In Memoriam. . . David Wynn-Williams 1946 - 200
The astrobiology community mourns the sudden, tragic loss of David Wynn-Williams, who was killed on the evening of Sunday, March 24, 2002, in a traffic accident while jogging near his home in Cambridge.
David's passion, enthusiasm, commitment, energy, and scholarship touched many of us directly, and many more indirectly. Our thoughts are with his family.
We feel fortunate to have captured David on video recently, describing the work he so loved in Antarctica. To view the video, click on the appropriate bandwidth link below.
Letter from NAI Director, Baruch S. Blumberg
Featured Profile: David Wynn-Williams
The Multi-Tasking Pigments of Antarctica
By Holly Davis and Daniella Scalice
Imagine hot chocolate with breakfast, sliding on heavy-duty sun glasses, skiing down a perfect white slope, and watching your breath form little clouds in the subzero temperatures as you swish past fascinating rock formations. Sound good? Well, far from being a winter ski weekend in the luxurious Swiss Alps, these events are part of a typical day in the field for microbiologist David Wynn-Williams of the British Antarctic Survey. His research, funded in part by the NASA Astrobiology Institute, while focussing on one of life's smallest creatures, addresses one of humankind's biggest questions: "Did life evolve on Mars?"
Step one: becoming photosynthetic…
Dr. Wynn-Williams studies microscopic bacteria called cyanobacteria living in one of Earth's harshest environments, the dry deserts of Antarctica's inland valleys. The cyanobacteria, or blue-green algae, Wynn-Williams studies live not only on the surface of the ground, but inside the rocks and soil as well. They can penetrate up to 8 mm into hard rock, about the thickness of a CD case. The sandstone in which they grow allows enough light through so the cyanobacteria can do their thing: photosynthesize. Using special molecules inside their cells, some of which are called pigments, they harvest light energy from the sun and carbon dioxide from the air and turn them into sugars - food, or energy - that they can "eat" in order to live and grow. This food, which they incredibly produce within themselves through the process of photosynthesis, is their sole source of sustenance.
"Photo" = light, synthesis = create, "photosynthesis" = to create using light.
Indeed, the cyanobacteria Dr. Wynn-Williams studies in the Antarctic are photosynthetic, but he believes they evolved from a similar, more primitive ancestor who had never seen the sun. It is believed that life may have originated underwater in a sea-floor hydrothermal vent. situation, and those life forms, probably bacterial, did not have the ability to carry out photosynthesis. That is, they did not use light from the sun as their source of energy. Rather, they used the energy released when heavy elements such as iron and magnesium (abundant in hydrothermal vent fluid) undergo chemical reactions and change form. The theory is that life was not originally photosynthetic because the conditions under which life arose did not involve direct sunlight. Life became photosynthetic. Wynn-Williams believes the same type of evolution could have occurred on Mars.
As the story goes, life eventually rose from the bottom of the ocean to the surface, and learned how to use pigment molecules to harness the energy of the sun to make food. But the sun's energy, while indispensable for survival, can also be harmful to microbes, and they need to protect themselves. As it turns out, the pigments used by the Antarctic cyanobacteria for photosynthesis have an additional, crucial role. During the winter months, the hole in Earth's protective stratospheric ozone layer naturally widens, flooding the continent with ultraviolet radiation from the sun. Such UV radiation would give us a sunburn, so we would simply put on sunscreen to protect ourselves. But what's a cyanobacterium to do? Use its pigments, of course.
Nature's Sunscreen: Pigments
In order to live in such an inhospitable environment, the cyanobacteria employ all their resources, including their pigment molecules, for survival. These pigment molecules, called hopanoids, not only function to harvest light energy for photosynthesis, they also serve as a shield to protect the organism's vulnerable DNA from the damaging, mutagenic UV rays of the sun. Finally, the pigments also help the bacteria expel excess energy that builds up within its cells.
But the pigment story goes on. Unlike mammals, who have skeletons made of hard bone which can last for eons, cyanobacteria and other microorganisms are made simply of fluid contained by a membrane - imagine a tiny soap bubble filled with water. So when they die, they don't leave obvious signs or markers telling us where they've been, like dinosaurs leave their skeletons behind for us to dig up. But what they do leave behind are their pigment molecules, lying there in the rock and soil for anyone to see. Anyone that is, who knows how to look.
Inspector Gadget, Take Note: Introducing the Mini Raman Spectrometer
Dr. Wynn-Williams, it just so happens, has an instrument called a Raman spectrometer which can detect these fossilized pigments left behind by microorganisms which lived in Antarctica 3 billion years ago, about two thirds as long as the Earth itself has existed. Wynn-Williams determines which fossilized pigments are indicative of which ancient cyanobacteria using his mini Raman spectrometer that weighs only a kilogram (2.2 pounds) and fits easily in a backpack. The Raman spectrometer consists of a laser beam which is shone into rock or soil to determine which molecules and chemicals are there. The spectrometer measures both organic, or carbon-containing, and inorganic, or non-carbon-containing molecules. This allows scientists to determine the unique fingerprint of each pigment in the cyanobacteria, as well as the composition of the minerals in the rocks or soil in which they live.
