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Retrospections Astrobiology Top 10: Ancient Footprints in the Salt
 
Astrobiology Top 10: Ancient Footprints in the Salt
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Origin & Evolution of Life
Posted:   12/24/08
Author:    Aaron L. Gronstal

Summary: Astrobiology Magazine is looking back over 2008, highlighting the top 10 astrobiology stories of the year. At number 10 is the discovery of ancient organism remnants preserved in salt crystals. The surprising finding could help astrobiologists search for signs of life on other planets. (This story originally was published on July 31, 2008).
This is a TEM image taken of the water, or inclusion brine, inside the halite crystals. It's easy to see that the brine is full of fibers.
Credit: Griffith et al., 2008

Scientists have long searched for traces of ancient life on Earth in order to understand the history of life on our planet. Fossilized bones have helped us understand the age of the dinosaurs. Insects trapped in drops of amber have inspired Hollywood films and researchers alike. These remnants of ancient life on Earth provide important clues about our planet's past.

Now, a team of researchers working in New Mexico has found traces of life inside salty halite crystals. The discovery is "an invaluable resource for understanding the evolutionary record [of Earth] over a geological time frame," according to Jack Griffith of the University of North Carolina, Chapel Hill and his colleagues, who recently published their work in the journal Astrobiology. The finding may even help scientists search for signs of life on other planets.

Halite is more commonly known as 'rock salt', and can be found all over the planet in the form of salty crystals. These crystals may not seem all that interesting at first glance. However, inside of them are tiny pockets of water that can be very valuable for scientists. Halite crystals form in liquid as evaporation occurs. The crystals naturally trap small amounts of liquid during this process. These water pockets and all that they contain can be protected inside halite crystals for extremely long periods of time. The crystals in the recent study had drops of water that were 250 million years old.

Salty Cellulose

Ancient cellulose fibers were also collected from solid halite by centrifugation and photographed using a TEM microscope.
Credit: Griffith et al., 2008

The halite crystals have kept these tiny water drops safe for an astonishing length of time…but the story doesn't end there. Scientists discovered abundant amounts of cellulose fibers inside the water. Cellulose is present in many living cells. One of the most common places to find cellulose is as a component in the cell walls of plants. Cellulose is also produced by single-celled organisms like cyanobacteria. Most importantly for astrobiologists, cellulose is only formed by living organisms. If cellulose is present, there must have been life.

Luckily for the research team, cellulose is a very sturdy material and the fibers were stable enough to survive until today. Additionally, the samples were collected from deep below the ground, where they had been protected from radiation. The cellulose found in the New Mexico halite is now the oldest biological macromolecules ever isolated. In addition, the researchers were able to visualize the fibers and study their biochemistry. Because of this, the 250 million-year-old cellulose is now providing a window into the history of life on Earth.

Mars with Salt

Griffith and the ancient salt samples. Remnants of life have provided us with valuable information about the history of our planet's climate and biosphere. One day, similar methods may help astrobiologists identify signs of past life on other planets.
Credit: UNC

If cellulose can survive for 250 million years inside halite on Earth, it may be possible for similar molecules to survive in halite crystals on other planets.

Cellulose is a common component in organisms on Earth. According to the authors of the study, "over 100 gigatons of cellulose are produced each year" on our planet. It is used by bacteria to make biofilms. Plants and algae use cellulose to help build their physical structures. The bodies of insects contain a molecule very similar to cellulose called chitin. If life on other planets is similar to life on Earth, it is possible that alien organisms might use molecules similar to cellulose. As this new study shows, these molecules could possibly survive for millions of years, even if their home planet is no longer habitable today.

If we can find halite on other planets, the crystals may be an excellent place to search for proof of ancient life. The researchers are hoping to examine even older samples of halite on Earth in the future to determine if biomolecules like cellulose can survive even longer inside the crystals. If future studies are successful, halite crystals could become an important target for future exploration missions to Mars and beyond.


Related Web Sites

Astrobiology Roadmap Goal 7: Signatures of Life
Fossil Hunting on Mars
A Pregnancy Test for Mars
Dry Limit of Life
Journey to Another Planet


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