When you open the back of a fine watch...

When you open the back of a fine watch, you see layer upon layer of spinning wheels linked by interlocking cogs, screws and wires. Some of the cogs are so tiny they're barely visible. Size doesn't matter -- what's important is that the cogs fit together well so the wheels keep turning smoothly.

For centuries, scientists have thought of the Earth system as a series of cycles or interlocking wheels like the ones in a watch. It's a way to make sense of the movements of water and other essentials back and forth between the air and the land, ocean and soil or rock beneath them. In today's changing climate, some cycles are spinning faster or beginning to wobble. There's an urgent need to understand what is happening to the cogs that keep these cycles turning.

The minuscule fraction of Earth's water lodged just beneath the land surface is a tiny cog that links the water cycle to two other fundamental Earth cycles: energy and carbon. "That linkage is what makes these three gears turn with a certain harmony," said Dara Entekhabi of the Massachusetts Institute of Technology, Cambridge. Entekhabi is science team leader for NASA's Soil Moisture Active Passive mission, scheduled to launch Jan. 29. Developed and managed by NASA's Jet Propulsion Laboratory in Pasadena, California, SMAP will provide the most accurate information ever about this small but critical cog.

You may have learned about the water cycle in school: Water falls from the sky to the land when it rains or snows, and rises from the land back to the sky when it heats up and evaporates. Your teacher may not have mentioned that water vapor isn't the only thing that rises. The heat energy that turned liquid water into vapor also rises, cooling Earth's surface. In fact, evaporating soil moisture is the main way that land sheds the solar energy it receives every day and thus is a major player in the energy cycle. "It's the first process to kick in when the surface heats up, and it continues as long as there is moisture in the soil that can evaporate," Entekhabi said. Evaporation gets rid of nearly half of the solar energy that reaches land, keeping our planet's temperature comfortable.

If there's any moisture at all in soil, there's probably a plant growing there. That's why most evaporation from soil starts with a plant absorbing water through its roots. Plants need water for photosynthesis, their food-creating process. During photosynthesis they "sweat" -- or transpire -- water onto their leaves, where it evaporates.

Besides using water and energy, plants absorb carbon dioxide from the atmosphere during photosynthesis. Over land, this is virtually the only natural way for carbon to be removed from the atmosphere. Soil moisture keeps this vital carbon highway open by enabling plants to continue growing. "If a plant has access to water, it happily carries on with photosynthesis," Entekhabi said. "If not, the plant shuts down, and eventually it wilts and dies."

After SMAP launches, the new data it will provide are expected to help scientists answer some long-standing questions about what is likely to happen to these important Earth cycles in a changing climate. Entekhabi hopes to take advantage of the synergy available between SMAP and NASA's new Orbiting Carbon Observatory-2, which measures global carbon dioxide. "We have talked a lot with the OCO-2 scientists about how we can use simultaneous measurements to solve the puzzle of how plants respond to soil moisture and how the carbon cycle and the water cycle are linked," he said. "If we get that linkage right, we will reduce the uncertainty in future climate projections and know more about how terrestrial plants are going to act in the future."

SMAP will be the last of five NASA Earth science launches within 12 months. NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

Poza Azul in Cuatro Cienegas, Coahuila, Mexico

   

Poza Azul in Cuatro Cienegas, Coahuila, Mexico, is best known for its crystal clear turquoise water. The limestone landscape here has been eroded by acidic groundwater creating a system of caves and subterranean streams isolated from other water sources and rich with minerals that provide the range of Caribbean-like colors. Stromatolites abound in the warm water (93.2 F or 34 C) of this unique ecosystem that is home to several species of fish including Minckley's cichlids and Mexican tetraa. Photo taken on December 24, 2014

Early Homo sapiens, known from fossils found at Omo and Herto in Ethiopia

Early Homo sapiens, known from fossils found at Omo and Herto in Ethiopia, began making stone tools in the Nile Valley of Egypt some 150,000 years ago. Previous studies have traced their path out of Africa through Sinai to the Levant. New research reveals a second, more southerly route through Arabia, where modern human populations lingered for some 50,000 years before migrating north to the Levant. There they interbred with Neanderthals—and perhaps borrowed some of their tool-making techniques.

Stylistic and manufacturing similarities, the archaeologists say, connect the dots between tools made first in the Nile Valley of Egypt, then in the Arabian Peninsula, and, finally, in Israel. Those tools became progressively smaller and more sophisticated, similar to the evolution of mobile phones today.

