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So as the title describes, I need an apocalyptic event which is survivable by cryogenically preserved humans in hermetically sealed bunkers underground (or somewhere else). This event should wipe out almost all life and change the climate and environment sufficiently enough that life with completely different biochemistries can evolve.

Possible ideas:

  • Close (20 ly) gamma-ray burst: Superheating and ionization of the atmosphere. This wouldn't really cause a complete redesigning of life as we know it. Although new species will arise, they will likely have the same or similar biochemistry as current life.

  • Asteroid impact: Again, it wouldn't change biochemistry much.

  • Nuclear winter: The same problem.

Any ideas?

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    $\begingroup$ Biochemistry is pretty basic and hitting the reset button is not only very drastic but would set life back not just millions but possibly billions of years. What do you mean by biochemistry? $\endgroup$ – Lee Leon Jan 17 '18 at 9:15
  • $\begingroup$ There is only one 'biochemistry' on Earth. If you want a new biochemistry, you are going to have to erase all life and start over. The bacteria in our bodies are so developed that they would have a huge competitive advantage over any newly evolved life forms. It is not reasonable to have a new biochemistry while keeping humans intact. $\endgroup$ – kingledion Jan 17 '18 at 17:06
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This event should wipe out almost all life and change the climate and environment sufficiently enough that life with completely different biochemistries can evolve

It's going to need a lot of handwaving, but you can have a comet "strike" (actually, burn and partially dissolve in the upper atmosphere) Earth.

The comet is mostly made up of dirty water ice, and the "dirt" is actually a sludge of space-evolved bacteria and viruses. If these bacteria are not based on the same exact DNA code as Earth life, and yet have evolved to be able to optionally prey on Earth proteins, there would be very little defense against infection, and the bacteria would wreck the biosphere. At the same time, the viruses could trigger all sort of mutations in surviving organisms, including mutations giving increased resistance to infection.

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  • $\begingroup$ I was going to answer the same way; a comet strike that introduces new bacteria/viruses that actually change the environment. But the problem is that when your characters wake up from their hibernation they wont have defenses against it either. Unless that's what your story calls for. $\endgroup$ – Len Jan 17 '18 at 17:23
  • $\begingroup$ Maybe humans are immune to it because of excellent medical technology (OP doesn't specify a timeframe, so it could be well into the future), but wildlife has no such protection. $\endgroup$ – Ave Roma May 19 '18 at 1:30
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1: Invasive species from elsewhere.

war of the worlds landscape http://waroftheworlds.wikia.com/wiki/Red_weed

If you want an ecosystem to turn into a radically different ecosystem at some rate faster than ordinary geological/evolutionary time, have the radically different ecosystem move in and displace what was there. That happens on Earth not infrequently.

Have organisms with your desired biochemistry show up from elsewhere. There are many possible sources - space, alternate dimension, alternate timeline, Earth's future or past, experimental lab creations etc. Bonus: make them as you like. These things proceed to systemically displace the organisms of Earth, and you can have this occur right down to the level you desire. Maybe only Archons survive in their inhospitable refugia. Or maybe them too. Your invaders can adapt, more or less.


2: Clear off the earth of earth beings with help from Outside.

cthulhurising the earth https://torontoist.com/wp-content/uploads/2016/11/Cthulhurising-640x360.jpg

from the diary of Wilbur Whateley, The Dunwich Horror

Grandfather kept me saying the Dho formula last night, and I think I saw the inner city at the 2 magnetic poles. I shall go to those poles when the earth is cleared off if I can’t break through with the Dho-Hna formula when I commit it. They from the air told me at Sabbat that it will be years before I can clear off the earth, and I guess grandfather will be dead then, so I shall have to learn all the angles of the planes and all the formulas between the Yr and the Nhhngr. They from outside will help, but they cannot take body without human blood. That upstairs looks it will have the right cast. I can see it a little when I make the Voorish sign or blow the powder of Ibn Ghazi at it, and it is near like them at May-Eve on the Hill. The other face may wear off some. I wonder how I shall look when the earth is cleared and there are no earth beings on it. He that came with the Aklo Sabaoth said I may be transfigured, there being much of outside to work on.”

Similar to #1 except the things which wish to clear off the Earth were the entities who owned the earth long before and then were somehow displaced. They want it back, and the way it was. I think only the loosest sense of "biochemistry" would describe these things which want to repossess the Earth. In this context, all extant biological life are "earth beings".

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Biochemistry of the life as we know it is entirely based on the chemistry, that is available elements, of the planet we live on.

Wiping out life will likely set up again the same biochemistry if you leave the available elements unchanged.

Unfortunately, changing the chemistry of an entire planet while preserving a tiny bunker hosting some cryogenically stored humans is hardly possible. I.e. wiping out phosphorus and set up an arsenic based biochemistry would require something like building the planet from scratch.

Probably your safest bet is to have that the new life starts with different chirality:

The origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's "choice" of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality.

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  • $\begingroup$ @RealSubtle, I agree with you, but OP doesn't ask to move on another planet. $\endgroup$ – L.Dutch - Reinstate Monica Jan 17 '18 at 9:04
  • $\begingroup$ @RealSubtle, just delete it from here and repost it where it should go $\endgroup$ – L.Dutch - Reinstate Monica Jan 17 '18 at 15:27
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To create a complete new biochemistry, we are going to make carbon-carbon bonds obsolete. Carbon-carbon bonds are the backbone of our carbon-based life. To make them obsolete, we will force life to resort to some other basic bonds.

Radiation in the wavelength of 330-350 nm will be absorbed by carbon-carbon bonds, and if enough energy is provided, it will break the bond. If I am not completely off, Si-Si bonds absorb chiefly in the range around 460nm.

Nitrogen-gas lasers spark in the 340nm range, which is exactly what we would need. Now, on Earth there is a lot of C-C bonds, so the energy needed to succeed will have to be rather large, and the dosage will need to occur over a longer period of time.

To achieve this, we are going to add a new satellite to the Earth. This new celestial body is heavy and covered in a sufficiently dense atmosphere of nitrogen. The body itself is made of piezoelectric material and, not being tidally locked to the Earth, it suffers constant tidal forces, which translate in huge sparks across the nitrogen atmosphere, resulting in a constant, Moon-size, UV laser pointed at the Earth.

The new satellite, Moon2, also carries a smaller set of its own satellites, all made of solid CFC. When Moon2 is captured by the Earth, its satellites fall onto our planet, burning in the atmosphere and releasing massive doses of gaseous CFC, which get rid of the ozone layer, and make our Nitrogen laser way more effective.

Let Moon2 in orbit long enough, and carbon-based life may become less-likely than silicon-based life. The massive doses of CFC may also poison the larger life-forms, which stood a better chance of surviving the radiation, or actively find shelter.

Some pockets of carbon-based life may remain, hid in caves, or deep at the bottom of the seas, but as time passes, they will become just niche-survivors, as rare as a Dodo today.

Finally, let the Moon and Moon2 collide together before waking up the humans, and welcome them back with a huge firework.

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