Extraterrestrial objects colliding with Earth’s ancient oceans may have sparked the molecules necessary for life.

Thoughts of meteors hurtling toward Earth usually generate visions of mass extinctions. But some recent studies paint a new picture: Large rocks hurtling in from space may have actually helped spark life on Earth.

Nobody would call early Earth a friendly place. Billions of years ago, it started as a red-hot sea of molten rock. But then the surface cooled enough for oceans to form. During that era meteorites slammed into Earth about 1,000 times more frequently than they do today.

While these conditions might not seem conducive to life, scientists say they may have been just the recipe needed to jump-start a few life-producing chemical reactions.

Geochemist Yoshihiro Furukawa at Tohoku University in Sendai, Japan had a theory about how this could happen. When large extraterrestrial objects crashed into Earth’s ancient oceans, they produced enormous heat and pressure that caused objects to vaporize, or turn into gas. Furukawa thought such powerful events may have triggered chemical reactions that generated organic molecules from basic ingredients. To test this theory, he and his colleagues designed a study.

To simulate the power of a collision between an extraterrestrial object and an ancient ocean, the scientists used a propellant gun. It keeps objects under high pressure, and when the pressure is released, the gun’s contents are expelled at high speeds.

To get the right recipe for such a collision, the scientists combined ingredients commonly found in meteorites and in Earth’s ancient oceans and atmosphere. The scientists mixed carbon, iron and nickel — elements found in the most common type of meteorites — with water, ammonia and nitrogen, which were present in early Earth.

The team placed these ingredients inside stainless steel canisters and used the gun to fire them at solid targets. The canisters reached speeds of more than 1 kilometer per second.

The researchers hoped to see how a high-temperature, high-velocity impact affected various mixtures of the ingredients. When canisters were fired at the target, the temperatures inside became scorching. They briefly rose to about 4,700 degrees Celsius (nearly 8500 degrees Fahrenheit). The pressure generated inside the canisters by the impact was about 60,000 times that of ordinary atmospheric pressure at sea level.

Afterward, the scientists analyzed the contents of the canisters. They recovered a variety of organic molecules, including fatty acids such as those found in cell membranes. The team also found a variety of amines, which are used to create amino acids, the building blocks of life. One test even generated a type of amino acid, called glycine, which is commonly found in proteins.

The study shows how conditions on the Earth 4 billion years ago may have spurred amino acid synthesis, or production. Scientists say the study sheds new light on how and when organic molecules appeared on the young Earth. Previous studies have hinted that lightning striking Earth’s ancient atmosphere could have generated organic molecules necessary for life as well. And such studies have also suggested that the chemical reactions around deep-sea hydrothermal vents — where water heated inside the Earth is expelled from cracks in the sea floor — could have produced these molecules.

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 .

How did life forms get so complicated? Scientists at Pennsylvania State University may now have part of the answer. The secret ingredient could be the oxygen in Earth’s atmosphere.

Example of a plant cell, stained and viewed under a microscope.

The researchers found a relationship between the number of cell types in organisms and the quantity of oxygen in Earth’s atmosphere. The more oxygen there was, the more complex the organisms could become.

Early in Earth’s history, there was very little oxygen in the atmosphere. Only simple, single-celled organisms such as bacteria were around. Then, about halfway through Earth’s history (2.3 billion years ago), oxygen began to accumulate in the planet’s atmosphere. Around the same time, organisms with several types of cells appeared.

Researcher S. Blair Hedges says this happened because of an important change in the structure of cells. Some cells developed features called “mitochondria.” These are the little power plants inside cells. They use oxygen to generate energy.

Mitochondria were essential for organisms to become more complex. “It makes a lot of sense,” Hedges says, “because to have complex organisms, you need energy.”

Later, about 1.5 billion years ago, there was another change in cells that enabled organisms to become even more complex. Some cells developed features known as plastids. These are the parts of cells that enable plants to produce oxygen through photosynthesis.

The plastids boosted the amount of oxygen in Earth’s atmosphere. With more oxygen available, mitochondria could generate more energy.

Hedges and his colleagues estimate that organisms with up to 10 cell types emerged with the help of plastids. And the numbers kept growing. By 1 billion years ago, organisms with up to 50 cell types had appeared, the researches say.

Fossils had suggested that a big jump in the complexity of organisms took place 600 million years ago. If the estimates by Hedges and his colleagues are correct, life actually started on the road to complexity a lot earlier.—S. McDonagh

Going Deeper:

Travis, John. 2004. Gassing up: Oxygen’s rise may have promoted complex life. Science News 165(Feb. 7):85. Available at http://www.sciencenews.org/20040207/fob5.asp .

You can learn more about animal and plant cells at www.enchantedlearning.com/subjects/plants/cell/ (Enchanted Learning) and www.cellsalive.com/toc.htm (Cells Alive!).