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NB: This is not a duplicate of this question, because A) it only asks to wipe out humans, not any other life-form, and B) it insists that one person must survive. The survival of anything is not possible in my scenario, and all of the answers are not applicable to wiping out other animals, plants, fungi and microbes.

This may be a duplicate, but I'm yet to come across a similar question.

Basically, my question is simple; What natural events could wipe out all organisms on Earth, including prokaryotes, in only 15 years, but leave the Earth habitable to microbes at the end of those 15 years?

The 15 year figure can be stretched to up to 35 if it's necessary, and yes, I know it's a really short amount of time. One other requirement is that the disaster must not harm orbital space stations.

That's more or less it, comment if you need any more information.

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    $\begingroup$ I don’t think it’s possible. There are bacteria miles underground with no connection to the Earth’s biosphere, and anything that can wipe them out isn’t going to leave the Earth habitable even to bacteria. universetoday.com/851/bacteria-found-deep-underground $\endgroup$
    – Mike Scott
    Aug 25, 2018 at 19:05
  • $\begingroup$ @MikeScott Oh, I forgot about that. Could those bacteria potentially colonize the surface? $\endgroup$
    – SealBoi
    Aug 25, 2018 at 19:32
  • $\begingroup$ @Sealboi absolutely, given enough time. How long would depend on how different the earth's surface is from their natural habitat after whatever disaster that sterilizes the surface. $\endgroup$
    – Morris The Cat
    Aug 25, 2018 at 19:48
  • $\begingroup$ Possible duplicate of Cleanly remove humanity $\endgroup$
    – dot_Sp0T
    Aug 26, 2018 at 12:50
  • $\begingroup$ Some rogue psychopathic terrorist gains access to a powerful nation's large collection of neutron bombs, decides to go on a little bombing spree across the globe :) $\endgroup$
    – Adi219
    Aug 26, 2018 at 13:30

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Since you clarified that artificial events are also acceptable, I'm going to suggest: self-replicating nanotechnology which is powered by ATP.

ATP is an energy exchange molecule found in essentially all forms of life, and it is a natural one to deliberately make a nano-tech system use. Consider a nano-tech system that deliberately needs its energy as ATP both because we understand it well and because this would in a laboratory environment be an easy way to control its actions or growth.

If the nano-tech then gets out of control, it might spread killing everything on Earth but then would itself run out of energy and fall apart once there is no more ATP to access. There might be some isolated surviving single celled critters but that will be it.

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A massive gamma ray burst (GRB) aimed directly at the earth. The gamma rays would probably not reach the surface in a sufficient dose for mass-extinction but the Nitrogen in the atmosphere would form nitrogen oxides. In combination with water these compunds form a variety of acids, most prominent example would be nitric acid. All higher life on earth would suffocate, and most microbes would die because of the oxidative properties of nitrogen oxides. The seas would essentialy become big acid pools which means that most of the sea life is dead too. Only some extremophiles could survive this but they'd probably survive anything that leaves the earth intact. The nitrogen oxides will begin to decay and after some years (15 should be enough) the earth would be habitable again.

Orbital stations should remain intact struturally but all electronics that are exposed to the radiation will probably suffer. On the other hand the stations and satellites that were on the other side of the Earth than the GRB will stay intact.

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Have a 500 km asteroid hit Earth

Airborne bacteria that arrived after the impact could survive in the atmosphere. The conditions in the atmosphere shortly after impact would make this impossible but given that blackbody radiation is proportional to temperature to the fourth, bacteria can survive at 130C, and that convection currents would keep bacteria up and bring resources to them, it is possible that the upper troposphere/stratosphere is habitable to bacteria.

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    $\begingroup$ No life on this planet can survive magma (at least 600 C) -- your linked article is to a bacteria inhabiting new lava flows - after they have cooled down. There may be a new record-holder, but the highest survivable temp organism. I found was 130 C World’s Hottest Microbe: Loving Life in Hell $\endgroup$
    – Gary Walker
    Aug 25, 2018 at 23:18
  • $\begingroup$ @GaryWalker, You are right, unless xenobiology is allowed. I fixed my answer. $\endgroup$
    – Robert
    Aug 26, 2018 at 11:47
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You need some special mutation that will create an organism able to infect and destroy all living creatures on Earth, including bacteria. Some kind of all-devouring unstoppable virus, changing, adaptable etc.

And then after destroying all life it must die out cause of no "food" or carriers would remain on Earth. Of course it's a very sci fi looking idea, but so is your question. ;)

The Earth will stay habitable, cause all air, water, soil will be fine, moreover it'll be rich with organic remains of previous life. And no poisonous chemicals, radiation, overheating or anything like that.

Of course the plants and power stations will be unattended that might create some problems in future, but I guess that will be in any case - with any natural solution to your task.

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A burst of a zettasievert(*) of radiation would instantly kill any life exposed to it, but it may also detonate any radioactive material on earth, or melt the sky, depending on the type of radiation and what not. Materials that easily turn radioactive might be effected, but bursts of radiation usually do little other than destroy life. Mind you when I say burst, I'm referring to the several millisecond kind, not the couple hour kind.

(A sievert is the dose received in one hour at a distance of 1 cm from a point source of 1 mg of radium in a 0.5 mm thick platinum enclosure. A zettasievert is quite a whole bunch of those! As in, 10^21 of those.)

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    $\begingroup$ Pretty sure that violates the "Must not harm orbital space stations" condition. $\endgroup$
    – Morris The Cat
    Aug 25, 2018 at 19:48
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    $\begingroup$ how can radiation detonate any radioactive material on Earth? $\endgroup$
    – L.Dutch ♦
    Aug 25, 2018 at 19:52
  • $\begingroup$ @L.Dutch Radioactivity amplifies itself, so I figure a strong burst of radiation can spark a rapid decay in certain radioactive materials, but I'm not a nuclear physicist so it's mostly guess work. $\endgroup$
    – Clay Deitas
    Aug 25, 2018 at 20:00
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    $\begingroup$ Amplify itself? If it is so, how come we are still alive after Hiroshima and Nagasaki? $\endgroup$
    – L.Dutch ♦
    Aug 25, 2018 at 20:01
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    $\begingroup$ No, nuclear explosions are not rapid radioactive decay. $\endgroup$
    – L.Dutch ♦
    Aug 26, 2018 at 3:14

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