What would Earth be like if Theia hadn't hit it?

[Megalodon 720]

The most common theory for how the moon formed states that when the earth was young a Mars-sized planet collided with it, the cores of the two planets merged and the rest of Theia was destroyed and thrown into orbit. The debris then coalesced into one or two moons.

The moon today stabilizes the Earths rotation on it's axis so what would it be like if Theia had never existed and therefore never collided with it?

[Whirligig Girl]

Theia would have eventually hit us sometime. But let's ignore this. accelerate Theia to relativistic velocities in the other direction.

I also prefer to call pre-Theia Earth "Terra", because Earth is what we call a big chunk of rocket that has a moon and a big iron core. Terra would have never stabilized it's axis with a moon, and without an extra-hot, extra-large iron core, plate techtonics would never have formed. The earth would also be about 80% it's current size,so you'd may about 80% what you do on Earth. (unless I'm mistaken and the square-cube law breaks me.)

Life might still develop, but evolution; especially onto land; would be slower due to a lack of tides, but they would have to deal with 4 hour days, extreme winds, and massive climate changes. This might actually make evolution faster.

Small, but dense and heavy animals may roam the surface, but the winds would be too much for animals much larger than wolf-like species to keep from flying.

Intentional flight would be impossible, as the winds again provide a problem. Birds or bats would be tossed around too much to glide.

A lack of a hot core could mean a lack of greenhouse gasses, because they are released by volcanoes. This would make the overall climate of terra colder.

It's also likely that there was much more water on Terra than Earth, so there might not be a lot of land anyway.

If we image somehow Theia is actually put in a stable orbit, perhaps at Terra's L3, Theia would share a similar fate as Mars. Theia would have water, but then dry up. Due to it's proximity to the sun, it would actually be warm enough for water to be liquid. It would also be hot enough to evaporate into the atmosphere.

Here, Theia, Terra, and Mars share similar fates. Without a lot of gravity and without a magnetic field, they can't keep their atmospheres. Mars and Theia would be the solar system's rocky twins.

Venus would be the biggest rocky planet now. It does not have a magnetic field, but it does have lots of gravity and a much thicker atmosphere to begin with. It still gets to be a hot barren wasteland.

In the end, by the time we reach 4.5 billion years, We likely get a solar system with three small dead rocks and one large boiled rock. Maybe Europa or Enceladus will still get life. They'll be able to keep life for much longer.

[KerikBalm]

Theia would have eventually hit us sometime. But let's ignore this. accelerate Theia to relativistic velocities in the other direction.

Well... thats one way to deal with it... another would be to presume that Earth and Theia formed as one, farther than separately followed by a collision.

or... double planet! that would be so cool.

I also prefer to call pre-Theia Earth "Terra", because Earth is what we call a big chunk of rocket that has a moon and a big iron core. Terra would have never stabilized it's axis with a moon, and without an extra-hot, extra-large iron core, plate techtonics would never have formed. The earth would also be about 80% it's current size,so you'd may about 80% what you do on Earth. (unless I'm mistaken and the square-cube law breaks me.)

#1) If Theia was roughly 10% the mass of Earth (assuming mars mass), and the moon is just 1%, it seems Earth would have 90% of its mass, and thus 96% its radius...

#2) Earth already would have had a hot core, Theia would add some KE to it to warm it up, but that whole liquifaction and disrupting of the crust and hot debris into space probably made earth lose more heat than it gained from the KE impact. As its mass was only 10% of Earths, its core adding to ours was not needed, but sure, it helps (the core is mainly kept warm by radioactive decay, mainly)

#3) Unless a crust fracturing event is needed, plate techtonics would likely have already happened (noting that Mars has none, and Venus apparently had cataclysmic surface turnovers, maybe this would be needed)*

Life might still develop, but evolution; especially onto land; would be slower due to a lack of tides, but they would have to deal with 4 hour days, extreme winds, and massive climate changes. This might actually make evolution faster.

I don't see how that would affect the rate of evolution. If anything, its mainly changes in selection pressure that drive evolution(not counting genetic drift). Of course, a change in one species can put a selection pressure on another.

