PPS#94 | Blue Marble — Part 2: An Origin Story of Water and How This Liquid Came to Dominate Earth

Rebecca D'Souza
Sep 27, 2021
6 min read

Updated: Jan 18, 2022

Criteria: J | Water

The strength of water,

The life it gives,

Cannot be counted.

It cannot be measured.

No drops were counted

No river measured

Water simply flowed

And abundance was made and given.

The information I’ve collected (quite literally copy-pasted) and brought together to talk to you about today is, you know it, water. Our number one homie. Along with my commentary, we find out how Earth became home to a shapeless form that ebbs and flows. Water, a spectacular chemical combination.

Innumerable creation myths surround the stories of wild and subdued waters. Primal waters which still have the power to heal as it washes over you. The same water can also destroy; pushing everything away from its chosen path. With the inclusion of the primeval waters within creation stories[1] — Whether spiritual or not, water did initiate creation. H20 forms part of one of the most primordial constituents of the Big Bang:[2] Water is a part of Earth’s early history. Flowing water has had a long, tumultuous, and wonderful journey.[3] This is the living waters we drink, cook and clean with, bathe and swim in.

This post answers the question “Where did Earth’s water come from?” An origin story that led to the creation of seas, oceans, and plenty of water flowing across Earth’s surface. We’ll need to go back 3.8 billion years.

Dear Patient Reader,

Water covers about 71 percent of the Earth’s surface (a percentage close to and similar to the percentage of water found in the human body),[4] with 97 percent[5] of this water being found in the oceans. The remaining 3 percent is freshwater.[6] How much water is there on Earth? How much water does it hold? How much water flows through it? “If Earth was the size of a basketball, all of its water would fit into a ping pong ball. How much water is that? It’s roughly 326 million cubic miles (1.332 billion cubic kilometers), according to a 2010 study [that was carried out by] the U.S. Geological Survey (USGS).”[7]

Earth is estimated to be 4.54 billion years old (± about 50 million years),[8] and about 3.8 billion years back, water flowed along. But before that, a few facts about “how Earth’s freshwater is spread across the globe:

There is much more freshwater stored in the ground than there is in liquid form on the surface, according to the USGS.
70 percent of freshwater is locked in ice caps.
Less than 1 percent of the world’s freshwater is readily accessible.
6 countries (Brazil, Russia, Canada, Indonesia, China, and Colombia) have 50 percent of the world’s freshwater reserves (according to the USGS 2010 study).
One-third of the world’s population lives in “water-stressed” countries, defined as a country’s ratio of water consumption to water availability. Countries labeled as moderate to high stress consume 20 percent more water than their available supply.”[9]

Back to the 3.8 billion years ago origin story. The study of the origin of water on Earth is a part of research in the fields of planetary science, astronomy, and astrobiology.[10] Large bodies of water form part of Earth’s early history, and still do to this day. Which is one of the biggest reasons why Earth is habitable and hospitable for us humans, along with those we share our planet with. “Earth is unique amongst the rocky planets in the Solar System in that it is the only planet known to have oceans of liquid water on its surface. Liquid water, which is necessary for life as we know it, continues to exist on Earth’s surface because our beautiful blue planet is at a distance. This created a habitable zone; planet Earth being far enough from the Sun so that it does not lose its water to the runaway greenhouse effect. But not so far away that low temperatures cause all the water on the planet to freeze.”[11] Earth is pretty special, and different.

“Early Earth did not have an atmosphere making it easier for any liquid water droplets to be [literally] blasted off into space.”[12] That’s quite something. However, “we were nestled in the Solar System at just the right distance from the Sun for liquid water to exist. Any farther and water would freeze to ice. Any closer and temperatures would be too hot.”[13] There would be a lot of evaporation and steam. It would be one hell of a sauna. Being closer to the Sun, and with too hot temperatures, Earth would experience the runaway greenhouse effect. That would be similar to what’s happening on the scorching surface of Venus. “The distance Earth orbits the Sun is just right for water to remain a liquid.”[14] The ability for water to remain a liquid is a very important factor, and a very important part of our lives. Our not-too-cold, not-too-hot position in the so-called “Goldilocks zone” [which is the habitable zone; Earth’s distance from the Sun][15] is a pretty good thing.”[16] We got lucky.

