A Brief History of Creation (34 page)

But the idea that life might have arisen elsewhere in the universe was not quite dead, and Crick's hypothesis would seem, for a brief spell at least, almost prescient. Two decades after Crick's musing, a rock was found in the Antarctic that would reignite the idea that life might indeed not have originated on this planet, or at least that it was not exclusive to the Earth.

*
An estimated one out of every five people on Earth followed the broadcast.

†
Bragg's record as youngest Nobel laureate was finally broken in 2014 by Malala Yousafzai, who won the Nobel Peace Prize at the age of seventeen.

‡
The term “nucleic acid” is something of a misnomer. It is now known that both DNA and RNA are present as well in prokaryotic cells, which have no nucleus.

§
The use of Franklin's crystallography has become one of the more enduring controversies over ethics in science. Watson and Crick certainly drew upon Franklin's data without her consent, though it is doubtful that she would have objected. Franklin and Crick grew to be good friends in the years following the discovery. When Franklin died of ovarian cancer in 1958, possibly caused by radiation exposure from her X-ray work, she passed her final weeks at Crick's home. In 1962, Crick, Watson, and Wilkins shared the Nobel Prize in Physiology or Medicine for their discovery of the structure of DNA. Franklin was not under consideration, since the Nobel cannot be issued posthumously, and for many years, her vital contributions to the understanding of DNA were overlooked. The perception of her as victim of an overwhelmingly patriarchal scientific establishment was reinforced by Watson's overtly sexist portrayal of her in
The Double Helix
. Watson called Franklin “the product of an unsatisfied mother who unduly stressed the desirability of professional careers that could save bright girls from marriages to dull men. . . . The thought could not be avoided that the best home for a feminist was in another person's lab.” The line is typical of the way Watson described her throughout the book, and a good example of the obstacles women have faced in the laboratory.

¶
Koltsov's theories on genetics led to his denunciation by Trofim Lysenko. In 1940, Koltsov was fatally poisoned by the Soviet secret police. His wife committed suicide on the same day.

#
History is littered with cases of groundbreaking discoveries being initially overlooked by the lay press and general public. Albert Einstein proposed the theory of relativity in 1905, yet his name did not appear in a newspaper until 1917.

LIFE EVERYWHERE

We are made of star-stuff. We are a way for the cosmos to know itself.

—CARL SAGAN,
Cosmos: A Personal Voyage
, 1980

 

S
HORTLY AFTER MOST
of the planets in the Milky Way had formed some four and a half billion years ago, a volcano erupted on Mars, spewing molten lava onto the surface of the planet. As the lava cooled, it hardened into solid rock. For the next half-billion years, the rock lay relatively undisturbed until, one day, an asteroid came crashing onto the planet's surface. The impact was so powerful that the heat from the blast violently compacted the rock, melting away portions of it and creating a series of tiny cracks. The impact also tore the rock away from its resting place below the surface of the planet, and bounced it above the Martian surface.

Four billion years later, another asteroid slammed into Mars. This one struck with such fury that the rock was hurled skyward, through the planet's atmosphere and deep into space. Finally, slowed by the gravitational pull of the sun, and nudged by that of Jupiter, the rock settled into an orbit not unlike that of the planet that had once been its home. It circled the sun for sixteen million years, until one day, just as humans were starting to form permanent settlements along the Euphrates River, its orbit brought it into Earth's gravitational field. The tiny rock, by then no larger than a softball, hurtled down through our atmosphere and embedded itself deep in an ice field in Antarctica.

Another thirteen thousand years passed. Slowly the rock was pushed to the surface by the force of the ice field butting up against a nearby mountain
range, like a splinter being forced from a finger. It came to rest in the Allan Hills region of Antarctica, at the base of the Transantarctic Mountains, one of the largest and least explored mountain ranges in the world.

On a relatively mild December day in 1984, a team of meteorite hunters from NASA's Johnson Space Center in Houston began combing the area around Allan Hills known as the Far Western Icefield. Since the early 1970s, NASA had sent dozens of such missions to the Antarctic, which had long been recognized as an ideal place to find meteorites. The extreme environment meant that it was relatively sterile compared to almost anywhere else on the Earth's surface, minimizing the dangers of contamination. And the vast flat sheets of pristine white ice that blanketed most of the Antarctic meant that meteorites were easy to spot.

The person who spotted the Mars rock was a novice meteorite hunter named Roberta Score, on her first such expedition for NASA. It was the middle of summer in the Southern Hemisphere, clear and warm for the coldest point on Earth, almost above freezing. She spotted it in the distance, blue in the sunlight and barely bigger than a softball, likely unnoticeable in any other place on Earth. Score retrieved it and gave it a name: Allan Hills 84001, or ALH84001 for short. Score also took a few notes. She noticed that the rock was “covered with dull fusion crust. . . . Areas not covered by the fusion crust have a greenish-gray color and a blocky texture.” Years later, when the rock attracted serious scientific scrutiny, the blocks that Score had observed would become the center of what, for a time at least, seemed like one of the most important discoveries in the history of science.

When the expedition returned, ALH84001 was shipped back to Johnson Space Center. It was placed in the containment facility originally built to contain the lunar samples brought back by
Apollo 11
, where it sat along with the agency's rapidly growing collection of meteorites. Initially, nobody at Johnson suspected that ALH84001 was anything more than a typical meteorite composed of leftover debris from the formation of the solar system, something that had come loose from an asteroid. A chip of it was parceled out for display to the Smithsonian National Museum of Natural History, where it sat, rather unremarkably, for the next five years.

