Unlike every other planet in our solar system, Earth’s surface is 70% liquid water. This is not only useful for life but also somewhat peculiar. Everything we know about how and when our planet formed indicates that Earth’s surface should be bone dry.
The story of our solar system’s formation begins with the collapse of a large cloud of dust and gas. The dense blob of gas at the center ignited to form the sun, which, as a young, unstable star, unleashed a fierce solar wind. Over time, this stream of charged particles pushed the remaining gas cloud farther and farther out, leaving only solid particles behind. These particles clumped together into rocks, planetesimals, and finally, the rocky planets of the inner solar system that we know today.
Here’s the problem: water, in the form of ice, couldn’t have been one of the solid particles that stuck around. The early inner solar system was far too hot for frozen water, and any water vapor would have been blasted away by the solar wind. So if Earth didn’t start off with water, how did we end up with such splendid oceans?
We know H2O wasn’t manufactured here over the eons, because natural processes like combustion, breathing, and photosynthesis create and destroy roughly equal amounts of water. Furthermore, the amounts in question are so minuscule that they can’t account for the abundance of water on the planet. Since Earth’s water was neither part of the original package nor manufactured here, it must have flown in from far away, on meteoroids or comets or other bodies originating in the outer solar system where they were far enough from the Sun for frozen water to survive.
Comets, being dirty iceballs, are a logical candidate for the source of our water, but were ruled out when we discovered that they are far richer in heavy hydrogen than Earth water. For every million hydrogen atoms in Earth water, about 150 are heavy ones, while typical comet water has twice that many. These mismatched chemical signatures suggest that Earth’s water could not have arrived on comets.
It turns out that the most likely source for Earth’s water is a type of meteorite called a carbonaceous chondrite. “Chondrite” is just the name given to the class of stony meteoroids that most commonly strike the Earth. But only the carbonaceous chondrites contain water – as well as lots of carbon, if you couldn’t tell from their name. They have water in them because they formed out beyond the sun’s “frost line”, and what’s more, their water has levels of heavy hydrogen similar to that of earth water, strongly suggesting that these earth-crashers are the source of our ice caps, clouds, rivers, and oceans.
And thus, the water that turned our planet into a blue marble came, quite literally, out of the blue.
Create a simple water cycle model using everyday materials. Use a plastic container, water, a small cup, and plastic wrap to simulate evaporation, condensation, and precipitation. Observe and document the changes over a few days. Discuss how this model helps us understand the movement of water on Earth.
Participate in a role-play activity where each student represents a different component of the early solar system (e.g., gas cloud, sun, planetesimals). Act out the process of solar system formation, focusing on how the solar wind affected the distribution of materials, including water.
Conduct an experiment to simulate the impact of meteorites on Earth. Use small rocks to represent meteorites and a sandbox to represent Earth’s surface. Add small amounts of water to the rocks and observe how water is transferred upon impact. Discuss how this relates to the theory of water arriving on Earth via carbonaceous chondrites.
Research and present on the concept of heavy hydrogen (deuterium) and its significance in identifying the source of Earth’s water. Create a chart comparing the deuterium levels in Earth water, comet water, and carbonaceous chondrites. Discuss why this evidence supports the theory of water arriving from carbonaceous chondrites.
Write a short story from the perspective of a water molecule traveling from the outer solar system to Earth. Include details about the molecule’s journey on a carbonaceous chondrite, its impact on Earth, and its eventual role in Earth’s water cycle. Share your story with the class and discuss the scientific concepts illustrated in your narrative.
earth’s – belonging to or associated with the planet Earth – The earth’s atmosphere is made up of various gases.
unique – being the only one of its kind; unlike anything else – The snowflake had a unique pattern that had never been seen before.
water – a transparent, odorless, tasteless liquid that is essential for all forms of life – The plants need water to grow and thrive.
composition – the nature of something’s ingredients or constituents; the way in which a whole or mixture is made up – The composition of the painting was a perfect blend of colors and shapes.
formation – the process of forming or being formed – The formation of a rainbow occurs when sunlight is refracted through raindrops.
solar system – the collection of eight planets and their moons in orbit around the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets – Our solar system includes planets like Earth, Mars, and Jupiter.
problem – a matter or situation regarded as unwelcome or harmful and needing to be dealt with and overcome – The math problem seemed difficult at first, but with practice, it became easier to solve.
source – a place, person, or thing from which something comes or can be obtained – The library is a great source of information for research papers.
comets – a celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing away from the sun – Halley’s Comet is one of the most famous comets that can be observed from Earth.
carbonaceous chondrites – a type of stony meteorite that contains organic compounds and water – Scientists study carbonaceous chondrites to learn more about the early solar system.
