The information presented in the previous episode is out of date.

In an alternate universe, there is still an Earth in geochemistry only. This one, Alternate Earth 600, is a "backwards Earth". Instead of 24 hours, a day lasts 42 hours. Instead of 12 months, a year lasts 21 months (translated into roughly three Terran years.) Instead of orbiting one sun, it orbits two (a G-type binary). Instead of rising from east to west, the two suns rise from west to east. Which means that instead of 22.1 to 24.5 degrees, its axial tilt alternates from 112.1 to 114.5 degrees. It bears some resemblance to Chris Wayans's "Serrana":

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The deepest ocean trench is 3.2 miles. The tallest peak, on the other hand, is 5.7 miles above sea level. What look in the picture like tiny little rivers are actually flooded faults (similar to Malawi, Tanganyika and Victoria) that are processing to break up this supercontinent.

Today, this alternate Earth has no multicellular lifeforms--all you'll ever find there are marine microbes. The atmosphere is identical to the Cambrian of back home--levels of carbon dioxide are 4500 parts per million, yet oxygen still makes up 12.5% of the atmosphere.

To that end, one of our scientists, who was uninterested in single-celled germs, decided to terraform that planet, which is against the law according to the scientific community. Unlike Serina, in which the list of seeds is short, vague and seemingly random, his seedlist is a long one, consisting of most (not all) of the algae, plants, fungi and animals that we humans have used for human purposes--food, pets, show, research, pest control, pollination, to name a few. (If you want the whole list, let me know in the comments below.)

However, would any of the seeds, who evolved to work on a planet of 24-hour days and 365-day years, survive the initial try in their new home with astronomical differences, or would there be an instant mass extinction?

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    $\begingroup$ Ummm, you seem to have missed a critical data point. What is the temperature of this planet? Seems to me, the seasons are all out of whack. How can we determine the 'growing season', and the temerature ranges, necessary to determine the viability of various plant species? $\endgroup$ Sep 11, 2020 at 0:57
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    $\begingroup$ The other very important atmospheric gas is nitrogen. There are very few earth species that will survive without nitrogen in the atmosphere. In fact without nitrogen, life as we know it on earth is impossible. $\endgroup$ Sep 11, 2020 at 1:00
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    $\begingroup$ 1) Lots of plants and animals survive above the arctic circle, where days last a lot longer than 42 hours. 2) You can't have a sun rising in the west, since east and west are DEFINED by the direction of rotation. $\endgroup$
    – jamesqf
    Sep 11, 2020 at 3:49
  • $\begingroup$ @jamesqf Tell that to Venus. $\endgroup$ Sep 11, 2020 at 10:07
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    $\begingroup$ @JohnWDailey Because it's a completely different planet in a completely different star system? It's like saying an ostrich is an alternate kind of dog. $\endgroup$
    – rek
    Sep 14, 2020 at 15:45

1 Answer 1


For plants that evolved on a 24 hour light cycle planet, some do surprisingly well at other cycle lengths. Cycles of up to 38 hours are used in indoor hydroponic setups. You can take the work of indoor hydroponic enthusiasts and use it as a starting point.

This link talks about optimum day length vs optimum night length for various plants:

  • Short day plants: These require a long period of darkness to photosynthesize and produce flowers. If they are exposed to over 12 hours of light per day, they will not flower. Poinsettias, strawberries, cauliflower, and chrysanthemums are short-day plants. These cant grow outdoors on your planet generally.

  • Long day plants: These require up to 18 hours of sunlight per day. They include wheat, lettuce, potatoes, spinach, and turnips. These will grow at some spots on your planet seasonally.

  • Day-neutral plants: These are the most flexible. They produce fruit no matter how much light they are exposed to. Some examples include rice, eggplant, roses, and corn. These will grow on your planet.

Some highly motivated people have calculated the optimal day length (NSFW) for different stages of plant growth (well, one valuable plant in particular). 32 hour days for seedlings (24 light, 8 dark), 24 hour days while flowering (12:12).

My local friendly neighbourhood hydroponics store sells light timers which support cycle intervals up to 99 hours.

Your planet will support plant life. Not all plants, and not everywhere, and crop yields will be all over the place. But they'll grow. Life is surprisingly resilient and adaptable.

  • $\begingroup$ This raises a couple more questions. One--do you know where I can find a comprehensive list of all the long-day and day-neutral plants that we have used in our gardens and crops? Two--anything on the algae, fungi and animals? $\endgroup$ Sep 11, 2020 at 1:50
  • $\begingroup$ I dont know of a definitive list. Just what I got from the hydroponic pages. I dont know and couldn't find anything with googling. But I do know Life is surprisingly resilient and adaptable. I suspect it will survive. $\endgroup$
    – Ash
    Sep 11, 2020 at 1:56

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