In 1990, a young Smithsonian curator charged with doing some more detailed tests on the composition of the little meteor fragment found that it abounded with carbonate minerals. Although they can be produced through nonbiological means, carbonates on Earth are almost always found in areas that have been exposed to water. This was the first real clue that ALH84001 might be anything but a run-of-the-mill meteorite.

By 1993, mineralogy, isotopic composition, and analyses of trace gases trapped inside the rock had established that ALH84001 was indeed a
Martian
meteorite. It was certainly not the only Martian rock to have fallen onto the Earth. But the technology used to identify extraterrestrial rocks was relatively new, and out of the thousands of meteorites that had been studied by that time, only nine had been conclusively identified as Martian.

ALH84001 began to draw serious attention from labs and research institutions around the world. Pieces were parceled out for study in the United States and abroad. Scientists in Germany were the first to estimate the age of the rock using radiometric dating. They judged it to have formed four and a half billion years ago. This assessment did not quite establish it as the oldest known rock in the universe; another Martian meteor was found to be a tad older. But because of a margin of error that ran in the tens of millions of years, it very well might have been. In any event, over the next several years, ALH84001 became, in the words of one observer, “the most studied 2 kilograms of rock in history.”

The biggest piece was reserved for analysis at NASA, where it fell under the responsibility of geologist David McKay. McKay was chief scientist for astrobiology at Johnson Space Center, and an old hand among astrobiology scientists. He had been a doctoral student at Rice University and had stood in the auditorium when John F. Kennedy delivered what would come to be known as “the moon speech” in 1962.
^*
About a decade later, McKay led one of the research groups established to study the lunar samples from
Apollo 11
. He would also later play an important role in NASA's
Mariner
and
Viking
missions to Mars.

During the
Mariner
and
Viking
missions, McKay helped spot signs that rivers and lakes had once existed on Mars. The possible presence of water was enticing for McKay and other exobiologists looking for traces of life. Water is essential for life—at least life as we know it. It makes up 80–90 percent of almost all living creatures, and it would be hard for any scientist to conceive of a living thing in its absence. But the
Mariner
and
Viking
missions also found the surface of Mars to be a hostile place, at least from the perspective of Earth life. For billions of years, the atmosphere of the planet had been stripped by the constant bombardment of asteroids, like the one that hurled ALH84001 into space, and the incessant solar wind. The atmospheric pressure on Mars was simply too low to support standing liquid water on its surface. If water had ever existed there, it had long since disappeared, either by evaporation or by sinking slowly into Mars's subsurface.

But ALH84001 was a very old rock, formed at a time when Mars was a very young and very different planet. The carbonate mineral deposits piqued McKay's interest. On Earth, carbonate minerals form almost exclusively in the presence of water. To McKay, that likely meant that sometime early in the history of Mars, water had seeped into the rock. And where there was water, there could very well have been life.

McKay was intrigued by the fact that the carbonate minerals were concentrated on the greenish blotches that Roberta Score had noted when the rock was first found. They resembled the kinds of traces left behind by the
Cryptozoon
found by Charles Doolittle Walcott in the Grand Canyon a century earlier. Soon, NASA scientists discovered something that intrigued them even more: tiny crystals of magnetite. These were embedded in cracks in the rock and concentrated around the markings first observed by Roberta Score. The crystals bore a striking resemblance to those left behind by magnetotactic bacteria that teem in the Earth's oceans.

Humans started using the Earth's magnetic field as a means of navigation and orientation only about a thousand years ago, but a variety of organisms in the natural world have been doing it for millions of years.
There is a great deal of evidence that birds, bats, and bacteria use magnetized iron minerals such as magnetite—or “lodestone,” from the Old English for “leading stone”—to orient themselves according to the Earth's magnetic field. The tiny crystals seen in bacteria are called magnetosomes, and they are present in diverse types of microbes, suggesting that these internal compasses are very ancient in origin. Fossil remains of these structures have been found in terrestrial rocks believed to be almost two billion years old.

On Earth, the little grains of magnetite would usually be considered biomarkers, indicators of living organisms. McKay's team decided to send a sample of ALH84001 to Stanford University, where a chemist named Richard Zare had invented a laser mass spectrometer capable of identifying chemical compounds without the invasive and damaging steps necessary in traditional analysis. Zare came back to them with fascinating news: the rocks were filled with organic compounds called polycyclic aromatic hydrocarbons, or PAHs. Although they can be by-products of fossil fuel combustion, PAHs are also often associated with the decay of ancient microorganisms. In private at least, members of McKay's team began to speak about the possibility that they had in their hands proof that life had once existed on a planet other than Earth, what could turn out to be one of the most important discoveries in history.

To make such a startling claim, the NASA scientists needed to identify an actual fossil of a Martian bacterium on ALH84001. But a year of intensive analysis had yielded nothing that looked like any fossil that had ever been found on Earth, so McKay decided to do something nobody else had thought of: he decided to look for something
smaller
.

In January 1996, McKay gained access to one of the most powerful electron microscopes in the world, used by NASA engineers to search for microscopic flaws in hardware on the space shuttle. ALH84001 became one of the first rocks ever examined with the high-power instrument. Over the coming months, McKay was able to make out tiny structures that resembled terrestrial bacteria. But these were
extremely
tiny, the smallest just a hundred-thousandth of a millimeter long. Fifty of the largest, placed side by side, would fit comfortably in a human blood cell. The most interesting
of the bunch was intriguingly wormlike. This one would later form the basis of the seminal photo accompanying their discovery, and it would be seen around the world.