The Origin Of Earth’s Water

My last post was about waves.  This one is about the water that makes waves.  The very water that gives us life.

And, more importantly, the water that floats our boat.  

🙂

Photo source:  Sciencemag.org

The BIG Question

Did you ever stop to wonder where it all came from?  Our vast oceans, seas, rivers, and hundreds of thousands of lakes?  That's the water we see.  But you know, there is also a of water on Earth we don't see.  

So why is it we have so much?  After all, water makes up 70% of Earth's surface.  And though water only makes up 0.023% of Earth's mass, that's still a lot of water.  

In fact, 1.35 x 10¹⁸ metric tonnes of it.  That's 326 quintillion gallons (326,000,000,000,000,000,000).  Give or take a gallon or two.

If you took all of Earth's water and compressed it into a single drop, this is how big it would look.  The truth is, that drop would only have a diameter of 860 miles. That's it.  

This image shows the proportional relationship between Earth's land, oceans, and freshwater.  

Image source:  Public Domain.  

The truth is, no one really knows where all our water came from.  There are theories of course, but they change and evolve over time.  None is as incontrovertible as, say, Evolution.

 
For many years, the leading theory was that most of Earth's water came from meteorites,  particularly a meteorite called a “Carbonaceous Chondrite Meteorite.”  This type of meteorite contains ice from an area of the solar system called the “Frost Line.”  The Frost Line is located on the outer edge of what is called the "Goldilocks Zone" (an area where temperatures are not too hot or too cold for liquid water to exist), between 2.7 and 3.1 AU's.  (One AU, or Astronomical Unit, is the distance from Earth to the Sun.)  

But just last year, in 2020, there was an astonishing discovery that really got scientists buzzing.  The new theory, based on geologic findings, is that most of our water was always here, just not in condensed, liquid form.  

But before we get to that let's start with the history of water.



History Of Water

In the Hadean and Archean eras, a huge astroid impact occurred, ejecting a large volume of material at high velocity into space. The particles, chunks, and boulders both small and large were pulled together by gravity and formed a very large object in the sky… our Moon.  But much of the ejected mass from that asteroid was still trapped inside earth's atmosphere, including a large volume of carbon dioxide due to the impact.  That CO2 exerted so much atmospheric pressure, liquid water formed, even though earth's surface temperature was still hot, at 446°F.  This contributed some of our water.

Where's the proof?  There is evidence that liquid water existed 3.8 billion years ago from a discovery in Quebec, Canada, where mineralogists found pillow basalt -- a type of rock made during underwater volcanic eruptions.  Another study showed that these rocks were even older -- 4.28 billion years.  Those are some old rocks! 

But it's not possible that all our water came from one giant asteroid impact.  So where did the rest of it come from?

Here is a cool video of an underwater volcanic eruption forming igneous rocks very similar to pillow basalt.  

Carbonaceous Chondrite Meteorites

Carbonaceous Chondrites contains water.  Not just a little bit.  Water can amount to 22% of their mass.  That's astonishing!

The largest Carbonaceous Chondrite meteorite we know of is called the Allende meteorite.  It was a bolide, which means it burst before reaching our planet's surface.  Since it exploded over Chihuahua, Mexico at 1:05 p.m. on September 8, 1969, I'd have called it the "Exploding Chihuahua." :)

Many shards were recovered totaling around 2 tons.  Of that 2 tons, if we assume they contained 22% water, I calculated that the amount of water which entered our atmosphere was 880 lbs.  (2 tons = 4000 pounds.  4000 x 0.22 = 880 pounds.)  While it may not be possible to get blood from a stone, it turns out you can get a lot of water from some!

[One amazing fact about Carbonaceous Chondrite meteorites is that they have amino acids inside them.  One of them was found to contain 52 amino acids.  This is the only type of meteor known to contain any amino acids at all.  And this is important, because amino acids are building blocks for every form of life known to man.]

So here's the part where I get to the old theory...  

Until recently, these very meteorites were thought to be the predominate source of Earth's water.  But doesn't that seem like a stretch?  I mean, 326 quintillion gallons flying into earth one meteorite at a time?  That'd be a lot of Chihuahuas!  While that may be where Chihuahuas came from, we need a better theory for our water.

                                                             

The New Theory

The new prevailing theory about the origin of water on earth is that most of it didn't come here in through astroids or meteorites containing ice.  It was actually here the whole time.

This new theory has already been widely accepted in the scientific community because the evidence in support of it is overwhelming.

It turns out that water from astroids is "heavier" than the majority of water found on earth.  

But wait...  What is heavier water?  Doesn't all water weigh the same?

Actually no.  The water found on meteorites is heavier because of a special type of Hydrogen atom in its H2O compound.  That type of Hydrogen is called "Deuterium."  I won't get too technical here, but Deuterium or "heavy Hydrogen" is a Hydrogen atom that has a proton and a neutron in its nucleus, whereas normal Hydrogen atoms, called "Protium," have only a proton.

In other words, if all or most of our water came from Carbonaceous Chondrites, it would contain this heavier Hydrogen atom.  

But it doesn't.  

So, out with the old [theory] and in with the new!

Here is a very interesting website about the isotopes of hydrogen.  It's not too complex.

https://courses.lumenlearning.com/introchem/chapter/isotopes-of-hydrogen/

__________

Where Is All Our Water?

The lion's share of Earth's water, 97%, is in our oceans.  Beyond that, and that of our lakes, rivers, streams, puddles, and dewdrops, there is a lot more water on earth.  But where? 

