National Geographic News
photo: Preserved Bull Frog

A bull frog is preserved in a formaldehyde solution (file photo).

Photograph by Phil Degginger, Alamy

Ker Than

for National Geographic News

Published April 6, 2011

Life on Earth may owe its existence to a poison carried across the solar system by asteroids and comets, a new study says.

Formaldehyde (CH2O) is a colorless gas that's often dissolved in water to make a liquid called formalin, used in various industrial products such as building materials, disinfectants, and embalming fluid. (Related: "Lost 'Sleeping Beauty' Mummy Formula Found.")

The molecule doesn't exist for long in its natural state on Earth without human intervention. That's fortunate for us, because formaldehyde easily reacts with other chemicals.

"Formaldehyde is poisonous because it interferes with so many metabolic reactions" and can block critical protein functions in the body, said study co-author George Cody, a chemist at the Carnegie Institution for Science in Washington, D.C.

According to the U.S. Environmental Protection Agency, exposure to formaldehyde can cause breathing problems, nausea, eye irritations, and rashes. The chemical has also been found to cause cancer in lab animals.

But while naturally rare on Earth, formaldehyde is a common molecule in space. (Related: "Largest Space Molecules Found; Buckyball Mystery Solved.")

"It's not as common as, say, hydrogen or water, but it's ubiquitous in the galaxy," Cody said. "Wherever people look for molecules in the galaxy, they see formaldehyde."

Formaldehyde Cooked Up Organic Matter?

Due to its relative abundance and high reactivity, Cody and his team suspected formaldehyde might play a role in the creation of complex, carbon-rich—or organic—molecules found inside asteroids and comets.

Scientists think such bodies might have been responsible for seeding early Earth with essential materials for life to evolve, such as carbon and water.

(Related: "Comet Swarm Delivered Earth's Oceans?")

To test their idea, the team used formaldehyde as a basis for synthesizing the organic materials discovered in certain meteorites—pieces of asteroids that have crash landed on Earth.

The researchers found that the resulting tar-like substance is not only a close match for the meteorite material but is also similar to organic matter captured in 2004 during a flyby of comet 81P/Wild 2 by NASA's Stardust mission.

Based on these findings, Cody thinks interstellar formaldehyde found its way into comets and asteroids during the birth of the solar system. Over time the substance underwent chemical reactions to form complex organic molecules.

These comets and asteroids could have then slammed into our planet during its early years, leaving behind their precious carbon-rich cargo. (Related: "Saturn's Largest Moon Has Ingredients for Life?")

Poison Helped Carbon Survive on Molten Earth

According to one theory, early Earth was little more than a molten mass following a collision some 4.45 billion years ago with a Mars-size object, which likely created the moon. (See "Far-Flung Space Crash May Help Solve Mystery of Moon's Formation.")

While Earth was in this hot, liquefied state, light elements and molecules such as hydrogen, water, and carbon would have evaporated immediately into space.

If the carbon contained in the comets and asteroids bombarding Earth during this phase existed only in the form of simple carbon molecules such as formaldehyde, it would have also quickly evaporated, Cody said.

But if the formaldehyde had been transmuted into more complex organics during its long incubation in space, the resulting molecules would have been heavy enough to avoid this fate.

In their experiments, Cody and his team heated their formaldehyde-based organic material to as high as 2,500 degrees Fahrenheit (1,400 degrees Celsius) and found that it remained intact.

Other carbon-based polymers that they tested broke down into simpler molecules and vaporized when heated.

By forming heavier organics, "formaldehyde gave carbon the capacity to hang on and survive the cataclysmic events in the inner solar system," Cody said.

The formaldehyde study was published in the April 4 issue of the journal Proceedings of the National Academy of Sciences.

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