"Archaeologists have always focused so much on 'out of Africa and into the Middle East' that we've missed an entire chapter of the human expansion in Arabia," says archaeologist Jeffrey Rose of the Ronin Institute, based in New Jersey, co-author of a new report published this month in Quartär.

Our species' birthplace was in Africa about 200,000 years ago, according to fossils from sites such as Omo and Herto Bouri in Ethiopia. While these fossils look modern, however, the populations they represent didn't begin to act fully modern until later.

A tool kit known as the Emiran, dated to almost 50,000 years ago, defines the transition between archaic and modern human behavior—at least as far as tool-making goes. But since the discovery of the first Emiran tools—points, blades, and scrapers found in a cave near the Sea of Galilee in Israel in 1951—archaeologists have puzzled over where this more advanced way of making tools began.

"The Emiran is the bridge technology," says Rose, who is also a National Geographic Emerging Explorer. "But where did these guys come from?"

Out of ... Arabia ?

Working with his former thesis adviser, archaeologist Anthony Marks of Southern Methodist University in Dallas, Rose studied all of the stone tools he could get his hands on in Arabia, northeastern Africa, and the Middle East.

In their new report, the pair says the evolution of stone tools in the region began in the Nile Valley of Egypt 150,000 to 130,000 years ago. These Nilotic hunter-gatherers in Egypt made Nubian tools by chipping away edges of a stone core in a systematic way to produce a single triangular point, which could be attached to a spear, for example.

While other researchers have proposed that the Egyptian Nubian toolmakers moved rapidly to the Middle East, where they invented the Emiran, Rose and Marks argue that they went to Arabia first—and that it was their Arabian descendants who would later develop the Emiran.

In their report, the researchers describe two different types of tool kits that appear to be offshoots of the Egyptian Nubian in Arabia and were developed 110,000 to 50,000 years ago: the Dhofar Nubian and the Mudayyan industries of the Nejd Plateau of Oman.

From the Dhofar Nubian to the Mudayyan, stone points get smaller and more elongated over time, becoming more similar to the Emiran tools, perhaps because the modern humans were using them as projectile points to hunt smaller, quick-moving animals as the climate got drier and finding food became more challenging. The people who made the Mudayyan tools in Oman were most likely hunting small animals like lizards and rodents, says Rose.

Picture of a Nubian Levallois core and point refit back together

A Nubian stone core (bottom right) and point (bottom left) are fit back together (top). Early modern humans in Egypt around produced such triangular points by chipping away the edges of a core. Later modern humans in the Middle East used a more efficient technique to make multiple points from a single core.

In their scenario, Rose and Marks suggest that the Arabian toolmakers pushed north into the Middle East when the climate changed dramatically in Arabia about 75,000 years ago. At that time, Arabia was beset by drought, which parched lakes and underground streams and converted grasslands into sand dunes.

By contrast, the climate began to grow wetter and more humid in the Middle East 60,000 years ago, drawing animals—and hunters—northward, according to the scenario proposed by Rose and Marks. There, modern humans made a major breakthrough: Instead of producing just one tool from a single stone by striking the core in one direction, from top to bottom, as their Nubian ancestors did, they learned how to strike many elongated blades from the top and the bottom of a single core, in succession—a telltale feature of the Emiran and subsequent Upper Paleolithic industries.

But in a surprising twist, the researchers also propose that the modern humans who made the Emiran were influenced by archaic people, possibly Neanderthals, who left behind fossils in Israel some 70,000 to 50,000 years ago, as well as more primitive tools, called Mousterian. The scientists say the Emiran tools are made in the same systematic manner as Egyptian Nubian tools, but closely resemble the local Mousterian tools.

The timing fits with genetic studies that suggest that modern humans interbred with Neanderthals when they arrived in the Middle East. A 55,000-year-old modern human skull from Manot Cave in Israel, reported last month, has provided new evidence that the moderns were there at the same time as Neanderthals.

Not everyone agrees that the Emiran hunter-gatherers' tool-making was influenced by their Neanderthal neighbors. The Emiran "has nothing to do with Neanderthals," says Harvard University archaeologist Ofer Bar-Yosef, who proposed a decade ago that the Emiran was made by Egyptian Nubians when they moved directly to the Middle East.

