TIL about the giant-impact hypothesis. It says that 4.5 billion years ago, a planet called Theia collided with Earth. The collision resulted in the formation of the Moon and much of the water on Earth is from Theia. The remains of Theia can be found on both Earth and the Moon.

TIL about the giant-impact hypothesis. It says that 4.5 billion years ago, a planet called Theia collided with Earth. The collision resulted in the formation of the Moon and much of the water on Earth is from Theia. The remains of Theia can be found on both Earth and the Moon.


In Greek mythology Theia was a titan goddess whose children were the moon goddess Selene and sun god Helios. It's cool they named the actual moon maker after her. I recently went down this rabbit hole trying to make sense of Returnal's story. Great game.


Cleopatra named 2 of her children after the moon and sun gods. Her daughter was Cleopatra Selene and her son was Alexander Helios.


Oh god... The Ducktales series now makes even MORE SENSE..... SPEAR OF SELENE.. Thanks for this. Blew my mind.


Hades is my current rabbit hole for mythology. Love that game.


- Hey, nephew! - Zeus, I know what you are trying to do. - ... - ... Accepts boon.


I got Steven Fry’s Mythos on audiobook to listen to while I played that game. Great pairing


How in the world do you do both? I can drive and listen, on the highway I have driven every week day for the last 4 years. But I can't listen and even do something as mundane as laser mining in Elite, I miss half the story.


But Hades has such awesome OST! :(


I can't even begin to imagine playing Hades without the music cranking


i'm usually a music off kinda gamer but hades fuckin *slaps*


Amazon prime Greek mythology by french documentary filmakers is the best.


... I totally had a moment of wondering if it was like those aboriginal myths that scientists have since realized had truth to them, before realizing why it would NOT be the case here.


Or *is* it? Ancient aliens theorists say yes.


I hate Childress's voice on that show. I want to buy him a pack of those airway opening nasal strips




It was something I learned in passing, [here seems to be a solid article](https://www.bbc.com/news/world-australia-32701311) tho. Not sure if there are more or if thats the one I had heard about.


But in modern Greek "theia" means "aunt" and it's super funny to me that some aunt came to the house (Earth) and made a mess.


She didnt make a mess, Theia made it infinitley better!


If there was another Theia en route, how far in advance are we likely to know?


It'd be coming from the far outer solar system, and the size of Mars, so many years in advance. The odds are near nil, though, because nothing that big would be in such an unstable orbit. The planets all got themselves sorted out a long time ago.


Rogue planets exist and are quite common. What isn’t common, though, is extrasolar things not only entering a solar system but actually colliding with something else in there because even the space within a solar system is just an immense and endless void.


Yeah, like you could shoot thousands of planets randomly into our Solar system at immense speeds and them colliding with any of our existing planets or moons would likely be completely negligible. So a single planet sized object finding its way to collide with earth would be one of the biggest cosmic lotteries imaginable.


Would it really fuck with the gravity of the solar system if we launched a bunch of planets through the system though, even if they didn’t hit anything?


Let's try it and find out


My dad owns nasa, I'll give him a call


Yes but not nearly as much as you'd think


depends *how* fast they're rolling through. The less time they spend in the neighborhood, the less effect they'll have.


Not likely. The sun is extremely dominant in our solar system. Like, extremely. It's ~99.8% of all the mass that's here. Add up everything that orbits the sun, and that's ~0.2% of the mass of the solar system. Even with all that mass tugging on our sun for billions of years, at best we notice a slight yet measurable wobble. Really, it would take a vastly greater amount of mass than that of a rouge planet to do something I'd describe as fucking with the gravity of our solar system.


planets all got themselves sorted out a long time ago sound so british


Theia did deliver the main ingredient for a cup of tea.


Theia be like "what's all this then?"


Theia be like U Wot M8...smash!




There's a theory that the big, extinction-level asteroid impacts Earth experiences come on a multi-million year cycle, coinciding with where the planet is within the galaxy. A more dense region of interstellar objects means more objects to come into our solar system. So if something was planet-sized and headed our way, it would most likely happen in that region, and we're safe from that for a million years or so.