Ice Caps

Ice caps account for roughly 79% of the world's fresh water supply.  Though, of course that water is inaccessible for our use.

Groundwater

Groundwater, as the word suggests, means water that is underground.  There's more of it than you'd think.  Groundwater makes up approximately 20% of all of Earth's freshwater.  Some of that water is gathered in underground aquifers, which we pump from wells to provide freshwater to our towns and cities.  There is a lot of discussion about how long our water `supply will last.  Some areas are using far more than is being replenished by the water cycle.  The Central Valley of California, for instance, is pumping water that took tens of thousands of years to accumulate from the last ice age.  This level of consumption is far from sustainable.  Our country's coming freshwater shortages will begin on a regional level.  As certain regions run lower on their water supply, they will demand water from other regions (such as the Great Lakes).  The battleground for water resources will be a bitter political and legal one.  

Because groundwater is unseen, we don't notice it.  I think groundwater deserves a little more respect.  Did you know water vapor coming from evaporated groundwater makes up between 70% and 95% of all gasses in a volcanic eruption?  

While ash and sulfur dioxide and hydrogen sulfide get all the credit, it's the groundwater that's putting on the show!

__________

Water In Our Solar System

The word ocean means an expanse of liquid water.

Are there other oceans out there in the "ocean" of our solar system? 

Yes!  According to Wikipedia, there are 11 different surface oceans in our solar system alone.  And 6 global sub-surface oceans under their ice.  Here are some of them.  You can see that Earth's oceans compared to Titan's and Ganymede's are tiny.  And hey, those aren't even on planets.  They're on moons!

Image source:  NASA / JPL

Image source:  Planetary.org

Ganymede's composition.  That's one watery moon!  

Image source:  Time magazine.

So, as you can see, there's lots of water in our solar system.  

As far as we know though, there aren't any marinas or anchorages out there.  😁

Water Beyond Our Solar System

A quasar or "Quasi-Stellar Object" (QSO) is a very bright "Active Galactic Nucleus" (AGN) which means it's a huge disk of matter (called an "Accretion Disk") glowing with energy around a black hole.  (Those are some fancy science words.) 

Artist's illustration of a quasar.  

Image source:  Earthsky.org.

Ok, that's great, but why are we taking about Quasars when this post is about the origin of our water? 

Well, in 2011 two teams of astronomers discovered the farthest and largest water reservoir ever known to science.  It is in quasar APM 08279+5255 (who names these things anyway?), 12 billion light years away, and contains 140 trillion times the volume of water found on Earth.  

Here's an actual photo of MG J0414+0534 by Hubble.  It is a water-bearing quasar 11 billion light years from Earth.

Image source:  physics.org

When you consider the whole observable universe has a radius of 46.5 billion light years, and this is just one quasar of the estimated 750,000 quasars known to us, and that those are just the ones we can see thus far from Earth, you get the impression that our universe contains massive amounts of water.

🤯 

 

So, no, we are absolutely not the only planet with water, and that makes sense because... 

...drum roll please...

...water happens to be the second most abundant compound in the universe.

__________

What Is Water?

Nearly every molecule of water on earth is billions of years old.  (An exception to this is water formed as a byproduct of fuel cells.)  

Here's something about water that came as a surprise to me.  Did you know water is described as "sticky?"  It's true.  Water likes to stick to itself so much that water droplets will pull up against gravity to stick to each other.  I find it funny that water is sticky.  Think about it.  When we get sticky fingers, don't we use water to wash our hands?  We do.  And when we do, we are actually using sticky to clean sticky.  Sort of like fighting fire with fire I suppose.  

Water has another uncommon property.  Water is the only substance known to man that expands when it freezes.  In fact, that is why ice cubes float.  They are less dense (more space between the molecules) than the water they are floating in.  By the way, this really helped life evolve in our oceans.  The ice on top insulated the water underneath, making it warmer, and blocking some of the harsh radiation that damages DNA.  

DNA

Photo source:  Nebula.org.

Here's another fun fact about water.  Water on the bottom can actually freeze faster than water at the surface.  Because heat rises, water on the bottom will be cooler than that above it.  And because that cooler water on the bottom is denser, there will be no convection to mix it with the warmer water above.  No convection means no friction to "share the warmth."  As a result, water on the bottom will start freezing first.  

And here's one final interesting fact about Earth's water.  We've been losing it over time through two naturally occurring processes.

1.  Atmospheric escape. This is where water vapor drifts high into the atmosphere and is eventually just lost into space.

2.  Photolysis (also known as Photodissociation or Photodecomposition).  This is where water molecules in our atmosphere are broken apart by photons in sunlight. 

How much have we lost?  Around 1/4 of our oceans' original mass.  It'd take a lot of "Exploding Chihuahuas" to replace all that! 

__________

Earth's water has been in amazing places.  Pour yourself a glass and think about it.  Some of that water could have been in Challenger Deep (the deepest point in Earth's hydrosphere, 35,800 feet below sea level), or within the ash plume of a volcanic eruption, or way up, even 1,000 miles high in the atmosphere, or inside a dinosaur, or frozen on the windswept peaks of Mount Everest.  And yes, even inside a pelican or two 30 million years ago.  :)

__________

So that's my post about water.  My dad helped me a lot less with this one, even though he assigned the subject.  I'm pretty proud of it, and learned a lot researching it, including many things about the biological roles water plays in our lives which I might save for a future post.

I always like to end my posts with something fun or funny.  So here you go.