Water World Earth: Understanding our Wet Planet

Earth as a Planetary Science Topic

When I travel, I often pay close attention to the geological landmarks in the regions I visit. I do this because I’ve always been fascinated by rock formations, mountain ranges, and how features form. If you’ve never studied geology, it’s a great science to know. With a little practice, you can look at a landform and know the history of that region pretty quickly. It’s not so easy with water, particularly when I’m traveling via the ocean. However, this important substance plays a big role on our planet (and on other worlds, too).

Earth and Its Water

Planet Earth is a water world. During a recent talk to a general public audience, I explained how Earth’s oceans are thought to have formed, and how oceans appear to exist (or have existed) on other worlds in the solar system. I ended by talking a little bit about how Earth’s atmosphere, oceans, and land all interact with each other. These are topics familiar to planetary scientists, and of course, to climate and atmospheric sciences.

Earth’s systems interact in ways that we don’t always think about as we go about our day-to-day lives. For example, if it rains or snows, we all know that the water ends up in ponds, lakes, streams, and rivers. It makes its way to the oceans and exists in snow drifts and glaciers (in the case of snow). It also seeps underground and it can stay there for a long time. If you drink well water, you know that what you use comes from deep underground, basically from rocks. For many city dwellers, the idea that water can come from rocks is a complete surprise. I had a lengthy conversation with a woman on board the ship I just lectured aboard about this. After a talk about Mars, where I talked about the possibility of water underground on the Red Planet, she came up afterwards and asked about how it could exist in rocks. We had a great conversation about that.

The Role of Water for Life

Water is pretty important to life, so much so that it is one of the three main “requirements” that astrobiologists look for when they talk about life existing on other worlds, the others being warmth (energy), and organic material (food for the life to consume). All forms of life need to be wet in some way. We tend to focus on human needs for water, but every organism has some need of it to live and evolve and reproduce. That’s why so many people recognize the need for clean water to sustain life. It’s part of a healthy environment on any planet, but particularly on Earth.

Where Did the Oceans Come From?

On one of my most recent trips, I was crossing the Atlantic. On nearly every cruise trip where I am a science speaker,  someone asks me where the water came from. This time, I did a talk specifically about that. The truth is, however, scientists are still figuring out all the ways that Earth got its water. We used to say it came from comets. It’s possible that some of Earth’s water did come from specific families of comets, but it’s still an open question about how much of it did. Some comets did NOT contribute their water to early Earth, as we found out from the Rosetta mission when it studied Comet 67P/Churyumov-Gerasimenko. Comets of its type existed when Earth and the other planets were formed and being bombarded by solar system leftovers, but they didn’t contribute a lot to Earth’s water supply. Other families of comets may well have been suppliers, however.

Water and the Newborn Solar System

Infant Earth likely formed from water-rich planetesimals, and as this young world solidified and cooled, the water vapor from those protoplanetary objects condensed to form the first pools, rivers, lakes, and oceans. We also can’t ignore the contribution that water-rich asteroids and meteoroids made to Earth’s water budget. Early in Earth’s history, these objects slammed into the infant planet Earth (and possibly Venus and Mars), and contributed their water to the growing worlds.

If that delivery mechanism worked across the planets (and it’s pretty clear it did, due to the number of worlds (including moons and dwarf planets) that have (or had) water) then water is a ubiquitous part of the solar system. It holds the clues to a lot of things we still need to understand about the early solar system, and is an important part of the chemistry of the worlds where it exists.

Protecting Our Water

All that being said, water on Earth — particularly the clean variety — is a precious resource. It fuels us, but it also keeps the planet’s ecosystems in balance. Swamps and wetlands provide ways to filter water, bring oxygen to the atmosphere, and sustain a huge variety of organisms that we depend on (such as fish) for food and other products. Fresh water in rivers and aquifers provide drinking water for millions of people, and our bodies evolved to use that fresh water. Polluting it pollutes our bodies, and the life around us.

The oceans teem with life, with many forms not even yet cataloged (and some only recently being discovered). As we swept along the ocean, I kept thinking about all the life below us in that aquatic realm, and what it has meant to the planet. We know so little about that “world beneath the waves” even though we’ve learned a lot in recent years. We owe it to ourselves to protect and understand that world because, for all we know (and we know a lot), the world above the waves depends in many ways on the “aquasphere” of planet Earth.

Understanding our Planet

It’s important to study our planet (just as we do the other worlds of the solar system) as if we were exploring a new world (as we do in planetary science). Understanding its systems and features helps us understand other worlds. And, in a most interesting way, understanding THEM gives us new insights into the planet we call home. This goes way beyond politics and opinion; the fact is, we are still learning about this place we live on and that’s an important part of humanity’s education.

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