Regardless of who influenced the Emiran toolmakers, the long and winding path that led to modern tools may have taken a lengthy detour through Arabia.

"The Arabian region was not just the route to somewhere else, which it has often been considered in various dispersal scenarios," says paleoanthropologist Chris Stringer of the Natural History Museum in London. "It was at times a significant location in its own right for early modern humans and perhaps for Neanderthals too."

Volcano of Fire Erupts Under the Stars

 First, there was an unusual smell. Then there was a loud bang. But what appeared to the eye was the most amazing of all. While waiting near midnight to see a possible eruption of Volcán de Fuego (Volcano of Fire) in Guatemala last month, a ready camera captured this extraordinary image. Lava is seen running down the side of the volcano, while ash rises up, and glowing magma bubbles explode out of the caldera. Lights near the town of Escuintla can be seen in the background, one of several nearby towns that have witnessed several spectacular eruptions previously. High above, seemingly tranquil by comparison, are familiar stars from the night sky. Although the Volcán de Fuego usually undergoes low-level activity, when the next spectacular eruption will occur is unknown.

A Golden Gate Eclipse

 Shadows play on the water and in the sky in this panoramic view of the April 4 total lunar eclipse over San Francisco's Golden Gate Bridge. Just within planet Earth's shadow the Full Moon's disk is still easy to spot at its brief total phase. The urban night skyscape was composed to cover the wide range of brightness visible to the eye. The shortest total lunar eclipse of the century, this eclipse was also the third in a string of four consecutive total lunar eclipses, a series known as a tetrad. Coming in nearly six month intervals, the previous two were last April 15 and October 8. The next and final eclipse in the tetrad will be on September 28. This 2014-2015 tetrad is one of 8 total lunar eclipse tetrads in the 21st century.

Our solar system and search for new worlds

As NASA missions explore our solar system and search for new worlds, they are finding water in surprising places. Water is but one piece of our search for habitable planets and life beyond Earth, yet it links many seemingly unrelated worlds in surprising ways.

"NASA science activities have provided a wave of amazing findings related to water in recent years that inspire us to continue investigating our origins and the fascinating possibilities for other worlds, and life, in the universe," said Ellen Stofan, chief scientist for the agency. "In our lifetime, we may very well finally answer whether we are alone in the solar system and beyond."

The chemical elements in water, hydrogen and oxygen, are some of the most abundant elements in the universe. Astronomers see the signature of water in giant molecular clouds between the stars, in disks of material that represent newborn planetary systems, and in the atmospheres of giant planets orbiting other stars.

There are several worlds thought to possess liquid water beneath their surfaces, and many more that have water in the form of ice or vapor. Water is found in primitive bodies like comets and asteroids, and dwarf planets like Ceres. The atmospheres and interiors of the four giant planets -- Jupiter, Saturn, Uranus and Neptune -- are thought to contain enormous quantities of the wet stuff, and their moons and rings have substantial water ice.

Perhaps the most surprising water worlds are the five icy moons of Jupiter and Saturn that show strong evidence of oceans beneath their surfaces: Ganymede, Europa and Callisto at Jupiter, and Enceladus and Titan at Saturn.

Scientists using NASA's Hubble Space Telescope recently provided powerful evidence that Ganymede has a saltwater, sub-surface ocean, likely sandwiched between two layers of ice.

Europa and Enceladus are thought to have an ocean of liquid water beneath their surface in contact with mineral-rich rock, and may have the three ingredients needed for life as we know it: liquid water, essential chemical elements for biological processes, and sources of energy that could be used by living things. NASA's Cassini mission has revealed Enceladus as an active world of icy geysers. Recent research suggests it may have hydrothermal activity on its ocean floor, an environment potentially suitable for living organisms.

NASA spacecraft have also found signs of water in permanently shadowed craters on Mercury and our moon, which hold a record of icy impacts across the ages like cryogenic keepsakes.

While our solar system may seem drenched in some places, others seem to have lost large amounts of water.

On Mars, NASA spacecraft have found clear evidence that the Red Planet had water on its surface for long periods in the distant past. NASA's Curiosity Mars Rover discovered an ancient streambed that existed amidst conditions favorable for life as we know it.