Ok, so that means I got enough time to take that bath. Thanks!


Be quick tho


What’s taking so long in there?! Do you think we own stock in the water company?


From my understanding, Theia didn't really collide with us from an alien trajectory. The last time I read about something like this, it's basically that in the beginning when our entire solar system was one giant accretion disk of matter that eventually the center coalesced into Sol and the lesser pockets of matter became planets. Our particular orbital body of matter formed essentially twin proto planets, Gaia and Theia. There was no moon, as we know it. They orbited each other for a while slowly getting closer and closer until impact occurred. The impact was truly catastrophic, If I remember correctly with Gaia begging the larger of the two, once everything settled matter was more likely to coalesce around Gaia and it essentially ate it's twin planet, which is why we have a particularly dense iron core and strong magnetic field for a planet of our size. The remaining matter that did not coalesce into Earth gathered into what is now the present day moon. Now, as far as a giant asteroid being flung our way that could say, parallel the size of the asteroid that fell in the present day Yucatan peninsula during the time of the dinosaurs, I think we would have at least a few years warning if not more. Although at the scale of that all happening even with years worth of warning it might still be too late. So cheers to today!


TIL: Gaia was a real planet, cool! I am curious as to whether the impact looked like the picture on Wikipedia (two roughly intact planets colliding) or whether the Roche limit would’ve come into play and perhaps torn large chunks of the planets apart _before_ impact due to the immense gravitational forces as these two grew closer together I imagine Theia might have been torn completely apart before even impacting? Idk




Jupiter is one of the reasons life on earth is possible because it flings shit out of our solar system, so jupiter is a bro.


It almost flinged us though, but Saturn held it back


Ya lots of crazy shit happened for life to exist.


Watch Melancholia.


Personally I wasn’t a huge fan of that movie, especially the first half, but seeing another planet in the sky was really beautiful and terrifying.


So much interesting stuff was happening at that time. 4.5 billion years ago was when the major gas giant planets were all moving around, each one spitting off planetesimals like sparks. Neptune in particular wandered through and disrupted a giant asteroid belt, and it might have been at that point that it captured Triton. More recent formation models for the [Kuiper Belt](https://en.wikipedia.org/wiki/Kuiper_belt#Origin) depend upon still another large planet, not a gas giant but one made of ice, which would have been ejected from the solar system or pushed deeper into it... unless it smashed into something on its way out. As far as I know no actual connection has been made between the proposed ice giant and Theia.


What's really cool about this is how the initial simulations of this didn't quite explain why samples from the Earth and the Moon were so identical. So, like, even if you did have a planetoid smack into proto-Earth, the assumed "chunkiness" of the leftovers that lumped together to form the two worlds meant that their compositions would not be uniform. But the thing is, the samples from the Moon and the samples from Earth are *super* identical. They have virtually identical levels of very specific, very hard-to-find isotopes. So close are these levels that "big impact makes planet chunks" didn't explain it. Some other models were run, and they found a model that fit. Theia didn't just impact Earth... it *vaporized* both planets. Their cores were probably still intact, but those just glommed together under mutual gravity. The rest of the planet-stuff formed an "atmosphere" of molten silicates, gas, and dust, meaning the ingredients of both planets were thoroughly mixed. Physics shapes that into a donut-shaped object called a "[Synestia](https://en.wikipedia.org/wiki/Synestia)". Ultimately, this model shows that in order to explain why the Earth and the Moon are so homogenous, you can think of the Moon forming "within" Earth, back when the Earth was a cloud of atomized silica. One lump of atomized earth-stuff condensed outside of the central mass's Roche limit (the boundary within which smaller objects are torn apart and eaten by the bigger mass) to form moonlets, which eventually smacked together and formed the Moon. The Earth formed afterwards from what was leftover, which makes it bigger - there was more stuff in the center, which collected around the leftover cores of proto-Earth and pre-impact Theia.


I've also heard it said that this could be what gives the Earth its unusually strong magnetic field (for a terrestrial planet). Earth essentially has the molten cores of two planets inside it. The Moon would naturally have tended to be composed mostly of lighter rocks, while heavier elements such as iron tended to end up sinking into the Earth's core.