The Earth stripped of its water (left). All of the Earth’s ocean water (middle) and freshwater (right). | David Gallo/WHOI

“It was long thought that Earth’s water did not originate from the planet’s region of the protoplanetary disk (the first phase of planet formation; where a large disk of gas and dust was swirling around the newly-formed Sun).[17] Instead, it was hypothesised that water and other volatiles must have been delivered to Earth (that sounds and well, is extraterrestrial) from the outer Solar System later in its history. On the other hand, recent research, however, indicates that hydrogen inside the Earth played a role in the formation of the ocean.[18] The two ideas are not mutually exclusive, as there is also evidence that water was delivered to Earth by impacts from icy planetesimals (the solid building blocks of rocky and giant planets)[19] similar in composition to asteroids in the outer edges of the asteroid belt.[20]

Confused and mind-boggled? Scientific jargon does that. Let’s break this down.

We are 3.8 billion years back and Earth is a young planet. Two well-accepted theories, ones I personally agree with, is that at the time icy comets or water-rich asteroids hit the newly formed, young Earth and watered it.[21] Following this theory, “models of the compositions of asteroids and comets suggest that they harboured enough ice to have delivered an amount of water equal to Earth’s oceans.”[22] That’s one. Now for theory two: When scientists went scouting across the world in search of Earth’s oldest rocks, they found that the rocks were made out of a lot of the primordial chemical substances that were coming together during that time in history; that of the inner Solar System which included Earth. These rocks had a composition that shared similarities to the bulk Solar System composition at the time. Making them viable candidates for the origin of water on Earth. And it turns out that those rocks contained lots of hydrogen. Perfect for contributing to the formation of water within and on Earth.

Another theory, a “2014 study by the Woods Hole Oceanographic Institution (WHOI) said that the Earth’s seas and oceans may have arrived much earlier on our planet than previously thought. Which pushes back the clock on the origin of Earth’s water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner Solar System were still forming.”[23]

Life as we know it is believed to have originated in the aqueous solutions of the world’s oceans. Water graciously offered hydration and moist surfaces that supported life in all its forms, shapes, and sizes, helping all living beings to grow, survive, and thrive. These were living organisms which became dependent on aqueous solutions, such as blood and digestive juices for their biological processes, like us. “Understanding how water arrived on Earth is a key part of understanding how and when life evolved here.”[24] Water, therefore, is a defining characteristic of our planet.

Although Earth’s systems, cycles, and hydrosphere are highly complex and complicated, as is the story behind the formation of water here on Earth, I hope this post sheds a little light on your understanding of our shared, majestic Blue Marble. All in all, whether comet impact or not, this all happened a very long time ago. An origin story and a liquid form that have dominated the surface of Earth as its mighty waters, ever since.

Have a good week ahead fellas. Ciao

P.S. If you’re interested in the theory that puts forward that water evolved on the planet instead of having external sources deliver water like a pelican with a baby swaddled in cloth, you can refer to the National Geographic article titled "Mystery of Earth’s Water Origin Solved”, linked below. Here’s an extract from the article:

“While the authors are not ruling out that some of the water that covers 70 percent of Earth today may have arrived later, their findings suggest that there was enough already here for life to have begun earlier than thought.” Good food for curious thinking.

"Mystery of Earth’s Water Origin Solved", an article by National Geographic

Another good read which I used for writing this post is an article by Scientific American titled "How Did Water Get on Earth?”, link below. It includes comparing the chemical make-up of cosmic objects to water on Earth, or Earth water if you want to make it sound fancy.

"How Did Water Get on Earth?” by Scientific American

P.P.S. Speaking of shedding light, next week’s post is titled “The light through the gaps”, which is about the warmth that touches our skin, sunlight.