Origin of Earth’s Water

Quck answer

Scientists have long debated the origin of Earth’s water. One theory suggests that water was delivered by comets and asteroids during the planet’s early formation. Another theory proposes that water was present in the dust and gas cloud that formed the solar system, and was retained on Earth as it cooled. Recent research has provided evidence that supports both theories. Isotopic analysis of water on Earth and in comets has shown similarities, indicating a shared origin. Additionally, studies of meteorites have revealed the presence of water-bearing minerals. While the exact source of Earth’s water remains uncertain, it is likely a combination of these processes.


Playing in water on a hot summer day is a refreshing experience. Water is essential for our daily lives, from keeping ourselves and our clothes clean to quenching our thirst. But have you ever wondered where all this water came from? Is Earth the only planet with such abundance of water?

To understand the origin of water, we need to consider its composition. Everything in our world is made up of tiny building blocks called atoms. When atoms combine, they form molecules. Water, for instance, is made up of a molecule called dihydrogen oxide, which consists of two hydrogen atoms and one oxygen atom, commonly known as H2O.

So, when we ponder the source of water, we have to trace back the origin of hydrogen and oxygen. To do that, we must go back to the beginnings of our universe. Hydrogen has been present since the early stages of the universe. It is the simplest element. Oxygen, on the other hand, did not exist until much later, hundreds of millions of years later!

Inside the first stars, the temperature was extremely high, causing hydrogen to form other elements, including oxygen. Eventually, these stars died and exploded, spreading new elements across the universe. These elements then combined to form new substances, including water (H2O). Water molecules have been present since the formation of our solar system.

There were also water molecules within the Earth as it was being formed. However, does this account for the water we see on Earth today? Scientists are not entirely certain! There are several potential sources of water. Scientists propose that both of these explanations may be partially true. One theory suggests that water molecules deep within the Earth gradually rise to the surface over many years. In other words, the water that covers much of the Earth has been a part of the planet since its inception!

Another theory posits that water molecules arrived on Earth from other parts of space. During the early stages of our solar system, numerous asteroids and comets collided with Earth, bringing more water to our planet. It is likely that the water deep within the Earth, combined with the water from asteroids and comets, contributed to the abundance of water on Earth. In fact, over 70% of the Earth’s surface is covered by water!

Have you ever wondered about other planets? Earth is not the only planet that has a significant amount of water. Neptune and Uranus, for example, also have a lot of water. However, what makes Earth unique is its temperature. If we were closer to the sun and had a much hotter planet, all our water might evaporate. On the other hand, if we were farther away from the sun, our planet would be much colder, causing our water to freeze into ice like on Neptune and Uranus. Earth, with its mix of warm and cold temperatures, has water in the form of gas, liquid, and frozen.

The origins of water are truly fascinating to ponder! What do you think scientists will uncover next about our universe?

Give It a Try

Are you ready for more? Dive into these activities!

  • Only 1.2% of Earth’s water is readily available for drinking and other purposes. Are you using more than your fair share? Let’s find out! Try keeping a record of how much water you and your household use for several days, from washing dishes to flushing toilets. You can use this resource or find another one to help you keep track. Once you have data from several days, analyze it. What do the numbers reveal? Which daily activity consumes the most water? Share what you’ve learned with a friend or family member!
  • Now that you know how much water you use, let’s brainstorm ways to use less! With the assistance of an adult, conduct research online or at your local library to discover methods for conserving water. This website could be a good starting point. Create a poster using Canva or materials you have at home to educate others about what you’ve learned about water usage and conservation. Share your creation with friends and family!
  • Water is formed when hydrogen and oxygen atoms combine. It can be difficult to visualize something as tiny as an atom! Let’s use our imagination. Can you draw, paint, sculpt, or build a model of a hydrogen or oxygen atom? This website offers some ideas on how to do it, or you can come up with your own approach. See how many other atoms you can create! Don’t forget to share your creation with friends and family.

Sources of Wonder

  • https://www.britannica.com/dictionary (accessed 18 Apr., 2023)
  • https://www.usgs.gov/special-topics/water-science-school/science/where-earths-water (accessed 20 Mar. 2023)
  • https://scitechinstitute.org/earths-water-where-did-it-all-come-from/ (accessed 21 Mar. 2023)
  • https://www.youtube.com/watch?v=RwtO04EXgUE (accessed 21 Mar. 2023)
  • https://www.nasa.gov/feature/what-s-the-difference-between-asteroids-comets-and-meteors-we-asked-a-nasa-scientist-episode (accessed 21 Mar. 2023)
  • https://earthsky.org/space/water-in-uranus-and-neptune-rich-in-magnesium-ice-giants/ (accessed 21 Mar. 2023)

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