Earth's Water Is Older Than the Sun

While theories about the origins of water are still up for debate, studies of the early solar sytem have shown water is older than the Sun itself. But how old is water and how did it get on Earth?

By Carl Engelking
Nov 20, 2023 2:00 PMMar 25, 2024 7:26 PM
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(Credit: maradonna 8888/Shutterstock)


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The sun, at 4.6 billion years old, predates all the other bodies in our solar system. But it turns out that much of the water we swim in and drink here on Earth is even older. Up to half the water now on Earth was inherited from an abundant supply of interstellar ice as our sun formed. That means our solar system’s moisture wasn’t the result of local conditions in the proto-planetary disk, but rather a regular feature of planetary formation — raising hopes that life could indeed exist elsewhere in the universe. 

Where Did Water on the Earth Come From?

Water through time: Ices from the parent molecular cloud are incorporated into planet-forming disks around young stars, and eventually into the planets themselves. (Credit: Bill Saxton, NSF/AUI/NRAO)

The origin of Earth's water has long been a subject of scientific inquiry and debate. Initially, scientists believed in the asteroid theory. However, recent studies suggest that Earth's water may have originated from the solar nebula. 

The Asteroid Theory

Many scientists believed that asteroids, which carried water in their minerals, brought water to Earth. This theory was supported by the idea that asteroids' heavy water content aligns more closely with Earth's current water ratio.

The Comet Theory

For a time, comets were also considered a possible source of Earth's water. This theory emerged when the European Giotto spacecraft observed Halley's Comet and its high heavy water content. However, further investigations showed that the heavy water ratios in most comets were too high compared to that on Earth, leading to doubts about their role in bringing water to our planet.

The Solar Nebula Theory

Astronomer Karen Meech and her colleagues focused on examining water in Earth's mantle. They studied samples from places like Baffin Island, where Earth's deep mantle is accessible. These studies involved analyzing the deuterium-to-hydrogen (D/H) ratios in the samples to understand the origin of Earth's water​. 

The samples showed about 25 percent less heavy water than normal water, suggesting that carbonaceous chondrites (a class of meteorites) might not be the primary source of Earth's water. These findings suggest that Earth's water could have originated from the solar nebula, the cloud of gas and dust from which the Sun and the planets formed​.

Read More: How Old Is the Oldest Stuff in the Solar System?

What Is the Age of Water?

The age of water on Earth is about 4.5 billion years old, as old as the Solar System itself. It started off in space, forming on tiny dust particles. 

As the Solar System was being formed, this water went through cycles of turning into gas and then back to ice, eventually becoming part of planets like Earth, as well as asteroids and comets. The fact that we find a special kind of water, known as heavy water, both on Earth and in these space objects, tells us that much of our water came from these early space processes.

Read More: What Are the Three Types of Water?

Is the Water on Earth Older Than the Sun?

Yes, water on Earth is older than the sun. In 2014, researchers determined the age of our solar system’s water by focusing on its ratio of hydrogen to deuterium, called “heavy hydrogen” because it has an extra neutron. Interstellar ice has a very high ratio of deuterium to hydrogen because it formed in very cold temperatures. Scientists already knew this from looking at the composition of comets and asteroids.

But, confounding the matter, deuterium levels in the solar system’s water have also been rising ever since the sun formed. So to determine if the sun alone could produce today’s levels of the isotope, researchers built a computer model that essentially wound back the clock to the beginning of the solar system and assumed no inherited deuterium.

However, the model system was incapable of producing deuterium to hydrogen ratios that were as high as those found in our solar system. Therefore, researchers estimate, 30 to 50 percent of our solar system’s water was already a part of the ancient molecular cloud that spawned the Sun and planets. 

Read More: 5 Interesting Facts About Water

Why Is Water Called the Universal Solvent?

Water is called the universal solvent because its unique molecular structure allows it to dissolve more substances than any other liquid. This is vital for transporting nutrients and chemicals in various environments. 

Water's polarity, with a positively charged hydrogen side and a negatively charged oxygen side, enables it to attract and break down different molecules, such as the sodium and chloride in salt. This capability makes water essential for life on Earth.

Read More: Why Are Humans So Drawn to Water?

The Implications of the Formation of Our Solar System

If our solar system’s formation was typical, cosmically speaking, then the findings imply that interstellar ices are in healthy supply for all up-and-coming planetary systems. And since all life we know of depends on water, that news improves the odds that other planetary systems have what it takes to support life.

Read More: The Quest for the Oldest Ice on Earth

A new twist, then, on the Rime of the Ancient Mariner: “Water, water everywhere, and every planet can have a drink.”

The Age and Origin of Water FAQ

How old is water on Earth?

Earth's water is around 4.5 billion years old, some of which predates the Sun. This ancient water originated from the molecular cloud that formed the Solar System.

How did water get on Earth?

Previously attributed to asteroids and comets, recent studies suggest Earth's water may have come from the solar nebula. This aligns with research on the deuterium-to-hydrogen ratio in Earth's mantle.

Is the Earth older than the Sun?

No, Earth is not older than the Sun. However, a significant portion of Earth's water, formed in interstellar space, is older than the Sun.

How old is water?

Water in the Solar System, including on Earth, is as old as the Solar System itself, around 4.5 billion years, with some of it predating the Sun.

How old is the Sun?

The Sun is about 4.5 billion years old. It formed from the same molecular cloud that contributed to Earth's ancient water.

Read More: Here's What Happens to the Solar System When the Sun Dies

This article was originally published on Sep 25, 2014 and has since been updated with new information from the Discover staff.

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