More recently, NASA scientists using ground-based telescopes were able to estimate the amount of water Mars has lost over the eons. They concluded the planet once had enough liquid water to form an ocean occupying almost half of Mars' northern hemisphere, in some regions reaching depths greater than a mile (1.6 kilometers). But where did the water go?

It's clear some of it is in the Martian polar ice caps and below the surface. We also think much of Mars' early atmosphere was stripped away by the wind of charged particles that streams from the sun, causing the planet to dry out. NASA's MAVEN mission is hard at work following this lead from its orbit around Mars.

The story of how Mars dried out is intimately connected to how the Red Planet's atmosphere interacts with the solar wind. Data from the agency's solar missions -- including STEREO, Solar Dynamics Observatory and the planned Solar Probe Plus -- are vital to helping us better understand what happened.

Understanding the distribution of water in our solar system tells us a great deal about how the planets, moons, comets and other bodies formed 4.5 billion years ago from the disk of gas and dust that surrounded our sun. The space closer to the sun was hotter and drier than the space farther from the sun, which was cold enough for water to condense. The dividing line, called the "frost line," sat around Jupiter's present-day orbit. Even today, this is the approximate distance from the sun at which the ice on most comets begins to melt and become "active." Their brilliant spray releases water ice, vapor, dust and other chemicals, which are thought to form the bedrock of most worlds of the frigid outer solar system.

Scientists think it was too hot in the solar system's early days for water to condense into liquid or ice on the inner planets, so it had to be delivered -- possibly by comets and water-bearing asteroids. NASA's Dawn mission is currently studying Ceres, which is the largest body in the asteroid belt between Mars and Jupiter. Researchers think Ceres might have a water-rich composition similar to some of the bodies that brought water to the three rocky, inner planets, including Earth.

The amount of water in the giant planet Jupiter holds a critical missing piece to the puzzle of our solar system's formation. Jupiter was likely the first planet to form, and it contains most of the material that wasn't incorporated into the sun. The leading theories about its formation rest on the amount of water the planet soaked up. To help solve this mystery, NASA's Juno mission will measure this important quantity beginning in mid-2016.

Looking further afield, observing other planetary systems as they form is like getting a glimpse of our own solar system's baby pictures, and water is a big part of that story. For example, NASA's Spitzer Space Telescope has observed signs of a hail of water-rich comets raining down on a young solar system, much like the bombardment planets in our solar system endured in their youth.

With the study of exoplanets -- planets that orbit other stars -- we are closer than ever to finding out if other water-rich worlds like ours exist. In fact, our basic concept of what makes planets suitable for life is closely tied to water: Every star has a habitable zone, or a range of distances around it in which temperatures are neither too hot nor too cold for liquid water to exist. NASA's planet-hunting Kepler mission was designed with this in mind. Kepler looks for planets in the habitable zone around many types of stars.

Recently verifying its thousandth exoplanet, Kepler data confirm that the most common planet sizes are worlds just slightly larger than Earth. Astronomers think many of those worlds could be entirely covered by deep oceans. Kepler's successor, K2, continues to watch for dips in starlight to uncover new worlds.

The agency's upcoming TESS mission will search nearby, bright stars in the solar neighborhood for Earth- and super-Earth-sized exoplanets. Some of the planets TESS discovers may have water, and NASA's next great space observatory, the James Webb Space Telescope, will examine the atmospheres of those special worlds in great detail.

It's easy to forget that the story of Earth's water, from gentle rains to raging rivers, is intimately connected to the larger story of our solar system and beyond. But our water came from somewhere -- every world in our solar system got its water from the same shared source. So it's worth considering that the next glass of water you drink could easily have been part of a comet, or an ocean moon, or a long-vanished sea on the surface of Mars. And note that the night sky may be full of exoplanets formed by similar processes to our home world, where gentle waves wash against the shores of alien seas.

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Milky Way over Erupting Volcano

 The view was worth the trip. Battling high winds, cold temperatures, and low oxygen, the trek to near the top of the volcano Santa Maria in Guatemala -- while carrying sensitive camera equipment -- was lonely and difficult. Once set up, though, the camera captured this breathtaking vista during the early morning hours of February 28. Visible on the ground are six volcanoes of the Central America Volcanic Arc, including Fuego, the Volcano of Fire, which is seen erupting in the distance. Visible in the sky, in separate exposures taken a few minutes later, are many stars much further in the distance, as well as the central band of our Milky Way Galaxy situated horizontally overhead.