Life on Mars, Life on Earth September 9, 2002
Treasure Hunt
Some people have made it their business to try to catch shooting stars. Space-rock hunters scour Earth's most extreme terrains — such as the Sahara Desert and Antarctica — in search of rare meteorites. NASA announced in January that two rock hunters from France had found perhaps the rarest prize — five new meteorites from Mars. It's estimated that about 20,000 meteorites strike Earth each year, but few come from Mars, making Martian meteorites far rarer than flawless diamonds. The total number of Martian meteorites found on Earth to date is just 24.

Mars has long captured the human imagination. It has been held up as the one place in our solar system — other than Earth — most likely to harbor life forms. In the 1700s, astronomer William Herschel — one of the first people to write about extraterrestrial life — speculated that Martians lived in conditions similar to those on Earth. In the late 19th century, people observing Mars from Earth noticed canal-like patterns on the planet's surface and theorized that these canals had been built by great civilizations. We now know that there are no canals on Mars' surface, and investigations by probes and landers have found no evidence of Martian civilizations. But there are hints that Mars may have supported life forms of some kind at some time in its history — or perhaps even today. Martian meteorites found on Earth continue to provide us with clues.

In 1996, NASA scientists announced that a Martian meteorite contained what appeared to be evidence of primitive life. The meteorite, known as ALH84001, had been found 12 years earlier in Antarctica. It's the size of a potato and weighs about 4 pounds. When ALH84001 was first collected, it was dismissed as a typical meteorite originating from the Asteroid Belt between the orbits of Mars and Jupiter. But a random sample of ALH84001 done years later led scientists to perform more detailed analyses, which revealed that this was no ordinary meteorite. A flurry of excited activity ensued in the worlds of both science and science fiction.

The small, tubular features in the above electron microscope photograph of an ALH84001 sample are thought by some to be microscopic fossils of bacteria-like organisms that may have lived on Mars more than 3.6 billion years ago. These features measure about 1/500 the diameter of a human hair.

ALH84001 also contains an unusual abundance of organic-compound carbon, as well as types of minerals and mineral features that might be caused by biological activity. Just last month, NASA astrobiologists announced that 25 percent of the magnetite found in ALH84001 can only have been formed by bacteria. The particular form, size, shape, and purity of the magnetite crystals is only formed on Earth by bacteria working in Earth's magnetic field. The Mars Global Surveyor spacecraft has provided evidence that early Mars did have a magnetic field.

These findings added to the body of evidence that Mars was liveable at some point in its history. In 2000, Mars Global Surveyor returned images of gullies and deltas on Mars' surface, suggesting that rivers once ran over parts of the planet's surface — perhaps millions of years ago, or perhaps more recently. On top of this, there is evidence that the thin Martian atmosphere was once much denser and, therefore, able to sustain life.

But what of today? As recently as May, the Mars Odyssey orbiter returned remote sensing data showing large deposits of water ice, buried one to two feet beneath the planet's surface. With its tenuous, oxygen-starved atmosphere and apparent lack of liquid water, Mars would seem to no longer be the ideal neighborhood for life forms. But in fact, there is still a chance that life might be found on Mars today — and the shape these life forms take may be quite similar to those found on Earth.

Space Rocks on Ice
Three-fifths of the meteorites collected on Earth to date have been collected in Antarctica. That isn't because more meteorites fall there than elsewhere on Earth. But meteorites that do fall on Antarctica and get trapped in the ice work their way up to the surface over thousands of years. And that's where researchers find them, black rocks sitting on the white ice, ready for collecting!

The Face on Mars

Sometimes imagination and wishful thinking can get the better of a person. Take this photograph for example. This is a close-up view of the surface of Mars taken by the Viking 1 orbiter spacecraft in 1976. Many people said that this was clearly a picture of a huge face, a mile across, sculpted out of the Martian landscape. Perhaps, they continued, this was a sign that there was or is intelligent life on Mars. However, subsequent photos taken by a different orbiter with different lighting conditions and better data transmission showed that this feature is an unremarkable hill, without a nose, eyes, or mouth.

The powerful idea of a giant face sculpted on Mars' surface was used in the 2000 movie Mission to Mars, which starred Tim Robbins and Gary Sinise.

Extreme Bacteria
The life forms in question are bacteria and, here on our planet, they live in conditions as harsh as any Mars can offer. These bacteria live miles underground and don't need oxygen to survive. They live on hydrogen, chemicals from rocks, and thermal energy. As such, they are on the fringe of "life as we know it."