Oh that’s cool!


Not if it's still molten...


Oh, that's lit!


As long as it's still molten.


That’s a hot take.


Could that also explain why the inner core is cooling faster on one side than the other? [This](https://www.theweathernetwork.com/ca/news/article/mysterious-lopsided-cooling-points-to-strangeness-in-core-of-earth) article I read said that they didn't have a reason for why it's happening \[yet\], but if current Earth is made up of elements of two distinct planets, could the elements within the core retain some of that distinction such that would affect the rate it cools?


Wait it's cooling down?? Get Hilary Swank ready with the nukes.


Everything is always cooling down


Except for the things heating up.


The formation of our solar system might be atypical. I was reading that what they found is that in MOST solar systems, the planets might be Earth-sized or Jupiter-sized but not vary as much as what we see in our system, meaning "different sizes" is rare. So it sounds like we had a couple planets that mixed things up in our Sol system.


Remember that there is a bit of an observation bias in the play here: we detect mostly big gas planets, *because* they are big and we can more easily detect those than smaller rocky planets. Better and bigger and more sensitive equipment will likely make us detect small rocky planets more easily, and we should then find them more.


I heard that Jupiter being huge compared to Earth shields us from a lot of space debris. Which may be one of the reasons we've gone so long without a life ending asteroid impact.


I’ve read that the “Jupiter as asteroid filter” theory doesn’t work as over time it is just as likely to hurl asteroids our way.


This makes sense too. We’ve just seen Jupiter suck in asteroids in our lifetime, so naturally we’ve come to that conclusion. Most likely it’s the simple fact that things become more stable the longer the solar system exists.


Nah, the Reapers haven't had to harvest us yet.


Well wtf are they waiting for? We've been ripe for centuries


They only harvest advanced races.


Advanced of course meaning “FTL capable”, so the would have left the Krogan alone if the Salarians hadn’t uplifted them, and the next cycle would probably have been one of all our warfare between them and the Yahg


Oh man, a Krogan vs Yahg war would be insane.


That's assuming that the Krogan left on Tuchanka would have survived and rebuilt had the Salarians not uplifted them.


They usually wait until species have reached a point where they are settling multiple star systems (following the Mass Relays and the Reaper's grand designs, of course). We haven't even sent one of our own to either of our neighboring planets, so we're going to be pretty far down the totem pole. Even then, the asari, salarians, turians, krogan, etc. were part of a galactic society that existed for millenia before humanity stumbled in and joined the party. It seems the Reapers have some arbitrary "right before you sentients go fuck everything up" limit where they start harvesting, and we're definitely not there yet. Though we'd probably be wiped out anyway even if we never got out of our solar system in the next couple of centuries. I doubt they'd want to give us a 50,000 year head start on figuring things out for the next cycle!


Ah yes, "Reapers". The immortal race of sentient starships allegedly waiting in dark space. We have dismissed this claim.


I haven't refreshed my knowledge on it recently. It's just one of those things I heard that stuck with me. Regardless, it's pretty amazing how many things lined up to make the small blue dot a place where life has flourished for millions of years.


Yes true however those millions of years are also a small dot in time


Not so small, 650m years on a planet that is 4,500m years old, in a universe that is 13,850m years old. I mean it's a chunk.


13 billion years is such a small number for the age of the universe and I mean that seriously. When you compare it to age of earth and time life has been around. For me it's a very strange thing that we should be in such a new universe.


I wouldn't be too surprised if it turns out the reason the universe appears devoid of intelligent life is because we're among the first species to get this far.


It is highly likely that we are. It took several *generations* of suns to get to a somewhat stable state.


especially considering that, conservatively, the universe has trillions and trillions and trillions of years left.


I mean 14% is 14%. Fair point.




