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Scientists have known for years that water behaves weirdly.
Other liquids like alcohol and oil grow heavier as they’re compressed. But water becomes lighter — ice cubes float in a glass of water, after all. Other fluids grow denser as they cool. But, oddly, water is most dense at around 39 degrees Fahrenheit, or before it freezes.
Now scientists in Sweden have learned that water’s counterintuitive behavior stems from its uncanny ability to exist in two liquid states. Writing in the journal Science, they explained how sophisticated sensors helped them shed light on mysteries that researchers have spent more than a century trying to unravel.
They hope their work could eventually explain how water helped spark the creation of life.
“Water behaves very strangely compare to other liquids. We should be very grateful for it. Otherwise we probably wouldn’t exist,” Anders Nilsson, a study co-author and professor of chemical physics at Stockholm University, told Seeker. “Life couldn’t live without those properties because the bottom of the ocean would have frozen during the ice ages.”
Using mile-long, X-ray lasers in Japan and South Korea, Nilsson and his team were able to watch water molecules in millisecond-long clips as they transformed under increasingly colder temperatures.
It’s important to understand that ice freezes at 32 degrees Fahrenheit only when it contains impurities. Absolutely pure water, on the other hand, might not freeze despite sitting for years in subzero temperatures. In 2011, scientists discovered that water can remain a liquid until around minus 55 degrees Fahrenheit.
“Most people think water freezes at zero degrees Celsius but that is because you have crap in it,” said Nilsson.
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Nilsson’s team discovered that water will expand and contract as it grows colder, alternating between regular water and denser water that is around 20 percent heavier. Peculiarly, the alternating between less dense and more dense states intensifies as the temperature drops. Then, at around minus 47 Fahrenheit, it hits a 50-50 point where the fluctuations are equal. At colder temperatures, the fluctuations slow down again and it eventually starts becoming icy.
At those supercool temperatures, water separates like oil and water in a jar, said Nilsson. He suggested the denser water would look like milk.
At issue are the atomic bonds that comprise water molecules. Ice molecules have more space within their atomic structures than water molecules. That’s why they float in water. As temperatures cool, pure water molecules use that space to become more and less dense versions of themselves.
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The findings open up a new world for researchers, providing a potential origin to the bizarre behavior of water that previously was known to exist only as one of three states: a single liquid, vapor, and solid ice. Nilsson’s team is now figuring out how pressure might affect the two states of liquid water.
“The possibility to make new discoveries in a much-studied topic such as water is totally fascinating and a great inspiration,” Alexander Späh, a study co-author and Stockholm University doctoral student in chemical physics, said in a statement.
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