This is a view of the Pacific Ocean, where different colors indicate the height of the tsunami in that area. The highest waves, in black, were probably more than eight feet tall. The orange and red areas indicate areas where the wave was closer to eight inches. Credit: NOAA

People in Japan face a catastrophe that has gone from terrible to tragic. The disaster began as an earthquake that launched a powerful ocean wave, called a tsunami, that caused destruction all along the coast. Those natural disasters damaged a cluster of nuclear reactors in Japan, leading to one of the worst nuclear disasters in recent years.

“My homeland has been struck by a tragedy of cataclysmic proportions. This has been one of the greatest natural disasters of modern times, the full extent of which is still becoming clear,” said Yukiya Amano, the director general of the International Atomic Energy Agency, in a press conference on March 14. “The events of the last few days are truly unprecedented.”

On the afternoon of Friday, March 11, an earthquake struck the floor of the Pacific Ocean 80 miles east of northern Japan. The U.S. Geological Survey reported the earthquake had a magnitude of 9.0, making it one of the most powerful in recent history. The magnitude of an earthquake is determined by measuring how strongly the Earth shook. People reported feeling the ground move all across the island country, both during the first quake itself and during hundreds of others that followed. Those later, smaller earthquakes are called aftershocks.

During the earthquake, the sea floor moved. That motion made the water go up and down and caused a tsunami, or a powerful ocean wave, that moved outward from the center of the earthquake site like the ripples that you see when a pebble drops in a pond. These ripples, though, were giant and spread out over the ocean.

Waves are how energy moves across the surface of the ocean, and when these waves struck Japan’s coast, they brought destruction. Within minutes, coastal towns flooded as unknown numbers of people were swept away with cars, boats and even buildings. Countries around the Pacific Ocean received tsunami warnings.

About 180 miles north of Tokyo, Japan’s capital city, two nuclear reactors were seriously damaged by the earthquake and tsunami. Although the reactors were equipped with safety devices intended to shut them down in case of an earthquake, the backup power supplies were also damaged by the quake and the tsunami. As a result, they failed.

The inside machinery of the reactors needs to be kept cool; if it’s not cool enough, a reactor could melt and possibly even destroy the protective metal vessel that encases the nuclear fuel. During a meltdown, radiation could be released into the air, threatening the health and safety of people nearby.

These nuclear reactors, part of a facility called Fukushima Daiichi, generate electricity for millions of people through a process called fission. During fission, a larger atom breaks into two or more smaller atoms. At most of the reactors at Fukushima Daiichi, atoms of an element called uranium-235 are the ones that break apart. Uranium-235 is natural on Earth, but it is unstable — which means it’s always ready to break apart. (The number 235 identifies how many protons and neutrons make up the nucleus, or heart, of a single atom.)

When an atom of uranium-235 fissions, it forms smaller atoms but also releases particles called neutrons. These particles can hit other atoms of uranium-235 and cause them to break apart — and then those newly split atoms release neutrons, which keep the reaction going and going. This is what occurs inside a nuclear reactor.

This reaction happens inside narrow rods that hold fuel pellets, which are immersed in water. As they undergo fission, the atoms inside the fuel rods produce heat. That heat will be transferred to water outside the reactor. As that water turns into steam, it is used to turns turbines that produce electricity.

The image on the left was taken by NASA’s Terra satellite on Feb. 26, 2011. The image on the right, which shows the extent of the flooding, was taken by NASA’s Aqua satellite on March 13, 2011, days after an earthquake and tsunami devastated Japan. The orange-red dot near Sendai is likely a large fire. Credit: NASA

Nuclear fission generates a lot of heat, so the nuclear reactors in which fission occurs need water to keep everything cool. At Fukushima Daiichi, which includes six reactors, water became the problem. According to the Nuclear and Industrial Safety Agency in Japan, the reactors lost power after the earthquake. That wasn’t a problem because backup generators started pumping water to remove heat building up inside the reactors. But when the tsunami struck, it took out those backup generators ― leaving the reactors dangerously hot. Then, another backup system, running on batteries, started. But it couldn’t keep up.

Explosions have seriously damaged other buildings associated with four of the reactors. A big and yet-unanswered question is whether it was the explosions or the excess heat in the reactor’s core that damaged the vessel that contains the fuel.

The core has become damaged. It appears to largely be holding the radioactive gases that have been developing. At times, however, reactor-safety teams have released small amounts of those radioactive gases to reduce the pressure in the vessel that holds the fuel.

Radiation levels around the reactors have become dangerous.