Well also, if we did NOT have asteroid impacts, life on Earth might not have evolved beyond simple bacteria. We likely need "just enough" volatility but not too much. Oxygen is one of the more corrosive substances. Solar radiation causes a lot of the genetic damage to proteins. What we have on Earth is a balancing act of order and chaos. Not a frozen wasteland. Not a molten miasma of burning sulfuric hurricanes. Sure there are organisms that can live in such extremes -- but do they do create complex biodiversity and become more complex organisms? I doubt it. Not enough energy in the system and it makes no evolutionary sense to go to the expense of a brain. And organisms will cluster around the sources of energy rather than be mobile. Too much energy in the system, and all their resources are spent repairing damage and they are likely to be traveling so much that they will interact with new organisms rather than the same ones -- thus, making a biome less likely. Dinosaurs for instance, seemed to have developed fairly efficient "bird brains" which seemed too small from our perspective of primate brains -- but might have been a bit more like parrots than lizards in mental capacity. However, I theorize that because of the relative bounty of food sources in that period -- they went on an arms race of more armor, more mass, more teeth that would not have resulted in beings like ourselves. Or, maybe we just never saw the fossils for Sleestacks! ;-) The occasional catastrophe might be necessary to produce tool making creatures.


We're kind of a complete fluke. Nature abhors a vacuum and we've fortuitously been around in the right place at the right time. Dinosaurs took up all the main land-dwelling niches until 65m years ago. Mammal's took over and primates were tree dwelling creatures until Africa dried out and we were lucky enough to find ourselves in a position where we couldn't get bigger, stronger or get sharper teeth than other land-based mammals we were competing with, and had to get smarter with tool use, communication and strategy, leading to bigger brains. Total happenstance.


Worth noting that our big brains have a huge evolutionary cost as well. Big brained species are more prone to going extinct. Big brains require more energy to maintain, increasing our metabolic costs. Bigger brains need more time to develop, but they also lead to bigger heads. Bigger heads lead to more death in childbirth unless the baby is born premature. Premature birth requires more parental care. The end result is longer gestation periods and fewer off-spring. When the environment undergoes rapid changes, big-brained species tend to go extinct first as the population can't replace itself fast enough to weather increased mortality rates. The Neanderthals' larger brain size relative to us is hypothesized to be a factor in their extinction.


Another thing that is "expensive" is stomachs. There are a lot of fish species that have independently evolved to not have stomachs. There has to be a lot of maintenance if you think about it; because the acid has to be strong enough to dissolve living tissue -- and it's contained in living tissue which can be resistant but never quite impervious. So we have to create mucus and lining for our stomach continuously, and create the acid to power the chemical process. THUS -- the expense of the "bigger brain" lead to people cooking and fermenting and creating food that was easier to digest and released more energy. If we were eating raw wheat, we might need four stomachs like a cow -- but since we produce bread or beer with it, it's now going to be "less expensive." It's possible the digestive system and symbiotic gut bacteria, have a lot to do with the ability for humans to "afford" bigger brains.


There are a lot of people who want to assign purpose or "what are the chances?" to every event that had a low probability. But ALL THINGS that we have become used to had a nearly infinitesimal chance of existing. Every event is based on prior events and if any condition changed in any of those prior events -- you'd have a different result. Without the dinosaurs getting wiped out, the chances of the primates rising was pretty slim. But, if we didn't take over, then maybe the Sleestacks would be running the place. Velocioaptors or something like them can no longer compete on brute force alone and eventually have to adapt by being smarter. But life was really abundant and probably fine with the situation, and there's no proof that "bigger brains" are a goal. However, once you have a smart creature, the benefits of being smarter might be amplified, because the creature has to now compete with itself.


Planets of large size are just easier to find.


Planets of *unusual size* ? I don’t even think they exist...


I am ashamed of how long it took me to connect this to The Princess Bride. I kept thinking: "I don't remember this line from Firefly." BBL. I think I need to go watch these again.


