Ours is the blue planet, and the hallmark of life on Earth is water. When we look for life, we look for water. But where did this colorless, odorless liquid first come from? It turns out that the water in your bottle might be older than the sun. Recent discoveries in astrophysics suggest that water isn't native to Earth but instead was imported from the edges of our solar system as ice specks floating in a cosmic cloud long before our sun was set ablaze 4.6 billion years ago. Scientists think that half the water on Earth comes from interstellar gas predating the sun, and the rest was delivered as ice trapped in comets, and the Earth, unlike the moon, was able to hold onto much of the water. The ice within comets traps noble gases as well as a cocktail of other chemicals, such as silicates, carbons, and interplanetary dust, so these elements have likely always been present in the Earth's water. Comets may also have brought amino acids, the building blocks of biogenetic activity, to Earth.
We have all learned about and experienced the three states of water: Solid, liquid, and gas. Recently, scientists at the Oak Ridge National Lab (ORNL) have discovered that water exhibits a fourth state known as tunneling under extreme pressure and in small spaces. You'll never experience it as it only occurs in quantum mechanics and has no parallel in our everyday experience.
Water is also essential as a scale of our physical experiences. Most of the world, except Myanmar, Liberia, and the U.S., uses the metric system, and water is at the core of the relationship between volume and weight as 1 liter (volume) of water is 1 kg (mass).
The Celsius (Anders Celsius, 1701-1744 ) and Fahrenheit (Daniel Gabriel Fahrenheit, 1686-1736) temperature scales are based on freezing and boiling points of water. The Fahrenheit system uses 32° and 212°, respectively, as calibration points on the scale. In an arguably much more elegant solution, Celsius used 0° for the freezing point and 100° for the boiling point of water and divided the space between into 100 units, sometimes also called centigrades.
The water cycle, also known as the hydrologic cycle or the hydrological cycle, is the biogeochemical cycle that describes the continuous movement of water on, above, and below the surface of the Earth. The four stages of the water cycle are evaporation, condensation, precipitation, and collection. The water cycle has no starting point but let's start by looking at the ocean first. The sun provides the energy, and water evaporates as vapor into the air. The vapor rises into the air, where cooler temperatures cause it to condense into clouds. Cloud particles collide, grow, and fall out of the sky as precipitation in the form of rain, snow, or ice. The water falling from the sky lands in the ocean again. If the water falls on solid ground, the water is collected as runoff (rivers) or seeps into the ground (groundwater). Some groundwater finds openings in the geology and emerges as freshwater springs on their way to the ocean, where the whole process starts again.
It is hard to estimate the average length of one water cycle, as it depends on where the water is collected. It is thought that a drop of water spends about 3,000 years in the ocean before it evaporates. The journey continues quickly, with only about nine days on average in the atmosphere before precipitation. Snow and glaciers trap water for anywhere between 20 and 100 years, whereas water on the ice shelf can age to about 900,000 years. The vintage for groundwater can be anywhere from 200 to 300 years for shallow and up to 15,000 years for deep aquifers. You can do the math of how long this has been occurring on Earth, considering it is 4.5 billion years old. The water you're drinking has been in many things for the last couple of billion years, so use your imagination.
From the water that participates in the water cycle, 97% is in the ocean as saltwater. The remaining water is freshwater, with about 2% in the ice shelf and glaciers and 1% in groundwater and surface water like lakes and rivers.
In a recent discovery, a reservoir of water three times the volume of all the oceans has been found deep beneath the Earth's surface. The water is hidden inside a blue rock called ringwoodite that lies 400 kilometers underground in the layer of hot rock between the Earth's surface and its core. This discovery also leads to new ideas about where the water on our planet's oceans is coming from, challenging the notion of the cosmic ice theory. The water is all but inaccessible for us, especially if you think how deep 400 kilometers are. The International Space Station (ISS) is circling the Earth at a similar altitude, and we think that's pretty far in the sky.
It is well understood that we will never run out of water and that the water cycle will continue forever, or at least as long as the sun is ablaze. We have to worry about whether the water that we experience in the future will be potable and usable or polluted and contaminated. We will always have enough water, but the distribution will be a crucial factor. A drought in one area is as devastating as floods in another, even if the average stays consistent. Weather and geography will make a huge difference in what you experience. Will the water be where we need it? Will the water be drinkable and usable? Those are the challenges as we advance and far outside of the scope of this book. Still, conservation and preservation of water as a natural resource is the top priority of bottled water brands and their owners.
Water is a universal solvent, and to explain the concept, I love using the phrase "water is a soup" in my lectures and writings to challenge people to understand that water isn't H2O. Think about how we make soup. We have tasty chicken and some tasty vegetables, and we add water. After one hour, you have a tasteless chicken and bland vegetables but a great-tasting soup.
Rain, and other precipitation, are the origin of all water (if a circle can have an origin). But after rainwater falls, geological and meteorological factors influence the next step in the journey. When winter snowfall in the Alps melts in springtime, it flows into rivers and the underground water table. Springs at the base of the mountain then bubble forth with this relatively young water. But in other parts of the world, the ground may absorb falling rainwater quickly, and the water may not reach the surface again for another 10,000 years. Much of what we drink today is rainwater that fell hundreds or thousands of years ago. Water circulating in a deep spring, well, or artesian well is generally more protected from human and animal waste than surface water or water from a shallow aquifer. But deep-circulating water often has a higher mineral content because it interacts with rocks for more extended periods. Still, shallow-circulating water or even surface water may be of fine quality — environmental conditions make all the difference.
Shallow water and even rainwater are clean, safe, and delightful to drink from pristine and protected surroundings. Since the ultimate water source is always rain, let's look a little more closely at the places where the water emerges or is extracted.