In findings published in the journal Nature earlier this year, researchers describe a community of bacteria that they located hundreds of feet below the Beaverhead Mountains in Idaho. The single-celled organisms, known as Archaea, live around bubbling hot springs where water temperatures reach almost 140 degrees Celsius. They live without light or oxygen; instead, they consume the hydrogen produced by the reaction between hot water and bedrock. With their unusual lifestyle, these microbes — and others like them — would probably do well in a place like Mars.

The Idaho microbes are not alone: many other places on Earth harbor similar life that does not depend on sunlight and photosynthesis. Bacteria live on basalt buried more than a mile beneath Earth's surface and inside rocks in harsh climates like those in the Arctic or in deserts. Researchers have seen earthquakes release clouds of living microbes from rocks buried as far as five miles beneath the ocean floor. Microbes have also been discovered in a frozen lake more than two miles beneath the ice of Antarctica, a place where no light has penetrated for millions of years.

  • Read about life that flourishes in the depths of the oceans in "Life Without Light," an article from the Digital Learning Center for Microbial Ecology.

With life finding its way in such unlikely parts of our own planet, it's not a great stretch to imagine that life might also persist on Mars' rocky outcrops or beneath Europa's icy surface. But scientists aren't stopping there: they are considering a much more fundamental connection between life on Earth and life on Mars.

Survival of the Simplest
Some scientists argue that life on Mars may have "seeded" life on Earth, or vice versa. Could life from Mars have traveled to Earth? Could all life on Earth have started with life from Mars? These are controversial questions, probing at the very origins of life on our planet. But suppose Martian meteorites did contain living organisms. Would it be possible for those organisms to survive a journey through space, locked away inside a rock spaceship?

Start with a hypothetical rock just below the surface of the red Martian soil. The rock is ordinary except that it has some form of microscopic life living on it or inside it. Suddenly, Mars is struck by a comet or by a swarm of asteroids. The rock, tossed off the surface of Mars by the enormous impact, gets hurled into space where it spends millions of years being subjected to lethal radiation, airless vacuum, and freezing cold.

Eventually our hypothetical rock encounters Earth's gravitational pull and falls through Earth's atmosphere at speeds of 25,000 miles per hour or more. The heat of this kind of reentry is enough to burn up most meteors before they can ever reach Earth's surface. This rock, however, survives reentry, streaks across the sky, and lands — a Martian meteorite.

Could any kind of life, even microscopic life locked inside a blackened meteorite, survive such a tortuous journey? It is possible. So, if there were simple forms of life on Mars billions of years ago, it is feasible, although highly unlikely, that they could have hitched a ride to Earth and helped "seed" or start life on this planet.

More Links
Visit the Astrobiology Web to find out more about life in extreme environments.

For a look at how an asteroid or comet impact on Mars might have ejected material that eventually fell to Earth as a meteorite, see the Life from Mars video produced by NASA. (Requires Real Player. Download now.)

When did this fascination with Mars (and Martians) begin? At NASA's Planet Mars in Popular Culture, take a look at how our curiosity and imagination have led us from astronomer Giovanni Sciaparelli's observation of channels on Mars to H.G. Wells's The War of the Worlds and movies such as Total Recall and Tim Burton's Mars Attacks!

Check out's Exploring Mars site! You'll find continuing coverage of NASA's missions to Mars, featuring articles, photos, movies, and virtual reality explorations, such as a simulation of driving the Mars rover Sojourner. There are also games and an interesting feature where you can hear what familiar sounds might sound like if you were hearing them in Mars' thinner atmosphere!

Such questions about life on Mars are pushing scientists to think in new and different ways. One traditional problem with the sciences is that the different science specialties, such as astronomy or physics or biology, rarely have much interaction with the other specialties. NASA's Astrobiology Institute attempts to get scientists from all different fields together to better understand the origin of life's building blocks.

Scientists will be examining the recently discovered Martian meteorites — one of which is called NWA 1068 — to see if they hold any further clues about life on the red planet. And in the process, they may learn more about life on Earth, too.

Related Activities
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The Odyssey Arrives
Read about the Mars Odyssey in this Riverdeep archive article.
The Broth of Life
This time last year, scientists discovered signs of water on Mars and Jupiter. Find out more in this archive article.