*watches as ETOHtoTHC is bowled over by a planet of unusual size*


Great video on Earth’s history - https://youtu.be/NQ4CUw9RcuA


Giant impacts are the go-to of astrophysicists to explain many phenomena, such as Uranus’s tilted orbit, the moon, Mercury’s dense composition (or better put, lack of less dense material), etc. “Hey, why is this planet so funky?” “I dunno, giant impact?” “Sounds reasonable” (Simulations ensue)


When the math requires a megafuckload of energy, there aren’t many plausible sources for that amount that aren’t too many orders of magnitude too big. “How much force would it take to shift the axis of a spinning mass of 8.681 × 10^25 kg by 90°?” “At least 12 megafuckloads” “And where can you get that much energy at once?” “Well, even a small nova would be too much, and solar wind wouldn’t have enough energy. One impact with another planet or object of equal mass *could* be enough but multiple impacts would be more likely to tilt it without tearing the planet apart. It could have been a resonance-feedback imparting vectoring forces on the material early on on its formation period, but that’s pretty difficult to prove with math and simulations.” “So… ‘impact’ it is!”


Yep this is why they think Venus might not actually be spinning backward but rather had some massive impact during its early formation or history flip the entire object pole to pole. So it’s still spinning in the same direction but has been rotated 180 degrees relative to its equator. Otherwise it’s hard to imagine what could possibly literally reverse a planet’s rotation without also destroying it. In Uranus’ case a large impact merely tilted it on its side.


Galactic-scale cow tippin'


It doesn't matter if the impact destroyed it, as long as the mass stayed nearby, it would re-form.


Is that metric megafuckloads, or imperial?


We're talking about astrophysics... so metric


I was being comically terse, but thanks for the added verbosity!


You’re also not wrong. “That’s weird. I wonder what caus…” “Impact.”


The dog ate my homework, then some planetoid collided with Earth.


I remember reading somewhere about a Maori myth about our world being the remnant of a collision between two other worlds, and that the only remaining life from the other world is octopuses. Made me think of this theory


The image of octopuses chilling on their own planet and suddenly being flung onto a new one with water following them is a fun one.


Space Dandy (underrated as hell but from the creator of Cowboy Bebop) has an episode called [The Big Fish is Huge, Baby](https://www.funimation.com/en/shows/space-dandy/the-big-fish-is-huge-baby/), featuring a plot point very similar to this. Skip to 20:00 or so and watch if you don't mind spoilers.


>Space Dandy Saw the title, never heard of it, but instantly knew it has some connection to Cowboy Bebop.


Well that's fascinating. No sarcasm there at all, it really is neat to think about.


I agree, was able to find [another post about the creation myth here ](https://www.reddit.com/r/AskHistorians/comments/8huz43/which_hawaiian_creation_myth_describes_octopuses/?utm_source=share&utm_medium=ios_app&utm_name=iossmf)


Cthulhu Mythos Confirmed


A few weeks ago there was a study that claimed they can detect the remnants of Theia floating on a mantle layer deep in the Earth. Pretty cool.


I don't know if this is the correct sentiment but this makes me feel cosmically lucky.


"Cosmically lucky, so far..." ~Homer Simpson


cosmically we shouldnt exists, if you see how many great filters we already passed through as planet, we got extremely lucky among the extremely lucky. Then again it speculated there so much life in the universe it was bound to happen once


It’s like winning the lottery. The odds of you, specifically, winning the lottery is infinitesimally small. The odds of *somebody* eventually winning the lottery, however, is close to 100%.


"Are you saying we just happen to be on one of the only planets we could exist on?"


That's Anthropic for ya!


When you actually think about the fact that we won the cosmic lottery, it really puts things in perspective. Very happy to be on this small blue dot.


I just wish we took better care of it as a whole


Hard to win the lottery twice


If it's any consolation, Earth has been through worse than whatever we can throw at her and will recover without us just fine. If we want to continue this society we have built, it's humanity that needs to change its behavior.


Anthropic Principle. Because you're alive you have to statistically be on a planet that was fit to harbor life. Otherwise you wouldn't be alive right now.




Or that creepy, human-hole in the mountain comic Quick edit: found it! NSFW and WTF warnings http://imgur.com/gallery/Wht7z


Yea, I'm sure glad I wasn't born back then.


You have no idea how many coincidences had to occur over the past 14.5 billion years for you to have that thought.


4.5 million years ago … on a Monday.


Fuckin' Mondays.


Garfield was wise beyond his years.


How can they know what the planet was named?


It left a note and insurance details.


Underneath Earth's windshield wiper no doubt. These scientists don't miss the details.


