Recent comments in /f/askscience

forams__galorams t1_jbc9f59 wrote

Reply to comment by tomtom5858 in What happens at the end of a subduction zone? When the entire plate subducts? by kittens0423

> Yep. If fossiliferous rocks are subducted, the fossils will be buried in the mantle until eventually, those fossils are somehow transformed beyond being recognizable as fossils (i.e. they're mixed enough, melted or not).

Your use of ‘eventually’ is kinda misleading here. Any fossiliferous rocks would be at the top of a subducting slab and so if they didn’t get scraped off onto the overriding plate they would already be sheared upon entering the mantle; not to mention right at the slab-mantle interface where it won’t be long at all before the heat finishes them off.

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BiPoLaRadiation t1_jbc25hj wrote

Reply to How much influence does a natural satellite (like the Moon) have on the formation of continents ? by Aubin_kun

The moon was wildly influential on the formation of the earth as it is and life. And maybe had more significant impacts such as on the formation of plate tectonics but that isn't really known or not.

So as you may know the moon was formed through an impact event between proto earth and a roughly Mars sized planet called Thea. The result of this impact was, potentially only over a few hours to days, the formation of a relatively massive moon made mostly of lighter silica rocks and material. The majority of the metals and heavier elements in the core of Thea sunk to the core of the earth giving earth an oversized core compared to its size which no doubt has contributed to earth's excellent magnetic field. This has undoubtedly contributed to the formation and protection of life on earth.

So where did Thea come from? Was it launched from elsewhere in the solar system? Well it most likely formed in the same section of the protoplanetary disc as earth did resulting in it having a very similar orbit which eventually resulted in the two colliding as they migrated and shifted within that orbit.

Now let's talk about plate tectonics. Plate techtonics is a result of internal stresses forcing the outer shell of the planet to buckle and warp until some part of it sinks into the mantle and starts the conveyer that is plate subduction and plate spreading. It is responsible for the formation and break up super continents, building of mountain ranges and island chains, for mass extinctions and vulcanism, and for both massive additions of greenhouse gasses into and sequestration of green house gasses out of the atmosphere through vulcanism and plate subduction and weathering respectively. A useful way to look at plate tectonics is to look at other similar planets and see why they didn't form plate tectonics.

Venus is a great candidate. It is similar in size to earth with the only major differences being no moon and closer to the sun. It is theorized that venus failed to form plate techtonics due to that proximity to the sun. The sun heated the crust of venus enough that, when internal forces cracked and deformed the crust of venus, those cracks were repaired through melting and the deformation was more elastic resulting in smaller cracks.

If the crust had been colder the crust would've been more brittle resulting in less elastic deformation, larger cracks, and cracks that didn't heal as quickly through heat and melting. Because venus' crust never overcame this it never truly started the process of subduction and so no plate techtonics.

Interestingly enough the result of this was, we think at least, the build up of pressure and heat below the crust since there was no way to consistently vent and release this energy. Eventually this reaches a point where the pressure bursts forth causing some sort of chain reaction and resulting in what is known as a planetary resurfacing, ie the entire surface of the planet was simultaneously covered in massive lava flows pretty much all at once. The result in a massive release of volcanic gasses forming venus' current atmosphere and ensuring that venus would always be a hellscape planet with intense pressure and heat. It's thought this has occurred two or more times in venus' history. Earth and Mars have also had massive bouts of vulcanism, the largest of which on earth coincides with the largest mass extinction event in earth's history (the Siberia traps). It's possible that the trigger for such massive widespread vulcanism may have been a large impact event like what's theorized may have set off mars' mass vulcanism events.

Speaking of Mars, Mars never formed plate tectonics either. The idea for this is that it simply cooled too quickly. The heat and energy that causes buckling and deformation of the crust is caused by the heat released by the left over heat and radioactivity of the core. With such a small core Mars simply cooled too much before plate techtonics could get going. This is also why Mars has no magnetic field, the core and mantle has cooled to the point that the fluid dynamo caused by the different rotations of the core and the mantle material weakened significantly. All of this likely because Mars is just too small of a planet.

