-year figure has a large margin of error. The research suggests a range from about 12,000 to 108,000 years [1]. Instead of remembering exactly 60,000 years, it is more accurate to think of it as a few tens of thousands to 100,000 years. Even with this uncertainty, the duration is striking. If we shrink the 252 million years since the extinction into one year, the 60,000-year event would last only about 2 hours.
2. How many species died out: 96% or 81%?
For a long time, scientists used the figure that about 96% of marine species went extinct. However, in 2016, researcher Stanley re-evaluated the data and estimated that about 81% of marine species were lost during the end-Permian crisis [3]. The International Union of Geological Sciences (IUGS) page for the Meishan geological heritage site also notes "over 81% (previously about 96%)" regarding the Meishan strata in China [4]. The University of Tokyo press release states that more than 90% of species went extinct [2].
If you look at the survivors, the number of species left went from 4 out of 100 (in the 96% estimate) to 19 out of 100 (in the 81% estimate). This looks like a 4.8 times increase in survivors. However, this is not a case of "96% was wrong and 81% is right." The difference comes from a revision in how the species were counted [3]. Regardless of the percentage, the vast majority of species disappeared. The numbers must be read together with what was being counted.
3. Did Siberian volcanoes cause the extinction, even though they erupted for so long?
A leading theory for the cause is massive volcanic activity in what is now Siberia, located in the northeast of the supercontinent Pangaea [2]. A puzzling aspect is the timing. Burgess and colleagues reported that the extinction happened much more suddenly than the estimated duration of the entire volcanic activity [1]. This suggests the extinction coincided with a specific short phase within the longer period of volcanism. Additionally, a major disturbance in the carbon cycle is thought to have occurred just before the extinction [1].
How did volcanoes affect marine life? A 2021 study by Cui and others focused on carbon dioxide released from volcanoes. Their model estimated that about 36,000 gigatons of carbon were released at a rate of about 5 gigatons per year. This overlapped with the period when magma intruded into rock layers underground. The study concluded this led to warming, ocean acidification, and extinction [5]. Note that these are calculated estimates, not direct measurements. Rising carbon dioxide causes warming, but what specifically harms marine life in hot oceans?
4. Why did hot, low-oxygen oceans make the extinction less severe in the tropics?
In 2018, Penn and colleagues proposed a theory combining ocean warming and oxygen deficiency [6]. As the ocean warms, it holds less oxygen, increasing the metabolic stress on organisms. The study used a "metabolic index" to calculate how much habitable area was lost due to lack of oxygen.
This calculation matched the fossil record. It explained more than half of the extinction severity and also matched the distribution of fossils, which showed that extinction was actually less severe in the tropics [6]. One might expect hotter areas to have worse extinction, but the model showed that the loss of oxygenated habitat was smaller in the tropics, which aligned with the fossils. Two cautions apply: the model explains "more than half," not everything, and while extinction was relatively less severe in the tropics, it was still a major extinction event there.
5. Which animals vanished in the extinction, and why did plant-eaters survive?
The Geological Museum of the National Institute of Advanced Industrial Science and Technology (AIST) notes that trilobites and fusulinids went extinct at the end of the Permian [9]. Both are well-known groups of marine organisms found in fossils. On land, the plant-eating animal Lystrosaurus (a member of the dicynodont group) is found widely in strata after the extinction and is considered one of the few survivors, according to scientific articles [10].
With some groups vanishing and others surviving, how long did Earth take to return to its previous richness?
6. Why did the extinction take 60,000 years but the recovery take about 5 million?
Life did not bounce back immediately after the extinction. Studies estimate the recovery time for oceans and land separately. A study of sediments in Oman, using iron speciation methods, estimated that recovery took about 5 million years. It suggested that the slow recovery was linked to a state where oxygen-rich spots remained scattered in an oxygen-poor, iron-rich ocean [7].
For land, another study estimated that the recovery of terrestrial biodiversity took about 5 million years, based on Triassic vertebrate fossils in Arizona. This is shorter than previous estimates of 15 to 30 million years [8]. However, this was a conference presentation, not a peer-reviewed paper. Although both ocean and land recovery are estimated at about 5 million years, they were studied in different places and on different subjects, so the values cannot be assumed to be identical. Comparing the 60,000-year extinction to the 5 million-year recovery gives a ratio of about 83 times. Given the large error margin in the 60,000-year figure, it is better to think of this as a range of tens to hundreds of times.
7. How can you convert 60,000 and 5 million years into a one-year scale?
If you have a calculator, you can try scaling these times yourself. Let 252 million years equal one year. There are 8,760 hours in a year (365 days × 24 hours). Dividing 8,760 by 4,200 (the ratio of 252 million to 60,000) gives about 2 hours. This is the length of the extinction. On this same scale, 5 million years is about 7 days. Changing the scale helps you see the difference between how fast things broke and how slowly they returned.
You can try a simple observation: put cold water in a clear glass and leave it in the room for about an hour. Small bubbles may form on the inside. This is said to happen because air dissolved in the water comes out as it warms up. This illustrates that "warm water holds less air," which is in the same direction as the explanation for ocean oxygen deficiency. However, this glass experiment does not verify exactly what happened in the ocean during the extinction.
Write down "End-Permian Extinction (about 252 million years ago)," "Volcanic Activity," and "Recovery Estimate (about 5 million years)" on paper and arrange them in order. You can check which numbers come from which studies in the source list. The AIST Geological Museum has a page about the Permian period in Japanese for further reading [9].