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How would life on Earth have evolved and look like if our planet was orbiting a brighter and hotter Sun?


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#1
CyberMisterBeauty

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I'd like to write a story or make an animation showing how could life in a habitable Earth-like planet would evolve if it was orbiting a F main sequence star. They are hotter and brighter than the Sun but they also live less time in the main sequence phase. These stars live around 3-8 billion in this phase which could make life evolve in somehow in such a planet.

 

So I think for a F main sequence star it have to be a F9V, F8V or at most a F7V spectral type to give the chance of large and complex multicellular life to evolve in an orbiting Earth-like planet.

 

For exemple I think that the star 19 Draconis is a good exemple. It is a F8V spectral type, have twice the luminosity of the Sun and has a surface temperature of almost 6300k and it have practically the same age as the Sun.

 

I read in an article that F main sequence stars release far more UV radiation than G main sequence stars( the hotter the star more UV and Xrays it emits) and it is written in the article that these higher ultraviolet levels could be both an advantage and a drawback at the same time for the development of life.

 

Higher UV levels hamper the development of DNA molecules since it destroys and deforms its structure more easily which means that it could hamper and even disrupt the development of complex life beyond microbial life. The article says that F stars release 2 to 7 higher UV levels than the Sun.

 

However higher UV levels could be a good thing and it could actually trigger the development if life faster and more efficient than a star like the Sun. Since F main sequence stars release more blue light than the Sun since they are hotter it could trigger more photosynthesis in both shallow and deeper levels in the oceans. Blue light have shorter wavelenghts than the other colors of the spectrum including red and since small molecules like water absorbs and scatter blue most efficiently than the other colors and blue/violet light is the shortest wavelenght it could reach deeper deaths of the oceans allowing more photosynthesis to happen there than here on Earth. Algae and bacteria in the ocean would exist in much higher number with more species and therefore the sea could even have another color rather than blue due to the greater variation and higher number of species of algae. Since also blue and ultraviolet light have more energy and F stars release more of it it could act as a stronger incentive to do more photosynthesis in a more efficient way. And since water is a very good UV protector it would not hamper the development of complex life.

 

As a consequence the oxygen levels of the atmosphere of my hypothetical planet orbiting the F main sequence stars would reach the optimal 20% levels much earlier than it happened here on Earth. The ozone layer would have formed much earlier too.

 

Now the most interesting part: Complex and multicellular life could have appeared in such planet earlier as well. I dont know why but Earth had a full billion boring years without developing any noticeable life but evolution would take place faster in my planet. Since sunlight seen from this planet would look stronger because my host star would be brighter than the Sun the first animals in the sea would have appeared much earlier because the stronger sunlight would provide extra energy for the development of life. Oceans could evolve entire aquactic forests and as a result the sea could look green.

 

Land animals could have appeared earlier too: I believe these animals would look shiny and more colorful than the first land animals that appeared here on Earth because they would need extra protection from the F star's sunlight and the higher UV radiation. It seens silly but since sunlight would be stronger and more intense than the Sun it could reflect on animals color. They could be beautiful and exotic drawing a lot of attention.

 

Plant life could look exotic for us too. I read a PDF article saying that the peak wavelenght color emission of F main sequence stars are in the blue- cyan range. So the plants of a habitable planet orbiting a F main sequence star could look blue but I read in another article that plants in my hypothetical planet could be actually colorful having many shades of red, orange and yellow and this makes sense because here on Earth clorophill is green because it absorb blue and red light and reflect green which is located in the middle of the spectrum. So most plants here on Earth look green.

 

But on my planet orbiting the F star plant could have a wider range of colors because they would need to produce new pigments to protect them against higher UV levels. It could be shiny and reflective pigment which could make such plants a crystal/metallic look. These plants would look very different from the ones we have here on Earth.

 

Sunlight on such planet would look stronger to the point of being pretty unconfortable for us. It would be whiter too and the morning and sunsets would be probably light yellow rather than orange-red.

 

If there are people living in such planets I believe that their skin would look blue or somewhat metallic because they would need to produce a kind of metal-colored melanin that protected them from UV.



#2
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Due to the increased amount of radiation, I think that life would probably never leave the ocean.


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#3
CyberMisterBeauty

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Due to the increased amount of radiation, I think that life would probably never leave the ocean.

 

What if the planet had a thicker ozone layer or another gas that filter higher amount of UV radiation more efficiently?



#4
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Due to the increased amount of radiation, I think that life would probably never leave the ocean.

 

What if the planet had a thicker ozone layer or another gas that filter higher amount of UV radiation more efficiently?

Well, than life could more easily survive outside the ocean, so life would spread to the land eventually.


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