How could life develop on a planet with 9-year days

Question

In some of my first questions on this site I asked about a world with a day that lasts 9 years. Many people agreed that life on this planet could survive via migration, but not evolve. The problem lies in the earliest stages of evolution, as microscopic single-celled organisms would not know to or be able to migrate. The earliest creatures would die after only being around for 4.5 years until they entered the night and froze to death. I pride myself at explaining everything realistically, but I have failed to explain how life could evolve in a world like this.

Assuming every detail other than its day length is the same as Earth, how could complex life evolve?

Answer 1

The idea of volcanic vents to harbor life during the long night that others have suggested is really good. But that won't help during the long day if it gets to hot and dry.

One variable that would help is the planets orbit. If the planet had an orbit on the outer edge of the Goldilocks Zone so that daytime temperatures stay at a reasonable level, with an average daytime temperature of 18 C (65 F).

If it also has lots of high glaciers that would build up over the long winter, and then slowly melt over the summer to keep things wet, and you'd also get some good storms near the terminators.

Plant life would wake up around dawn as the ice melted and the dawn storms began, starting on the plains, and then along the river valleys during mid morning, as the snow continued to retreat.
Things would begin to dry out around noon, with plants on the plains dropping seed and drying out, and plants along the glacial melt rivers taking off. By later afternoon when the storms started up again life on the plains would resurge.
As dusk approached, the plants on the plains would die off, dropping their seeds again, and trees and other large plants would begin to harden for the long cold.
As night falls, plant life would be limited to species that don't depend on photosynthesis, huddled in isolated areas around geothermal vents and volcanic activity.

Animal life would be mainly migratory, with different species sticking to different bands of the day. There would be some that live their entire lives in the cold of early morning. Others would constantly travel the lush prairies of early afternoon. The valleys and river areas would be havens for animals during the warm afternoon, and birds would build nests, raise their young, and then move on to new nests as the day progressed. Others would live on the midday plains, drinking the dew, and feasting on the seeds dropped during late morning.
The zones then reverse as dusk approaches and the rains start, with large herds traveling the plains, and then the cold weather animals as the sun sets.

Predators would travel along with their preferred prey, only occasionally moving out of their area of the day.

Large cities probably wouldn't develop, unless the planet was tilted in such a way that something more stable could exist near the pole. Otherwise they would be highly nomadic, following the herds or moving along from river to river. Different tribes would most likely stick to specific parts of the day, though there may be some that would travel between zones.

And then there was the legend of the family that was fleeing from raiders far into night, and took refuge in an area with a lot of volcanic activity, living on mushrooms and other nocturnal plants until dawn.

Answer 2

The solution is actually pretty simple, antifreeze and hibernation.

There are already plenty of bacteria that can survive being frozen and then recover. Many plants have a life cycle where they grow during summer and then scatter seeds that last through winter. What you are describing here just needs an extension of this and life would have evolved to keep with it.

The very early stages of life obviously won't have that developed, but that doesn't need to be a problem. Freezing is only harmful to cellular life because the ice crystals that form rupture the cell walls. Life on this planet though would evolve something to survive that. Either internal antifreeze, or elastic cell membranes, or something completely different.

Something else to consider is that one of the likely initial locations for life to have formed is volcanic pools and they would remain defrosted even through the long night. As life develops and moves away from these locations it would have time to develop the survival mechanisms it needs.

Answer 3

Life in the sea would have a far easier time than life on land. Oceans are huge and have an enormous thermal inertia. So the sea surface might freeze over globally, but the ocean depths would still be liquid.

Perhaps even the land life could survive by returning to the oceans for the 4.5 year night? Some kind of marine tadpole turns into a frog and lives on land during the day, then reverts back to a tadpole and lives in the sea at night.

You might want to check out stuff about Snowball Earth prehistoric Snowball Earth for how life survived then, though obviously Earth still had sunlight, so your creatures may have to have survived on chemosynthesis not photosynthesis. theories on life surviving

Answer 4

Depending on the axial tilt of your planet, the poles might be an option. At near 0° tilt, the poles could easily be warmer than the night-side equator.

With 0° tilt, someone standing at either pole would always be in sunlight (as slight as it may be); taller objects are more likely to get sunlight at their tops. Closer to the star (or larger star), this would apply further from the poles (if only slightly). This would give the poles a far more consistent thermal profile than the equator (with it's rather long periods in sunlight and darkness).

Answer 5

There's no real reason that a long day-night cycle would make it difficult for life to exist or evolve. Consider: there are animals that live in deep caves and deep oceans for whom there is no day-night cycle of any kind.

But even for regular surface-dwelling life the major issue (to my mind) would be related to temperature. This could be a problem with things like frigid temperatures at night and reliable water sources evaporating during the day or baking soil. These have a lot of ordinary meteorological solutions-- I've experienced plenty of warm nights and cool days, and it's always possible that life can only develop in a narrow climatic region of your planet (even if life forms migrate elsewhere later on).

You could also have an atmosphere conducive to heavy cloud cover, mitigating the sunlight substantially, as long as there is enough gravity/atmosphere/ozone (or equivalents) to keep water from escaping into space. Or there could be geographic regions that provide for a reliable amount of shade during the long days, like a fortuitously positioned valley among mountains such that there is always significant shade cover. And water itself could be stored in huge, deep oceans large enough to withstand evaporation processes during the day or in underground aquifers (where even if the temperature were high enough to evaporate the water it would quickly condense again).