That said, tides would start selecting for a creature that may transition to land, but the overall rate of evolution wouldn't be affected much I think (especially since out of nearly 4 billion years of life, tetrapods only evolved 400 million years ago). I think arthropods still would have colonized land about as fast... the fish may have taken longer, if the arthropods had more time... maybe they would have evolved apatations that would prevent the new tetrapods from outcompeting them...

Maybe without tides, we'd be a "bug planet"

Small, but dense and heavy animals may roam the surface, but the winds would be too much for animals much larger than wolf-like species to keep from flying.Intentional flight would be impossible, as the winds again provide a problem. Birds or bats would be tossed around too much to glide.

Also the quote above... where do you get these extreme winds from?

The lack of a moon would result in more axial wandering, so climate changes would be less stable... but as a whole, the globe should be more or less the same, with the variation being more regional.

A lack of a hot core could mean a lack of greenhouse gasses, because they are released by volcanoes. This would make the overall climate of terra colder.

I see no reason the core wouldn't still be hot. Techtonics also plays a role in CO2 capture. Venus had plenty of greenhouse gas outgassing without a large moon.

It's also likely that there was much more water on Terra than Earth, so there might not be a lot of land anyway.

The LHB may have blown away the initial water anyway, and maybe this wouldn't have made a difference. The water we have now likely came after the LHB.

If we image somehow Theia is actually put in a stable orbit, perhaps at Terra's L3, Theia would share a similar fate as Mars. Theia would have water, but then dry up. Due to it's proximity to the sun, it would actually be warm enough for water to be liquid. It would also be hot enough to evaporate into the atmosphere.

Yea, atmospheric escape of most volatiles, only the heavy stuff (like CO2) would remain... and even then, not much.

Here, Theia, Terra, and Mars share similar fates. Without a lot of gravity and without a magnetic field, they can't keep their atmospheres. Mars and Theia would be the solar system's rocky twins.

Earth likely would still have a magnetic field, it would have plenty of gravity.

Venus would be the biggest rocky planet now. It does not have a magnetic field, but it does have lots of gravity and a much thicker atmosphere to begin with. It still gets to be a hot barren wasteland.

Venus is .8 Earth masses, without Theia's .1 Earth masses, Earth/Terra would be 0.9 Earth masses. Earth would still be bigger.

In the end, by the time we reach 4.5 billion years, We likely get a solar system with three small dead rocks and one large boiled rock. Maybe Europa or Enceladus will still get life. They'll be able to keep life for much longer.

I think Earth would still have life, it would not be "small", but bigger than your "large boiled one" (Venus).

What is this "still get life" for Europa and Enceladus... that implies they have life now, which is of course, an open question (I'm betting on No, but I would love to be wrong).

*

The principal difference between the two planets is the lack of evidence for plate tectonics on Venus, possibly because its crust is too strong to subduct without water to make it less viscous. This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field.[40] Instead, Venus may lose its internal heat in periodic major resurfacing events

[bsalis]

I also prefer to call pre-Theia Earth "Terra", because Earth is what we call a big chunk of rocket that has a moon and a big iron core. Terra would have never stabilized it's axis with a moon, and without an extra-hot, extra-large iron core, plate techtonics would never have formed. The earth would also be about 80% it's current size,so you'd may about 80% what you do on Earth.

Another possibility is that all the mass of Terra and Theia coalesced into Earth in a less violent way. So that the Earth would be larger.

[Jfjsharkattack]

Depends, If Theia just stayed out of the way, earth would be smaller, weaker magnetic field, less gravity, less water, but over all it would be fine while Theia would turn into a barren rock like the Moon and Mars Mashed together.

If Theia ended up orbiting Earth, It would probably be a binary system and be unstable, BUT it might work out and the back and forth large objects might generate enough tidal force to make both of the objects habitable. Or Theias core still freezes and its magnetic field ends and its atmosphere and water are blasted away. Still It would be interesting to have such a large object in the sky.

[JoeSchmuckatelli]

Quality necro.

9 years - but a worthy topic.

@KerikBalm is the only participant I recognize.  Nostalgia much?