One reason is that old fuel rods from the six reactors at Fukushima Daiichi are stored near the reactors in pools of water. In many cases, those fuel rods are still quite hot. Circulating water is needed to cool these old fuel rods. But when the tsunami knocked out backup cooling to these pools, some lost much if not all of their water for a time. Under these conditions, radiation levels can increase enough to imperil the lives of workers. And on several occasions in the first week following the accident, many workers were sent home for their safety.

Some steam released from the reactors has also left the facility. Radiation from that steam has been detected in the countryside. Levels of radiation were not high, but because they could become high on short notice, people living within 20 kilometers of the reactor facility were told to evacuate. Those living between 20 and 30 kilometers of the plants were advised to stay indoors.

Even tinier amounts of radiation — levels almost too low to measure — have crossed the Pacific Ocean and been recorded in Washington State and California. As of March 21, these levels were too small to pose a risk to people living in the United States.

It will take months for Japanese officials to bring the reactors under control and for the country to dig out from the triple disaster that hit. Stay tuned.

POWER WORDS (adapted from the New Oxford American Dictionary)

Richter scale A way to measure the size of an earthquake, based on the measurements of seismographs. Destructive earthquakes typically have magnitudes of 5.5 or higher. A difference of one in the Richter scale represents an approximate 30-fold difference in magnitude.

seismograph A scientific instrument that measures the strength and duration of an earthquake.

tsunami A long, wide wave in the ocean caused by an earthquake or some other disturbance in the Earth.

fission The division or splitting of an atom into smaller atoms and into the particles that serve as building blocks of atoms.

radioactive Capable of producing ionizing radiation, which is powerful enough to remove electrons from other atoms.

uranium A gray, dense, radioactive element used in nuclear reactors.

Originally used to detect elusive particles from space called neutrinos, the four-story detector at the Sudbury Neutrino Observatory could be retrofitted to detect antinutrinos produced by natural radioactivity inside Earth.

Scientists have long known this strange fact: It’s easier to look deep into space than into the center of Earth. Light can pass through most of space, so the light from distant stars can easily be seen with the naked eye. But Earth is opaque, which means that light cannot pass through it.

If light cannot pass through it, then we cannot see what’s on the inside of our planet. So if we can’t use light to see inside our own planet, what can we use?

Recently, some scientists have been trying to use neutrinos — tiny particles smaller than an atom that zip through space. Neutrinos come from the sun or other distant stars, and astronomers have studied them for years. Now, a team of geoscientists — “geo” means Earth — think a kind of neutrino may have something to say about the Earth, too.

Not all neutrinos come from outer space. Special neutrinos called geoneutrinos are generated from within the Earth. (Remember that “geo” means Earth.) Most of these local neutrinos come from either the crust or the mantle. The crust is Earth’s outermost shell, what we stand on, and the mantle is five to 25 miles below the crust. Certain elements within the Earth can send off geoneutrinos when undergoing a process called radioactive decay.

During radioactive decay, a material loses some of its energy by sending out particles and radiation. An element that goes through this process is said to be radioactive, and radioactive elements occur naturally in the Earth. Some radioactive elements produce geoneutrinos.

After they are produced, geoneutrinos pass straight through the solid Earth without being absorbed or bouncing around. If they’re not stopped, they go straight into outer space — and keep going, and going and going. Geoscientists hope to catch a few of these particles on their way out, but it’s not going to be easy.

There are two big problems: There aren’t that many geoneutrinos, and they’re hard to find. To catch these elusive particles, scientists have designed special geoneutrino detectors. These strange-looking scientific instruments are giant, metal spheres buried deep underground.

In an abandoned mine in Canada, for example, scientists are preparing a geoneutrino detector that is four stories tall and more than a mile underground. The detector will be filled with a special liquid that flashes when a geoneutrino passes through. The liquid “produces a lot of light, and it’s very transparent,” says Mark Chen, the director of the project. When it’s up and running, probably in 2010, the detector will find only about 50 geoneutrinos per year. Other detectors are being planned all over Earth — one of them is even supposed to sit on the bottom of the ocean!

The geoscientists who study geoneutrinos hope that the particles will help answer an old question about the Earth. The interior of the Earth is blistering hot, but where does the heat come from? They know that part of the heat — maybe as much as 60 percent — comes from radioactive decay, but researchers want to know for sure. By measuring geoneutrinos, scientists hope to figure out how radioactive decay helps heat Earth.

