3.2 billion years ago the Earth may have looked a lot like Kevin Costner’s ‘Waterwor

[GordMay]

Today, oceans cover more than two-thirds of the Earth's surface; but 3.2 billion years ago, our planet may have had virtually no land at all.
A recent study [*1] looked at ancient ocean crustal rocks, now exposed, in the remote Australian outback ( Panorama). It holds evidence that suggests any bits of land, that may have been protruding, from the vast oceans covering Earth 3.2 billion years ago, would have been sparse.

The team figured out these rocks had much more of the heavy oxygen-18 isotope, than oceans do today, and that turned out to be critical information.

Oxygen comes in two stable versions or isotopes, the heavier oxygen-18 and the lighter oxygen-16.
When rain or snow falls on continents, clays and soils take up oxygen-18 more than oxygen-16, leaving the water that returns to the ocean depleted in the heavier isotope.
There are a couple of potential explanations for why the oxygen isotope composition was much higher 3.2 billion years ago, than today, but the simplest explanation, is there were no continents above sea level.
If there are no continents above sea level, no weathering, no soils, no clays, all that heavy oxygen-18, that would otherwise be in the continents, stays in the ocean. And that's exactly what they found at Panorama.

“Limited Archaean continental emergence reflected in an early Archaean 18 O-enriched ocean” ~ by Benjamin W. Johnson and Boswell A. Wing
[*1] ➥ https://www.nature.com/articles/s415...rer=www.cbc.ca

[anotherT34C]

Interesting. I wonder what the feasibility of a true waterworld would be. 3.2GYA is in highly speculative territory regarding the continent configuration. I know they were believed to be very shallow, with only one largish landmass ‘Ur’ at the time. Ocean currents would be free to flow, and so the ocean temperature would be quite warm. But... the moon was significantly (10%) closer at that time, and the tides were more severe. I’m wondering if dry land being ‘dunked’ twice a day would also lead to their findings.

Thanks for linking the paper.

[a64pilot]

I still want to know where the water came from. Apparently at one time this the Earth was pretty much molten and had no atmosphere, so where did the water come from? Millions of cubic miles of water?

[MicHughV]

...I was piddling around the internet the other day and came across this presentation that depicts planet earth in scale to the " known" universe. Our piddling little planet, earth, is smaller than a dust mite in the grand scheme of things..nay...even smaller than that...so who really knows...
...these wild arsed guesses of 3.2 billion years is about as fanciful as one could possible imagine as there is simply no way to accurately estimate such a fact.
..we should be grateful that there is in fact water on our planet....otherwise one fact is for sure.....we'd be toast....burned toast at that:-)

[anotherT34C]

Originally Posted by a64pilot

I still want to know where the water came from. Apparently at one time this the Earth was pretty much molten and had no atmosphere, so where did the water come from? Millions of cubic miles of water?

My understanding is that the water came from comet bombardment in the early solar system.

[Pegu Club]

Originally Posted by anotherT34C

My understanding is that the water came from comet bombardment in the early solar system.

I read the same information some years back, in such case we should still be gaining water but at a notably slower rate, being that comets are still hitting our atmosphere, and literally raining down on us.

[anotherT34C]

Originally Posted by Pegu Club

I read the same information some years back, in such case we should still be gaining water but at a notably slower rate, being that comets are still hitting our atmosphere, and literally raining down on us.

We’re also losing water as it escapes from the atmosphere (this is why Mars is apparently dry). I’d guess that we’re not adding faster than we’re losing, though we could potentially change that ourselves in the years ahead.

[GordMay]

Most of Earth’s water did come from asteroids (and comets & meteorites), but some also came from the solar nebula (a cloud of gas and dust, left after the sun’s formation*1).

Research*, published in the Journal of Geophysical Research: Planets, on October 9, 2018. suggests that Earth’s water came from both rocky material, such as asteroids, and from the vast cloud of dust and gas remaining after the sun’s formation, called the solar nebula.
They present a first model for Earth's water origin, that quantifies contribution from the solar nebula*2, in addition to that from chondrites, the primary building blocks of Earth.

*1 Earth and the rest of the planets formed inside a nest of gas left over from the birth of the Sun. This material, known as the solar nebula, contained all the elements that built the planets, and the compositions varied with distance from the Sun. The region near the star was too warm for some material to coalesce as ices, which instead formed in the outer part of the solar system. Around Earth, hydrogen and other elements could stick around only as a gas. Because the nebula was short-lived, most scientists suspect that Earth didn’t have enough time to collect these gases before they escaped into space. That idea, along with the planet’s high D/H ratio, led many to believe that Earth’s water must have arrived after Earth had cooled.