The laser in the spectrometer produces light of one wavelength. In the latest version it emits light with a wavelength of 1064 nanometers, which is in the near infrared range just below the threshold of what our eyes can see. When scientists shine the laser into a sample, most of the light comes back at the same wavelength, but some of it is scattered by the vibrations of the molecules.
Vibrating Molecules + Light = Spectra
Everything on this planet that is above absolute zero temperature (-273 degrees Celsius) is vibrating at some frequency. How a molecule is constructed determines how it vibrates. For simple, inorganic molecules, the type of vibration depends on the bonds linking the atoms. For larger, organic molecules, the vibrations depend on structural features such as rings, double bonds, and side chains.
"These vibrations change the wavelength of the laser light ever so slightly," Wynn-Williams explains. "It's a bit like what you might have heard of as the Doppler shift." If a police car is going past you, the sound of its siren seems stronger as the car approaches, and softer as it goes away. With light, the wavelength is slightly shorter when parts of a molecule vibrate toward the laser and slightly longer when the molecule's parts are vibrating away.
When the detector head reads all the light that has been scattered back from the vibrating molecules, the spectrometer reports a dominant signal at the laser's original wavelength, which is used as a reference point. On either side of that point, scientists see some wavelengths that are shorter and some that are longer. This range of wavelengths comprises the spectrum, hence the name "spectrometer." In other words, the spectrum is made up of all the deviations from the original wavelength of light.
Dr. Wynn-Williams has been taking pure samples, measuring their spectra, and cataloging them to create a library of known organisms and pigments. When he goes out into the field and takes spectra from an unknown sample, he can reference his library of spectra to determine the molecules present in the unknown. For example, the spectra produced from a lichen, which is a combination of algae and fungi, consists of one mountainous peak with lots of little peaks on the shoulder of the mountain. Using his catalog of spectra, he can recognize the little peaks on the shoulder of the mountain and say with certainty which types of molecules are in a lichen.
From Antarctica to Mars
In Antarctica, Wynn-Williams is using the Raman spectrometer to identify pigments belonging to microorganisms that existed three billion years ago. "We can shine the laser light into ancient [dead] microbes as fossils, or into modern [living] ones and we can recognize the biomolecules they contain, and so we could potentially put one of these things on Mars," Wynn-Williams says. Successful use of the spectrometer doesn't require that the sample be prepared in any special way, or the microbes be extracted from the rock in which they live. This makes it an ideal tool for remote exploration on Mars.
In order to find either ancient, fossilized microbes or modern, living ones on Mars, one must drill down at least a couple of meters (about 6 feet) into the soil. Scientists don't expect to find any hint of biological organisms at the surface since the strong ultraviolet radiation hitting the planet would have caused any organic molecules to oxidize long ago. The carbon from any biological life would have turned to carbon dioxide as it was oxidized over time, vaporizing into the Martian atmosphere. But if microbes did evolve on Mars, then "their biomolecules could still be in the fossil record, or they could be in permafrost," says Wynn-Williams, "and if we drill a hole in the surface of Mars, and lower down the detector head of one of these little Raman spectrometers, we should be able to recognize the fingerprints of the same sort of pigments that we find in these microbes in the Antarctic."
It is possible the Raman spectrometer will fly on a 2005 mission to Mars aboard the Mars Express Lander sponsored by the European Space Agency. The instrument's probe would be housed in metal casing called a mole, which drills itself down into the ground. A side window in the mole would allow the spectrometer to take readings of each layer of soil as the mole digs deeper and deeper into the Martian ground.
Before flying to Mars, however, the spectrometer will head to the Antarctic dry valleys which are remarkably similar to present day Mars. Testing the spectrometer on the cyanobacteria in Antarctica will give scientists a library of chemical signatures or fingerprints for microbes in the Antarctic soil. Any chemical fingerprints the spectrometer finds on Mars can be compared to the library of Earth microbes.
Not only will the spectrometer identify any microbe it finds by the pigments it detects, but it can also help scientists say something about the bacteria's environment, its ecosystem. The spectrometer can identify the chemical composition of the soil or rock in which a microbe either became fossilized or currently lives.
Because pigments can last seemingly forever, far beyond the life of the organism from which it came, and because they apparently are molecules produced only by living things, pigments can be referred to as biomarkers. Using the pigments as biomarkers allows scientists to address the question: "will we be able to recognize life on other planets if we find it?"
"The reason I'm zeroing in on pigments is we know we can detect them," Wynn-Williams says. "The chances are that life originated on Earth and on Mars in a geothermal environment, near black smoker vents, but it's difficult to recognize it definitively. You need a really strong signal of some sort, which says 'this was life.'"
Pigments fit that bill. Anything that lives near the surface of a planet is exposed to sunlight. It has to produce pigments of some kind to protect itself from ultraviolet radiation and/or to harness solar energy to produce chemicals for food. One way or another pigments are essential to living things at a planetary surface. The Raman spectrometer is the ideal instrument for detecting the signals produced by pigments from microbes, either alive or dead.
It is up to the people who interpret those signals to decide: if we detect the presence of pigments on Mars, will that be enough evidence to say with certainty that life originated and evolved there? Are we still alone? Or would pigments on Mars possibly be the remains of our ancient brethren?
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