Now let's go back to earth and talk a but about the moon and plate techtonics. The moon may have contributed to plate tectonics in a couple ways. First and foremost it increased the size of the planet and the core significantly. The addition of so much heat and radioactive material no doubt helped provide more energy for internal forces to deform and crack the crust.

The moon may have also contributed to those forced through tidal forces. The moon is not only massive in relation to earth compared to most moons and their orbital bodies but it also used to be significantly closer to earth and orbiting much faster. Just after it's formation the moon would've orbited 15-20,000 miles away compared to its current 238,000 miles, would have been 15× bigger in the sky, and had an orbit just under 24 hours. While the moon would quickly move farther away from earth, the energy lost in that process was lost through tidal friction which would have contributed to the deformation and buckling of the crust (once it had resolidified).

The impact may have also helped earth avoid venus' fate. The early sun was significantly more luminous (and about 2-4 times larger) after it was initially formed and steadily decreased in luminosity until it was about 100 million years old. After which it has gained about 10% luminosity every billion years since. The moon formed 60 to 175 million years after the formation of the solar system. That may have helped the early earth avoid that period of intense solar energy that likely contributed to preventing venus from forming plate techtonics. The impact that formed the moon also imparted a huge amount of rotational energy to the earth moon system with a "day" just after formation being somewhere between 1.5 and 6 hours long. That quick rotation not only imparted a lot of tidal friction on earth but also prevented any one bit of crust from being baked by the sun for too long.

Venus in comparison has a rotational period of 243 earth days and will eventually become tidally locked with the sun like mercury is. Granted venus rotated much faster just after the formation of the solar system and had its rotational energy sapped away by tidal friction from the sun much faster than earth but the point still stands.

So all in all the impact that formed the moon is likely a significant contributer to earth's ability to start up the process of plate techtonics and undoubtedly contributed to the formation of life through its contribution to earth's magnetic field but also through the influence of tides as a driver of evolution and the contribution to earth's short day.

Now how does this help you with your divine punishment moon? Who knows. The moon maybe helped start plate tectonics but if you've got a super continent without one then it already exists for you. The majority of the ways the moon influences the evolution of the earth was in its cataclysmic formation event. If the formation is simply a snap of some gods fingers then most of this doesn't matter. If the people of your planet survive this formation then the formation will not be close to the formation of the earth, since the impact that formed the moon turned the earth into a molten ball for at least a couple million years before the crust reformed (and may have even turned the earth into a gaseous donut of vaporizers rock and metal for a little bit depending on how the impact happened exactly). If any life had existed it wouldn't have survived although that point is irreverent since life didn't form for several hundreds of millions of years after the formation of the moon and that was the most basic of basic life. Complex life took another couple billion years or so. So good luck with your world building. Hope my post helps at least with some ideas.

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Randvek t1_jbc0npw wrote

Reply to How much influence does a natural satellite (like the Moon) have on the formation of continents ? by Aubin_kun

Without the moon, the Earth’s tides would be greatly reduced. Shorelines would function more like lakes than oceans. This doesn’t change 99% of the continent, but would have a huge effect on the edges.

The moon is also responsible for stabilizing Earth’s tilt. Without it, Earth’s seasons would be different. Instead of four seasons to a year, we would have many more. This would make the habitable zone of the planet smaller, though being near the equator would still be safe.

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Wild_Sun_1223 t1_jbc0bez wrote

Reply to comment by Mr__Teal in When humans next land on the moon, will our telescopes from Earth's surface be able to photograph the rocket on the moon's surface? by Nswl

Yes, since a Earth day is 86.4 ks, then you can do it at a walking pace of 83 / 86.4 ~ 1 m/s, which is slower than average (1.4 m/s). But in practice you'll wanna sleep, so maybe two Earth days is better than one. Note that regarding oxygen, bottles could be laid out in advance similar to an Everest climb on Earth, and there could be a half-way camper for sleeping.

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Human1221 OP t1_jbbzwv5 wrote

Reply to When did this body type first show up? by Human1221

Major appreciation to everyone who commented, that gives me great starting points to read more. I was watching a science education channel on ytube recently that pointed out how many creatures are sort of morphs of the same basic internal bome structure and it was really wild to internalize that.

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