Answer 6

2 comments:

1. One theory proposes that life on Earth originated in deep-sea hydrothermal vents (see here: http://www.space.com/19439-origin-life-earth-hydrothermal-vents.html). This type of life takes advantage of chemical gradients created by volcanism, and does not care much about the Sun. So, if your planet has an ocean, then the length of the day would not matter in terms of the origin of this type of life. (One can imagine this type of life existing almost anywhere; see here: https://aeon.co/essays/could-we-make-our-home-on-a-rogue-planet-without-a-sun).

2. A planet that spins that slowly is basically tidally-locked for practical purposes. One possible state of a planet like this is an "Eyeball" world, where the part of the planet that faces the star gets the lion's share of the stellar energy and has different properties than the rest of the planet. One flavor of Eyeball planet is an ice-covered world that has a large thawed pond where it receives the most energy from the star (see here: http://nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets).

The more Earth-like possibility is the "hot Eyeball planet", which is very hot on the sunlit side and cold on the night side. The night side has ice caps that slowly melt and provide a trickle of water. The best place for life is in a narrow ring around the planet at the terminator (where the Sun is always near the horizon). See here for more details: https://planetplanet.net/2014/10/07/real-life-sci-fi-world-2-the-hot-eyeball-planet/

If the planet was rotating slowly enough, then I don't think the basic "Eyeball" picture would not change too much, but would simply be slowly shifting as the planet spun.

Answer 7

Think about what the weather would be like along the day/night boundary. The daylight side of the boundary would have hot air heated by the sun, rising. Cold moist air from the night side would flow across the boundary to replace the hot rising air. So you would have strong winds (and possibly ocean currents) moving continuously from the dark to the light. Microscopic critters would get a free ride out of the darkness into the light.

Answer 8

I agree with some of the other answers, but I would like to add:

In such a slow day/night cycle, it would be possible, once life gains mobility, to live comfortably in the dawn/dusk area, slowly migrating away from Noon and staying in the comfort zone. These life forms would essentially be eternal nomads, constantly traipsing north and south along the break of day or sunset.

If intelligent life arrives or evolves here, they could conceivably have roaming city-states, moving when the day gets too hot, setting up camp when they reach winter, planting crops in the spring, etc. Provided there was land or narrow seas that they could continually use to traverse the planet - it would be an immense shame if they ended up cornered with nowhere to go as Noon or Midnight approach.

Answer 9

As I discussed in my answer to one of your previous questions life on this planet is going to be very difficult for highly evolved life, let alone simple, recently emerged life. So why not have life develop under different circumstances?

One thing I mentioned is that in order for the day side to not be an oven, the planet needs to get less sunlight than Earth does. This can happen with either the star being less bright than ours, or by being father away.

So consider this - the planet starts out much more like Earth, but with a fairly elliptical orbit. To get to its current more distant orbit, millions of years ago a rogue planet came through the solar system. The rogue planet passed by your planet while it was at the farthest point its orbit and threw your planet into a circular orbit and slowed its rotation.

I'm not sure what exactly it would take to make this work in terms of how big the rogue planet would have to be, how close it would have to pass, and how much it really could affect your planet's orbit. However, the inhabitants of your planet aren't really going to be able to know those things either - I believe that they would be able to figure out that the planet used to have a different orbit and day length, and that some catastrophic event changed that, but they won't know what the old orbit was and the rogue planet will be long gone.

In short, there was an extinction-level event millions of years ago that changed the conditions the planet to what they are now.

Answer 10

It's possible the ocean wouldn't freeze during the long night but there's a better approach:

Life based around volcanic vents. They don't have to worry about the long night. Now, the deep-ocean vents will have no chance of evolving more ordinary life forms.

However, consider what happens when that volcano reaches the surface. Now they are also exposed to sunlight and photosynthesis could develop. Any given volcano will have very little chance of causing this step but eventually it might happen because a dual-powered organism would have a competitive advantage.

Now the dual-power organisms have a chance of developing some way of surviving the dark.

Answer 11

The problem lies in the earliest stages of the evolution, as microscopic single celled organisms would not know to or be able to migrate.

The problem is not related to "knowing" to migrate. Plants grow toward the sun but don't have any "knowing" of what the sun is. Your one-celled life could simply move towards the energy.

The only problem is the ability to move towards the sun. As others have suggested, this can be overcome either with an alternative heat source or with the "life" being so simple as to be able to survive a long cold period and reanimate when conditions allow. Eventually life would evolve the ability to follow the energy (sun).

Answer 12

Just because the advanced life lives with 9 year days, doesn't mean that the planet has always had 9 year days, perhaps over billions of years the planet has been progressing towards some sort of tidal locking with its parent star? The most stable stars in our universe tend to be small, with planets nearby being the habitable ones, these in turn are more susceptible to tidal locking, which once it had occurred would lead to the development of an eyeball type planet (see other answer!)

Answer 13

The way I see it you don't have to explain it. Evolution is a chain of mutations and random behaviours that work out well. Say we have a frog like thing. Either one frog would accidentally start migrating and then breed a whole line of migrating frogs or it would be lucky enough to have a built in anti-freeze type deal for night, which it would then pass on.

From a writing perspective, don't even bother explaining it. Look at Star Wars, why would wookies evolve to have massive furry bodies when the live on a tropical planet that has a very warm climate. it doesn't have to make sense as long as its cool and interesting.

Answer 14

With how slowly the planet rotates, it would evolve to be nomadic, moving slowly across the twilight zone. I'm thinking that with vegetation, it would evolve to be resistant to both extreme heat and drought, and extreme cold and darkness. I'm thinking that it would remain in torpor until twilight comes, or plants will scatter their spores towards the twilight zone, where they lie in wait until conditions become suitable.