Science & Technology

How Did Earth Get All This Water?

Earth is a haven for water in our solar system. While only a small fraction of our water is drinkable, roughly 70 percent of our planet is covered in oceans, lakes, rivers, swamps, and other sources of our most precious liquid. Water is essential for life as we know it. What's frightening is that we know very little about how water got here in the first place.

Comet Delivery, or 'Born Wet'?

Earth was born from a cloud of dust and gas some 4.5 billion years ago, along with the rest of the solar system. Somewhere in its early life history, as it grew bigger from picking up nearby rocks and little worlds in its gravitational pull, it acquired water. How is the big question.

Some scientists suggest that comets delivered water to Earth. But that theory is ... complicated. Back in 2014, scientists discovered that a comet studied by the Rosetta mission — called Comet 67P/Churyumov–Gerasimenko — has a different type of water than what we have on Earth. So maybe some comets sent water to our planet, but certainly not all of them.

Or maybe, Earth was just "born" wet. Earth gradually accumulated its mass from picking up boulders nearby, and perhaps those boulders already had water in them. But if that's the case, how did we go from little bits of water in these boulders to the miles-deep oceans we see today on our planet?

Enter a New Idea

A new study suggests a solution to that second dilemma. It all has to do with the region where Earth was first formed. Luckily, our planet resides in a zone where water is not only possible, but common. The sunlight is warm enough to keep the water from freezing without being so hot that it evaporates away. A new model suggests our baby planet formed out of dust grains that contained water.

Over time, so the theory goes, the water-enhanced dust grains would stick together under the influence of gravity. Grains become pebbles, pebbles become boulders, and boulders become planetesimals — aka worlds that are a little smaller than planets. Eventually, planet Earth grew up from these water-rich origins.

"The new calculations also show that the small dust grains can collect enough water in 'only' a million years to explain the amount of water on Earth. A million years fits easily in the time it takes to form the larger boulders," read a statement from Netherlands Research School for Astronomy in Amsterdam.

Water Everywhere

While a million years is a long time, it's nothing compared to the 4.5-billion-year-old age of our solar system. The theory may also explain why we have water-rich worlds in other zones of the solar system.

That's right: As if water on Earth isn't awesome enough, we also have a Saturn moon called Enceladus that spurts water and life-friendly molecules, a Jupiter moon called Europa that has an ocean underneath a water ice crust, and plenty of other icy and watery worlds in our solar system alone. Why wonder where life is in the universe when we aren't even finished exploring the possibility of life in our own solar system?

The work comes from a pair of studies submitted to the journal Astronomy and Astrophysics. One study — which will be published there soon — was led by the University of Groningen's Martina D'Angelo. You can read the preprint (that is, a version that hasn't yet been peer-reviewed) publication here. The other study hasn't been accepted for publication yet; it's called "On Water Delivery in the Inner Solar Nebula" and was led by W.F. Thi of the Max Planck Institute for Extraterrestrial Physics in Germany.

Written by Elizabeth Howell September 14, 2018

Curiosity uses cookies to improve site performance, for analytics and for advertising. By continuing to use our site, you accept our use of cookies, our Privacy Policy and Terms of Use.