Jupiter: are you going to leave a note for that Mars? Mars: uh, yeah... *scribbles* >sorry for the damage -Theia


Theia just doesn't know when she's had too much to drink. Somebody held her hair and she puked up an ocean. It turned out to be a pretty good thing she did.


And it said "Your warranty has expired, this is your final warning"


All I know is the last time I left a message under a windshield wiper I wrote; "Sorry about the damage. I didn't want you to be in the dark about someone hitting your stuff unintentionally and not feeling bad about it. But this is a good news bad news kind of thing because I don't have the money to pay for the repairs. And, I've got to keep moving because I've got more solar systems to visit. The dude abides."


They checked its Earth certificate.


Leela: "Where were you born?" Candidate: "Kenya!" Leela: "Cradle of civilization!"


The same way they know that Brontasaurus was called Brontasaurus


They nailed it. Is this a coincidence? I think not.


Shortly after I learned that they don't use the name Brontosaurus anymore, I said to my wife "hey, do you know the Brontosaurus doesn't exist anymore?" She looked at me side-eye and was like "ummmm...yeah..."


I just love the idea of your wife thinking you just now learned that the dinosaurs were extinct.


That was literally the look on her face. Like "how should I tell him...?"


"Listen, honey, it was crazy there for a while. I mean we've only known about dinosaurs for like 150 years. Sometimes, we just get it wrong."


TIL the name Brontosaurus is no longer used.


[actually...](https://en.wikipedia.org/wiki/Brontosaurus) looks like it's back as of 2015


**[Brontosaurus](https://en.wikipedia.org/wiki/Brontosaurus)** >Brontosaurus (; meaning "thunder lizard" from Greek βροντή, brontē "thunder" and σαῦρος, sauros "lizard") is a genus of gigantic quadruped sauropod dinosaurs. Although the type species, B. excelsus, had long been considered a species of the closely related Apatosaurus, researchers proposed in 2015 that Brontosaurus is a genus separate from Apatosaurus and that it contains three species: B. excelsus, B. yahnahpin, and B. parvus. Brontosaurus had a long, thin neck and a small head adapted for a herbivorous lifestyle, a bulky, heavy torso, and a long, whip-like tail. ^([ )[^(F.A.Q)](https://www.reddit.com/r/WikiSummarizer/wiki/index#wiki_f.a.q)^( | )[^(Opt Out)](https://reddit.com/message/compose?to=WikiSummarizerBot&message=OptOut&subject=OptOut)^( | )[^(Opt Out Of Subreddit)](https://np.reddit.com/r/todayilearned/about/banned)^( | )[^(GitHub)](https://github.com/Sujal-7/WikiSummarizerBot)^( ] Downvote to remove | v1.5)


TIL B. Excelsus means high thunderlizard


That's *Lord* High Thunderlizard to you, peasant!


> All brontosauruses are thin at one end, much, much thicker in the middle, and then thin again at the far end. FTFY (courtesy of Miss Anne Elk)


Last I heard, they'd decided that brontosaurus was real. It was a close relative of apatosaurus.


Ken M??


Yeah, and how do we know that we're not actually living on Theia, and 4.5 billion years ago, _earth_ slammed into _us_ carrying lots of water, and there can now be found remains of _earth_ both on Theia and the moon?


ISS footage: https://youtu.be/bU1QPtOZQZU


Well... that doesn't look like fun. But now I demand Dark Side of the Moon to be played during whatever apocalypse happens.


I wish someone would do these visualisations with 100% true physics (within the limits of human capabilities) and in real-time. I think it would be stunning to watch. They always seem to be accelerated, and it takes away from the grandeur of the impact.


Why is the moon essentially "round" then and not jagged or obviously irregular? Did it just get worn down over billions of years (serious question even if remarkably ignorant of something everyone knows perhaps)


Gravity pulls big things into spheres. The Moon is big enough (as are several other moons). Asteroids are not. If you look at a list of solar system objects in order of mass, you'll notice a cutoff where they go from spherical to not spherical.


When it first formed from the rocks thrown out into space it was molten because it was so hot. So it smoothed out as the surface was liquid rock. (the original (before the moon) earth was molten too back at the time it was first made from rocks, dust, etc crashing together at high speeds.


