I have read the earth’s water (oceans, rivers, etc.) came from icy objects in space crashing into the early earth over millions of years.
Is here any competing theory (for example: a chemical process on earth that produces water?)
One theory suggests volcanism as a more likely source.
I’ve heard it came from space too, but where did that water come from and why is there more water here than on other planets?
An older form of photosynthesis also could’ve played a role.
It came from hydrogen and oxygen bonding in interstellar clouds.
Which planets are you thinking of?
Mercury is too hot. Any water would evaporate and escape.
Venus likely had a similar amount of water, but the heat put most of it into the atmosphere, where it was at risk of splitting into hydrogen and oxygen for long enough for the hydrogen to escape.
Mars has lots of water, if not as much as Earth.
The gas giants probably have water as well, although it’s hard to detect in all the hydrogen. Several of their moons are definitely watery.
Question is unsettled as of 2019.
Inside the Earth counts as on Earth as far as astronomers are concerned, so vulcanism is just rearranging the water that’s already on Earth.
The Big Splash, the collision of the proto-Earth with another planet very early in the history of the Earth, is thought to have removed almost all water from Earth. The stuff we have now is thought to have come by later and the question is usually about whether it came from comets or from asteroids. I suspect it came from both, which is making answering the question difficult if it’s assumed it came from one or the other.
Hydrogen is the most common element in the universe. Helium is second, and Oxygen third; everything else is substantially less common.
When our universe was born, it was, initially, too energy dense for the particles that make up atoms to form even hydrogen. The component parts were moving too fast and bouncing off of one another. The whole universe was filled with a sea of warm gas, essentially. But eventually the protomatter cooled enough to form atoms, which fell in under their own gravity to form nebulae, galaxies, stars.
When a bunch of hydrogen ended up in one place, it became a star. The hydrogen atoms underwent various fusion reactors, eventually forming heavier elements in the star’s core. These elements would slowly poison a star, causing the fusion that power it to falter. This leads to the still enormous mass of the outer layers of the star to fall in under their own gravitational attraction, as the atoms are no longer being pushed out by the energy released by fusion.
This is a supernova, and while a white dwarf or black hole is left behind, much of the star’s mass, both in light gasses from the outer layers and heavy elements from the inner layers, are flung out into space, forming nebulae.
Early in our universe’s history, supernovas were much more common. And one such nebula collapsed in on itself, swallowing gas and other materials. Most of the matter fell into our sun, but some - maybe .02% of it – ended up forming a “proto-planetary disk” - think of Saturn’s rings, but made of all the matter in our solar system aside from the sun.
Over the next few billion years, this ring of dust would collapse into the planets we know and love.
Not just Earth’s water, but our iron core, the uranium in our crust, the calcium in your bones… it all formed as the product of a fusion reaction around that long dead star. Even the comets that brought us water came from this same nova – they’ve just been orbiting very far out for millions upon millions of years before plunging in and smacking into Earth.
Everywhere closer than Earth, liquid water cannot exist, as it is evaporated by the sun. Everywhere further than Earth, water is frozen. So while other planets have been hit by comets too, Earth is the only one with liquid water.
Not too bad of a summary, but a few nitpicks. The planets and other non-solar stuff in the solar system are around 2% of the total mass (actually a bit less), so that number is off by a couple decimal points.
Not billion, a few million.
Not just a single supernova. I can understand where you got the idea, because I’ve seen quite a few descriptions of the formation of the Solar System that say that or at least give that impression. The nebula that collapsed and formed the Sun (and a couple thousand other stars) contained lots of atoms that were not hydrogen and helium. That’s how we see a lot of them. Bright stars illuminate these atoms in nearby nebulae, either as dust particles which reflect the light, or by ionizing individual atoms that glow when they reabsorb an electron.
At any rate, the interstellar medium contains the atoms given off by thousands, if not millions of supernovae. Also from kilonovae (mergers of neutron stars) and other sources. It’s mostly still hydrogen and helium but is enriched by all these other sources. In the spiral arms, which are density waves, the nebulae are compressed some, and then a supernova going off nearby will cause the collapse into stars.
There are other places in the Solar System with liquid water, but they’re under ice or rock which keeps it from freezing or evaporating away. Several satellites of Jupiter and Saturn are thought to contain liquid water under surface ice. Also there’s probably some underground water on Mars.
The other nits you picked are all totally valid, but I think we have to split the difference on this one – the number appears to be .14% of the solar system being outside the sun (99.86 is the number I keep seeing for the sun) so we were each off by 1 decimal point.