When water flows over stones, it smooths them out and carries them in its path. Even when the steam has long since dried up, the gravel it leaves behind provides distinct evidence of the water’s former presence. And now the Curiosity rover has found tell-tale gravel embedded in the Martian bedrock, small stones rounded by water and too large for wind to have transported—rocky proof of water’s presence on the Red Planet. Although previous photos suggested that water once flowed on Mars, the rocks in outcrops like the one pictured here, dubbed “Hottah” after Canada’s Hottah Lake, are the most definitive evidence of water on Mars that we have ever found.
It’s easy to see how overwatering our crops would deplete the groundwater supply and cause land nearby to sink, but could it cause sea level to rise on a global scale? Yes, according to a model published in Nature Geosciences, that attributes 42% of the sea-level rise over the past half century to groundwater use.
Ninety percent of readily available freshwater is underground, and water used for drinking or crop irrigation must, of course, be brought above ground. That water then evaporates or flows into rivers, entering the water cycle and eventually the oceans, making them deeper.
A few days ago, we wrote about a remarkable graphic released by the USGS, showing all the water on Earth—freshwater, saltwater, water vapor, water in plants and animals; all of it—rolled into a sphere.
That sphere was only 860 miles in diameter, fitting comfortably between Salt Lake City and Topeka, Kansas, on a map. It was striking, especially considering that the water available for humans use in our daily lives is only a very small fraction of that; the vast majority of the Earth’s water is saltwater, and most of the freshwater is tied up in glaciers.
How big would a sphere of just the freshwater available to humans be? Reader Jay Kimball of 8020Vision, his interest piqued, went ahead and made such a graphic:
That sphere—the sphere representing the freshwater available to humans—has a diameter of just 170 miles. Head to his blog to see the math.
The cheapest and easiest way to disinfect water? Sunlight. Just leave a clear glass or plastic bottle out in the sun for six hours. SODIS, or solar water disinfection, is an age-old method touted by the World Health Organization for areas where access to clean water is limited. UV rays in the sunlight tear apart the microbes to make water safe. Drink up!
SODIS is quite effective, but scientists have found two hacks that make the technique even better. One problem is that the water may be cloudy from sediment, which can be fixed with a dash of salt. NPR’s Salt blog explains:
When you’re trudging through the pouring rain to the office, it seems like the Earth possesses an infinite amount of water, a not-insignificant amount of which is dripping down your collar. But when you see an image like this one, produced by the USGS, it hammers home the reality of the situation: the water’s all spread out in a very thin layer, like a millimeter of frosting on a cake. If you gathered all the world’s water—from oceans, lakes, groundwater, water vapor, everything—into a sphere, it would have a diameter of 860 miles. That’s the distance between Salt Lake City and Topeka, Kansas.
Flooding in Piazza San Marco, Venice
Venice is sinking, and the nearby Adriatic sea—like the global sea level—is rising. The city could, some estimates suggest, be underwater by the end of the century. Much of the trouble is due to Venice’s precarious, low-lying position in the middle of a lagoon, but human activity in the area has played a role in the city’s subsidence, as well. As Scott K. Johnson explains at Ars Technica:
The pumping of shallow groundwater in the mid-1900s also contributed to the problem. Water in the pores between grains of sediment provides pressure that bears some of the load. When pore pressure decreases, or water is removed completely, grains can be packed together more tightly by collapsing the pore spaces. As sediment is compacted, the land surface drops. While the effect was small (less than 15cm), Venice doesn’t have much wiggle room.
What’s the News: Astronomers have known for many years that Saturn’s moon Titan sports lakes of liquid methane. And in the past couple years, scientists have suggested that it also has an underground ocean composed of water and ammonia. Now, based on past observations by NASA’s Cassini spacecraft, astronomers are saying that Titan’s rotation indeed points to an underground sea—and where there’s water, there may also be life. “Our analysis strengthens the possibility that Titan has a subsurface ocean, but it does not prove it undoubtedly,” researcher Rose-Marie Baland told Astrobiology Magazine. “So there is still work to do.”
What’s the News: If you were to bring a glass of water to Mars, the liquid would instantly boil because the Red Planet’s carbon dioxide atmosphere is so thin: The vapor pressure of the water easily surpasses the weak atmospheric pressure, sending water molecules flying off quickly into the atmosphere. However, ancient shorelines and river-like features indicate that Mars had a watery past, leading researchers to wonder what happened to Mars’ once-thicker atmosphere. Now, data from the Mars Reconnaissance Orbiter has uncovered a massive deposit of solid CO2 at the south pole that could double the planet’s atmospheric pressure if it were released as gas. “If you double the amount of CO2 in the atmosphere, it’s quite possible that you could have liquid water,” planetary scientist Philip James of the Space Science Institute in Boulder told Scientific American. “People have suggested that this could happen, and now it looks like it could be possible.”
What’s the News: Scientists have developed a new process that condenses diesel fuel exhaust into water. If implemented on the battlefield, it would allow soldiers to produce drinkable water from burnt fuel in tanks, generators, and Humvees, freeing them from carrying quite so many heavy water-filled containers. “Theoretically, one gallon of diesel should produce one gallon of water,” project leader Melanie Debusk told MSNBC.
What’s the News: This week, scientists say that they’ve passed a chemistry milestone by creating the world’s first practical photosynthesis device. The playing-card-sized photosynthetic gadget uses sunlight to split water molecules into oxygen and hydrogen, which can then be used to produce energy, and is reputedly 10 times more efficient than a natural leaf. Researchers say they expect it to revolutionize power storage, especially in remote areas that don’t currently have electricity. “A practical artificial leaf has been one of the Holy Grails of science for decades,” says lead researcher Daniel Nocera, who’s presenting this research at the National Meeting of the American Chemical Society this week.
How the Heck:
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Reference: Daniel Nocera et al. 241st National Meeting of the American Chemical Society. March 27-31, 2011 Anaheim, California, USA
Image: Wikimedia Commons / Daniel Schwen