Going Deeper:

Now, a team of scientists has found the oldest-known biological molecules inside some of those briny salt-water pockets. The team analyzed samples of salt mined deep underground in southeastern New Mexico. They found molecules of cellulose—the tough, fiber-like molecule that makes up plant cell walls. Algae and some bacteria also make cellulose. Because the molecule is made by living organisms, its presence in the salt deposit is evidence that some kind of ancient organism made the cellulose trapped inside.

Scientists found this ancient mat of tiny, threadlike cellulose fibers in 253-million-year-old salt deposits deep below the New Mexican desert. Each of the cellulose fibers, shown here through a microscope, measures between 5 and 16 nanometers (a human ha

Jack D. Griffith/University of North Carolina in Chapel Hill

To identify the cellulose molecules, the scientists removed material from inside the salt-water pockets. They placed the material in a hot solution of two chemicals, sodium hydroxide and sodium borohydride. This harsh solution dissolves all known biological materials except cellulose. The material didn’t dissolve, telling the scientists that the material in the salt deposits was most likely cellulose.

As an additional step, the researchers also mixed the material with a cellulose-digesting enzyme. This time, the material quickly dissolved. Taken together, these results give strong support to the scientists’ conclusion that the salt-water pockets contain cellulose.

The research team used radioactive dating to determine that the salt crystals—and the cellulose inside of them—formed more than 250 million years ago. In all that time, the crystals have hardly changed.

The findings tell the research team that ancient salt deposits like these might be ideal for preserving ancient molecules, which are signs of early life. A challenge to researchers looking for evidence of long-extinct living things is that the molecules that made up their bodies usually broke down because of exposure to sunlight, wind, water or other living things that digested them.

The salt-pocket cellulose tells another story: Buried deep below Earth’s surface, the encased cellulose molecules are protected from the sun’s harmful ultraviolet radiation and other harsh conditions. Such salt-water pockets might be ideal places to look for signs of long-gone life forms—both here on Earth and on other planets.

Scientists in a field called astrobiology are especially interested in these old cellulose molecules. Astrobiology is the study of life in the universe. Many astrobiologists focus on finding the best ways to search for life on other planets, aiming to answer questions about life in space—Does it exist now, and did it ever exist in the past?

It’s a good question, and one that’s hard to answer. After all, where would you start looking on Mars if you wanted to look for signs of life? As it turns out, both Mars and Jupiter’s moon Europa once had oceans—just like the New Mexico desert. Do they have similar salt deposits? No one knows for sure. But if planets and moons do, they might give scientists a good target to look for signs of past life.—Jennifer Cutraro

Power Words

From The American Heritage® Student Science Dictionary, The American Heritage® Children’s Science Dictionary, and other sources.

brine or briny Water containing large amounts of salt.

cellulose A carbohydrate that is the main component of the cell walls of plants. It is insoluble in water and is used to make paper, cellophane, textiles, explosives and other products.

digestion The process by which food is broken down into simple chemical compounds that can be absorbed and used in the body.

enzyme Any of the proteins produced in living cells that act as catalysts in the metabolic processes of an organism.

Europa The sixth moon of the planet Jupiter.

Jupiter The planet that is fifth in distance from the sun. Jupiter is the largest planet in the solar system and has the shortest day, lasting less than 10 hours.

Mars The planet that is fourth in distance from the sun. Mars is the third smallest planet in the solar system and is similar to Earth.

radioactive dating A technique for measuring the age of a material based on the spontaneous breakdown of a radioactive nucleus into a lighter nucleus.

ultraviolet radiation Electromagnetic radiation that has wavelengths shorter than those of visible light but longer than those of X-rays. Ultraviolet light is given off by the sun but is invisible.

Copyright © 2002, 2003 Houghton-Mifflin Company. All rights reserved. Used with permission.

Going Deeper:

Perkins, Sid. 2008. Salty Old Cellulose: Tiny Fibers Found in Ancient Halite Deposits. Science News 173(April 5):213. Available at http://www.sciencenews.org/articles/20080405/fob5.asp .

Cowen, Ron. 2007. A Crack at Llife. Science News 171(March 10):158. Available at http://www.sciencenews.org/articles/20070310/note12.asp .

Pegg, J.L. 2007. An Earthlike Planet. Science News for Kids (May 2). Available at http://www.sciencenewsforkids.org/articles/20070502/Note2.asp .

Travis, John. 1999. Prehistoric Bacteria Revived from Buried Salt. Science News 155(June 12):373. Available at http://www.sciencenews.org/pages/sn_arc99/6_12_99/fob3.htm .