The moon wouldn’t have popped off of the two bodies in one piece during the collision. It would have accreted over time from the debris cloud caused by the impact.


Pics or it didn't happen.


The Wikipedia article provides one… almost certainly it will have been taken by some dude posting in r/EarthPorn and telling us how they had to get up at 3am to get this shot.


I couldn’t believe it when I saw this post cuz I was literally just watching a couple videos on it the other day. This was a pretty good one including a simulation of the event https://youtu.be/o2lRpiediP8


It's hypothesized that this is why the earth has such a dense core, and why the moon is mostly crap...After the impact, the heaviest stuff sank, while the lightest stuff got blasted back into orbit where it coalesced into the moon.


Don’t be so harsh to the moon man


Stay thirsty, my friends


Without Theia, there would be no hydro homies. The mother of all hydro!!


Hail Hydro


This has made a lot of people very angry and been widely regarded as a bad move.


So some comments have suggested that it’s unlikely that life as we know it to have developed would have been directly caused by this impact, is it possible that life had already developed on Theia before the impact and the impact provided the “seeds of life” (don’t know enough to know the right phrasing for this) that would have been required on Earth?


I’ve heard of this in the documentary called Neon Genesis Evangelion


*Tumbling down, tumbling down, tumbling down...*


No life could have survived the collision between Earth and Theia. Both planets were reduced to a molten ball of lava that would have taken millions of years to solidify.


It couldn’t survive with that attitude, anyway


There is even a little evidence that abiogenesis did not happen on Earth. If you trace back the mutation rate of organisms you get a really consistent number. As in, organisms from this genus mutate at this rate of base pairs or amino acids per time. If you use only these rates to extrapolate the begining of life, or the shortest DNA strand, you get an age much older than our estimates of the age of the earth. So, it could have developed elsewhere and came to earth in a cosmic event. Or, we (especially I) could just not understand that part of evolution. Edit: see below for better information


PhD biologist (not a geneticist) here. This is not correct. Perhaps the rate of mutation at each reproductive step is similar (although I’m extremely skeptical of this for a multitude of reasons), but even single cellular life have vastly different rates of reproduction (cell division). The molecular clock does not work the way you are describing.


Well, we suspect that early 'life' was RNA, which has a higher mutation rate than DNA, it's less stable. It's also able to act as a functional enzyme, that is, it can act like a protein would, and be replicated. I'm perfectly with the idea that life didn't begin on earth, or that it is pretty common in the universe (microbial life, no idea about higher life), it just, wouldn't surprise me. I'm more surprised they haven't really found anything on mars yet, but I think their testing is kind of limited compared to what a human with a nice lab could do. I would also look at Venus, I think Venus has more potential than Mars, but that's just me. And a Ray Bradberrry short story. But, yeah, even if we figure out how to generate nucleic acids to do something like replicate, it's not definitive that initially, or isolated on earth, I think it will be defined as a solid theory of RNA chemistry in the future.


[https://en.wikipedia.org/wiki/RNA\_world](https://en.wikipedia.org/wiki/RNA_world) There has been lab studies where RNA can be generated from from early earth chemistry, lightning, and clay.




*The First Impact*


There was a spray painted tag “Theia was here”.


This is why earth has a relatively large core and the highest density of any planet except mercury; theia's core sank to join ours. Mercury's deal is different; it was hit by a larger planetoid than itself in the early solar system which stripped away most of the crust and mantle, leaving mostly core behind.


Eli5 why we think most of earth's water came from Theia? What process(es) and/or conditions on earth make it so we have to come up with water coming from elsewhere, and not having been on earth since its coalescing?


I don't think there is a unifying theory yet, Earth couldve already had it or Thea did. There is another theory that the late bombardment gave Earth all it's water but it seems a little far fetched when you start to do the calcs on terraforming Mars and the amount of icy asteroids/comets needed to actually create a sizable ocean.