*2 For every 100 molecules of Earth’s water, there are one or two coming from the solar nebula.

* “Origin of Earth's Water: Chondritic Inheritance Plus Nebular Ingassing and Storage of Hydrogen in the Core” ~ by Jun Wu et al.
➥ https://agupubs.onlinelibrary.wiley....9/2018JE005698

“Where did Earth's water come from?”
➥ https://astronomy.com/magazine/2019/...ater-come-from

[s/v Jedi]

I think today’s world starts looking more like Waterworld every day

[Pegu Club]

Originally Posted by anotherT34C

We’re also losing water as it escapes from the atmosphere (this is why Mars is apparently dry). I’d guess that we’re not adding faster than we’re losing, though we could potentially change that ourselves in the years ahead.

Valid point, we humans knowingly and unknowingly do indeed create change, both small and large.

[Singularity]

Hard to imagine that the moisture in our expiratory breath could ever amount to much, but given enough biomass it can create oceans. Without water, you can't have life...period. But once you get a smidgen of liquid water...if some amino acid legos vibrate together to create life...then the life starts producing more H2O (and CO2).

But life-produced CO2 isn't enough per se to create an atmosphere, and so it might help if you've got some volcanoes/vents outgassing; if/when these outgasses act to trap solar energy and expired H20 from microscopic life below...you get more ice melting, more melted water more microscopic life, more conversion of O2 to H20 by the life forms. Rinse and repeat for a few billions years=oceans. Maybe/probably.

Studies of earth rocks and asteroids finds similar compositions...in other words the cloud that coalesced as the earth likely had enough molecules on board to give us much/most of the water we have (i.e. not meteorite dependent).

[SaylorMade]

Originally Posted by Singularity

Hard to imagine that the moisture in our expiratory breath could ever amount to much, but given enough biomass it can create oceans. Without water, you can't have life...period. But once you get a smidgen of liquid water...if some amino acid legos vibrate together to create life...then the life starts producing more H2O (and CO2).

I am quite sure that water is not created that way.
It takes more action

https://science.howstuffworks.com/en...ture-water.htm

[GordMay]

Originally Posted by anotherT34C

We’re also losing water as it escapes from the atmosphere (this is why Mars is apparently dry). I’d guess that we’re not adding faster than we’re losing, though we could potentially change that ourselves in the years ahead.

The Earth is virtually a closed system, meaning that very little matter, including water, ever leaves, or enters the atmosphere; the water that was here billions of years ago, is still here now.

But, the Earth cleans and replenishes the water supply through the hydrologic cycle (water cycle).
Water doesn't escape, partly, because certain regions of the atmosphere are extremely cold. (at an altitude of 15 kilometers, for example, the temperature of the atmosphere is as low as -60° Celsius!) At this frigid temperature, water forms solid crystals, that fall back to Earth's surface.
Earth does lose hydrogen and helium, and cosmic rays will split water molecules, leading to a loss of an impressive amount of hydrogen, and as an indirect result a loss of water.

But ,this is loss practically irrelevant compared to the size of the oceans.
By one estimate, it will take about 30 billion years, at the current rate, and at the Sun's current luminosity, for Earth to lose just 1% of its oceans.
According to this model[*1], the tipping point should occur when mean solar flux reaches approximately 375 W/m2, with a surface temperature of around 70 °C (present-day flux is 341 W/m2), i.e. in approximately one billion years. The oceans will then start to boil and the greenhouse effect will increase until it enters a runaway state.

[*1] “Increased insolation threshold for runaway greenhouse processes on Earth-like planets” ~ by Jérémy Leconte et al.
➥ https://www.nature.com/articles/nature12827

[a64pilot]

Run the math, how many hundreds of thousands of comets does it take to equal a cu mile of water? Then there are hundreds of millions of cubic miles of water.
No, there is another explanation, I don’t know what it is, but I’m not believing the comet theory. Just too much water.

Water we expel is recycled water, we don’t create water

[GordMay]

Originally Posted by a64pilot

1. Run the math, how many hundreds of thousands of comets does it take ...?
2.Water we expel is recycled water, we don’t create water

1: Good question. I don't know; but although the population of comets and asteroids, passing through the inner solar system, is sparse today, they were much more abundant when the planets and sun were young.

2. Indeed.