lpetrich
Contributor
Our planet's oceans are very deep by ordinary standards. Their average depth is 3.7 kilometers, with a maximum depth of 11 km, at the Challenger deep. If spread evenly over our planet's surface, it would be about 2.6 km deep. But relative to the Earth's size, they are very thin. Scaling the Earth to the size of a giant beach ball, with diameter 2 meters, the oceans' thickness becomes 0.6 mm -- about as thin as the beach ball's plastic surface. By mass, the oceans are even less, about 0.023%.
Nearly all the Earth's surface water is in its oceans (Where is Earth's water? USGS Water-Science School), and how much is in the interior is something that geologists argue about a lot. But a rough guess is at least as much as is in the oceans, and I recall estimates like 3 to 10 times as much. That makes the Earth's water as much as 0.2% by mass. Still very small.
However, some exoplanets, like some of the TRAPPIST-1 ones, have sizes and masses consistent with their having much deeper oceans, like a few hundred km. If deep enough, these oceans will have a layer of high-pressure ice on their floors.
Planet Formation: How Ocean Worlds Happen mentions a recent hypothesis for what makes the different. Amount of aluminum-26 from nearby supernovae. This nuclide decays into Mg-26 with a half-life of about 717,000 years, so it would have to be produced by relatively recent ones. The heat from its decay would bake the larger protoplanets, driving off much of their water, and these in turn would make drier planets.
A water budget dichotomy of rocky protoplanets from 26 Al-heating | Nature Astronomy, [1902.04026] A water budget dichotomy of rocky protoplanets from $^{26}$Al-heating
PSRD: Dating the Earliest Solids in our Solar System
PSRD: Aluminum-26 Clock
PSRD: An Even More Precise View of Aluminum-26 in the Solar Nebula
One meteorite's grains formed over a 3-million-year interval.
Geological History of Asteroid 4 Vesta: The “Smallest Terrestrial Planet” notes some additional early-Solar-System radionuclides, like Mn-53, which decays into Cr-53 with a half-life of 3.7 million years, and Fe-60, which decays into Ni-60 with a half-life of 1.5 million years.
Vesta itself melted from radioactive-decay heating some 5 million years after it formed, and solidified not long after that. "Vestoids" are asteroids with very similar surface composition, and HED meteorites also have very similar composition. So those meteorites are pieces of Vesta in our labs
Meaning that what melted Vesta is what kept our planet's oceans from being superdeep.
Nearly all the Earth's surface water is in its oceans (Where is Earth's water? USGS Water-Science School), and how much is in the interior is something that geologists argue about a lot. But a rough guess is at least as much as is in the oceans, and I recall estimates like 3 to 10 times as much. That makes the Earth's water as much as 0.2% by mass. Still very small.
However, some exoplanets, like some of the TRAPPIST-1 ones, have sizes and masses consistent with their having much deeper oceans, like a few hundred km. If deep enough, these oceans will have a layer of high-pressure ice on their floors.
Planet Formation: How Ocean Worlds Happen mentions a recent hypothesis for what makes the different. Amount of aluminum-26 from nearby supernovae. This nuclide decays into Mg-26 with a half-life of about 717,000 years, so it would have to be produced by relatively recent ones. The heat from its decay would bake the larger protoplanets, driving off much of their water, and these in turn would make drier planets.
A water budget dichotomy of rocky protoplanets from 26 Al-heating | Nature Astronomy, [1902.04026] A water budget dichotomy of rocky protoplanets from $^{26}$Al-heating
PSRD: Dating the Earliest Solids in our Solar System
PSRD: Aluminum-26 Clock
PSRD: An Even More Precise View of Aluminum-26 in the Solar Nebula
One meteorite's grains formed over a 3-million-year interval.
Geological History of Asteroid 4 Vesta: The “Smallest Terrestrial Planet” notes some additional early-Solar-System radionuclides, like Mn-53, which decays into Cr-53 with a half-life of 3.7 million years, and Fe-60, which decays into Ni-60 with a half-life of 1.5 million years.
Vesta itself melted from radioactive-decay heating some 5 million years after it formed, and solidified not long after that. "Vestoids" are asteroids with very similar surface composition, and HED meteorites also have very similar composition. So those meteorites are pieces of Vesta in our labs
Meaning that what melted Vesta is what kept our planet's oceans from being superdeep.
