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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.

SealBoi
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    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. https://www.universetoday.com/851/bacteria-found-deep-underground/ – Mike Scott Aug 25 '18 at 19:05
  • @MikeScott Oh, I forgot about that. Could those bacteria potentially colonize the surface? – SealBoi Aug 25 '18 at 19:32
  • @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. – Morris The Cat Aug 25 '18 at 19:48
  • Possible duplicate of Cleanly remove humanity – dot_Sp0T Aug 26 '18 at 12:50
  • 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 :) – Adi219 Aug 26 '18 at 13:30
  • You say natural events. Are artificial accidents acceptable? – JoshuaZ Aug 27 '18 at 03:08
  • @JoshuaZ sure, I guess I thought that something artificial wouldn't be as powerful as a natural event. – SealBoi Aug 27 '18 at 08:27
  • @Adi219 All the neutron bombs we have or could feasibly build wouldn’t come close to sterilising the Earth. People have a highly exaggerated view of the power of nuclear weapons, which are big and destructive on a human scale but very small indeed on a planetary scale. – Mike Scott Aug 27 '18 at 18:00

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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.

MichaelK
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JoshuaZ
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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.

CKA
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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.

Robert
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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.

Uk rain troll
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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.)

Clay Deitas
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    Pretty sure that violates the "Must not harm orbital space stations" condition. – Morris The Cat Aug 25 '18 at 19:48
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    how can radiation detonate any radioactive material on Earth? – L.Dutch Aug 25 '18 at 19:52
  • @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. – Clay Deitas Aug 25 '18 at 20:00
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    Amplify itself? If it is so, how come we are still alive after Hiroshima and Nagasaki? – L.Dutch Aug 25 '18 at 20:01
  • I think you’ll find that two miles of rock are a pretty effective radiation shield, and so are four miles of water. You won’t get all of the bacteria. – Mike Scott Aug 25 '18 at 20:13
  • @L.Dutch Aren't nuclear explosions just rapid decay of radioactive materials caused by a chain reaction? Like that. Ampliyfy, triggers, self decays. Whichever. – Clay Deitas Aug 25 '18 at 20:41
  • @Mike Scott I knew water had radiation blocking properties, but I didn't realize how well they blocked things like gamma rays. I ended up doing the calculations and it would take 12,000 orders of magnitude more energy to kill all life on earth than is produced by he average Gamma Ray Burst. – Clay Deitas Aug 25 '18 at 20:45
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    No, nuclear explosions are not rapid radioactive decay. – L.Dutch Aug 26 '18 at 03:14
  • @L.Dutch Sorry, I don't have any nuclear weapons so the lie they tell us civilians is all I know. – Clay Deitas Aug 26 '18 at 04:07
  • Clay, you can find a reasonably accurate if non-quantitative explanation of nuclear explosives in most textbooks for general education physical science (that is the course that, say, art majors in US colleges take to cover their science requirement). And you can find more detailed explanations in other openly available source. In the web era the problem you have informing yourself is rarely a lack of information, but rather the flood of deliberate and unintended mis-information. I would categorize this post as the latter. – dmckee --- ex-moderator kitten Aug 26 '18 at 18:50
  • @dmckee Are you referring to my take on nuclear exsplosions, or some other part of my post? – Clay Deitas Aug 26 '18 at 19:38