Wikipedia describes these events: "An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on Earth. Such an event is identified by a sharp change in the diversity and abundance of macroscopic life. It occurs when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life" (Extinction event).
Notice that "macroscopic life" is used as the measuring stick, because "microscopic life" (virus, microbe) is not found easily, if at all, in the fossil record.
Our science tells us that viruses and microbes lived through all of these mass extinctions (Viroids: Survivors from the RNA World?).
However, we are not told what affects the mass extinctions had on them.
Probably because it has not yet been sufficiently considered.
We are only recently discovering much about what the Wikipedia article above mentioned:
"... the majority of diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life ..."(ibid, "Extinction Event"). If you read that closely our science considers extinction events in the context of the few species that are large enough to leave a trail we can follow easily, but does not consider the affects mass extinctions have had on by far the most abundant species: viruses and microbes.
Regular readers know that Dredd Blog has contemplated the impact of mass extinctions on microbes and viruses:
Recently, scientists discovered that even humans and microbes are symbionts, and in fact humans can not reproduce without them.(Are Microbes The Origin of PTSD?). When 50% to 90% of the creatures that microbes and viruses interacted with suffered apocalyptic death, there was no doubt some form of stress.
One can surmise that the K-T boundary extinction event was globally traumatic, since ~90% of land species, including dinosaurs, bit the extinction dust, as did perhaps ~50% of ocean species.
How did the remaining microbes react?
Since the utter destruction and catastrophe caused by the K-T boundary extinction was globally extreme, the microbes that survived would have been extremist types for the most part, otherwise they would have been unable to exist in those new extreme conditions.
The subsequent extreme events of taking over control of mammalian female placenta, establishing a virgin species, or perhaps engendering the adaptability of newts, may have been microbial reactions to the extreme trauma of the K-T boundary extinction event.
The spurious activity caused by any such trauma may explain why not all mammals, for example the rabbit, need those microbes to reproduce.
Evidence, in the form of the oldest rabbit fossil yet found, shows that it originated after the time of the K-T extinction event.
The rabbit, and species close to it, are not like other mammals such as the gorilla, monkey, orangutan, or human, which must have microbe (viral) help in order to reproduce via a functional placenta.
We know that microbial life has flip-flopped from time to time, from pathogen to mutualist, which is in accord with life changing stressful events:
Like pretty much all multi-cellular organisms, humans enjoy the benefits of helpful bacteria. (As you may have heard, there are more bacteria in the human body than cells.) These mutualistic microbes live within the body of a larger organism, and, like any good long-term house guest, help out their hosts, while making a successful life for themselves. It’s a win-win situation for both parties.(Communicating With The Underworld). Humans are the same way, in the sense that they will become cannibals or worse in some stressful situations:
Scientists still don’t understand exactly how these relationships began, however. To find out, a team of researchers from the University of California, Riverside, used protein markers to create a detailed phylogenic tree of life for 405 taxa from the Proteobacteria phylum—a diverse group that includes pathogens such as salmonella as well as both mutualistic and free-living species.
Those analyses revealed that mutualism in Proteobacteria independently evolved between 34 to 39 times, the researchers report in the journal Proceedings of the Royal Society B. The team was a bit surprised to find that this happened so frequently, inferring that evolution apparently views this lifestyle quite favorably.
Their results also show that mutualism most often arises in species that were originally parasites and pathogens.
Uruguayan Air Force Flight 571, also known as the Andes flight disaster and, in South America, as the Miracle of the Andes (El Milagro de los Andes) was a chartered flight carrying 45 people, including a rugby union team, their friends, family and associates, that crashed in the Andes on 13 October 1972. More than a quarter of the passengers died in the crash and several others quickly succumbed to cold and injury. Of the 27 who were alive a few days after the accident, another eight were killed by an avalanche that swept over their shelter in the wreckage. The last 16 survivors were rescued on 23 December 1972, more than two months after the crash.(Wikipedia, emphasis added). Like humans who are intelligent, viruses and microbes also exhibit a form of intelligence (The Intelligence of the Virus realm, The Intelligence of Plants).
The survivors had little food and no source of heat in the harsh conditions at over 3,600 metres (11,800 ft) altitude. Faced with starvation and radio news reports that the search for them had been abandoned, the survivors fed on the dead passengers who had been preserved in the snow.
Some of the microbes have been buried in sediments during these mass extinction events, and are still alive and "doing their thing":
The explanation is that deep life is able to proceed in extreme slow motion. This was illustrated by Price and Sowers (5), who compiled data from a wide range of environments. A typical metabolic rate of microorganisms in ecosystems on the surface of our planet, such as soil, lake water, or seawater, is 0.1 to 10 fmol C⋅cell−1⋅d−1, corresponding to 10−3 to 10−1 g C metabolized per gram cell C per hour (Fig. 1). The mean metabolic rate for deep subsurface bacteria is typically four orders of magnitude lower: 10−5 to 10−3 fmol C⋅cell−1⋅d−1 (6, 7), corresponding to 10−7 to 10−5 g C⋅g−1 cell C⋅h−1. Such numbers are calculated by counting all the microorganisms in a deep sediment core and dividing by the rate at which the main metabolic substrates or products are turning over in the bulk sediment. The process rates are determined from transport-reaction models of pore-water constituents or from direct experimental process measurements using sensitive radiotracer methods. The rationale for taking a mean of the entire microbial community is the assumption that most of the cells are actively engaged in the energy metabolism. This assumption is now strongly supported by the findings of Morono et al. (3).(Deep Subseafloor Microbial Cells on Physiological Standby; cf Carbon & Nitrogen Assimilation in Deep Subseafloor Microbes). They know or detect that something happened to bury them, so, they do what they can to survive ... they wait or adapt ... in very, very slow motion.
Perhaps those of their kind who survived the mass extinctions on the surface "know" that human civilization has now evolved, and that humanity is afraid of them --and humans are therefore making war on them?
Perhaps that human policy will have worse consequences than diplomacy would have (On the Origin of the Genes of Viruses - 11, The Intelligence of the Virus realm, The Intelligence of Plants).
Could it be that there are 40 trillion of the most populous and most experienced living things on this planet yelling "nuke 'em" -- like a few hundred of the tiny population of humans are?
Let's be mutualistic rather than pathogenic.