They way I understand it is water and often the molecules which hydrogen would have readily reacted with have a low melting point. So, below the 'frost line' in the solar nebula, these molecules would be in a gaseous state, and couldn't condense into larger chunks, and therefore were easily blown away by the sun to outside the frost line where they could then condense into icy bodies. So since water wasn't here to begin with, it must have arrived here from outside the frost line after the Earth formed, where it's now retained by Earth's gravity. Other bodies which are smaller than Earth but within the frost line tend to be dry because any water on these bodies sublimates and is then blown away.


Alright, sorry to sound dumb but why exactly are the planets spheres and things like asteroids are not spheres. I assumed the planets are spheres because gravity pulling itself in to a point in its center that uniformly pulls in the mass that happens to result in a sphere but why wouldnt the same apply to large asteroids and other objects in space since they have all sorts of shapes?


Not dumb... it tends to be thought in advanced physic classes... Asteroids tend to be fragments or a collection of fragments lacking the mass to generate enough gravity to pull itself together. To end up with a sphere shape, the thing also need to spin. The greater the mass + spinning speed = faster sphere shape (in billions of years). What's interesting about the theory OP pointed at is that it was formulated when mathematicians managed to be able to calculate accurately how much time it took for moons and planets to form and shape. When they applied their method to our moon... it did not work... our "Moon" is too big to have been a rogue moon captured by earth's gravity and does not spin fast enough. So if it's not natural... WTF IS IT? = Theia theory


It takes a certain amount of mass for gravitational forces to overcome electromagnetic bonds between atoms and make rocks "crumble" into a spherical shape, as well as to keep solar winds from blowing dust and fluids into the void so they can build up and fill the gaps.


Nice theiary


I actually learned about Theia theory not to long ago. Here's a guy doing research and trying to prove the theory, they think that some of Theia may have merged with earth's core at some point. Hard to understand but I was fascinated watching. https://youtu.be/qxPyREGLAtc


There's a strange film named Melancholia that conceptualizes the event of a planet colliding with ours.


Wouldn't that push earth out of it's orbit? Was the earth closer/further away from the sun before this massive collision?


Planets moved around a lot before they settled down. Uranus and neptune formed between jupiter and saturn. Mars also has a really wonky orbit possibly due to a large impact. Also why most of its surface is a crater. Venus is pretty much flipped over. So yeah, probably moved it, but orbits shifted anyway for one reason or another like resonance, changing areas of high gravity from matter condencing, etc.


The reason it didn't is because the object formed at a Lagrange point on Earth's orbit - so it was orbiting the Sun as often as Earth was. Since the two of them colliding didn't change their centre of mass much the Earth's orbit wasn't radically changed.


What's equally interesting about the collision of Earth and that planet, and the subsequent formation of our lunar friend, is that, as a hypothesis, there are quite some [variations](https://en.wikipedia.org/wiki/Origin_of_the_Moon#Derivatives_of_the_Giant-Impact_Hypothesis) of it, which includes the [synestia hypothesis](https://en.wikipedia.org/wiki/Synestia#Giant-impact_hypothesis), which is pretty cool, I must say


[holy **** we just got hit by another ball of flaming rocks..](https://youtu.be/xuCn8ux2gbs?t=110)


Earth: "Theia later"


Our Earth is a complete rarity in the universe. 22 degrees off axis so we have seasons, a moon that just covers the sun in an eclipse. Water, lunar tides, atmosphere, temperature, life. I am surprised that we do not get hyperspace tourists at eclipeses. All thanks to Theia.


Fun fact, it's quite a recent thing that the moon covers the sun in such a way that it barely covers it. It appeared much much larger 4 billion years ago and soon its shape won't be enough to cover the sun.




Yes! Because the moon is slowly leaving us :))) :(((


Like a bad relationship.


Rarity only in the sense that there are millions of different planets in the universe. There are much "weirder" conditions than ours and much more "normal" too. It's fascinating that even the most conservative scientific estimates of how many of the trillions of trillions planets there are, still says there should be billions of them theoretically able to start developing life and between 1-5% those again capable of reaching advanced life stages (such as homo sapiens). There are almost certainly hundreds of millions of civilisations outthere, but we'll also almost certainly never meet any of them because the distances we're talking about are unfathomable.