Possible Key to Life's Chemistry Revealed in 50-Year-Old Experiment

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Possible Key to Life's Chemistry Revealed in 50-Year-Old Experiment

by Wynne Parry, LiveScience Senior Writer

Date: 21 March 2011 Time: 03:01 PM ET

An old experiment, rediscovered after more than 50 years, may demonstrate how

volcanoes – and possibly chemical reactions far from primitive Earth in outer

space – played a role in creating the first amino acids, the building blocks of

life.

In 1953, chemists Harold Urey and Stanley performed a landmark experiment

intended to mimic the primordial conditions that created the first amino acids,

by exposing a mix of gases to a lightning-like electrical discharge. Five years

later, in 1958, performed another variation on this experiment. This time

he added hydrogen sulfide, a gas spewed out by volcanoes, to the mix.

[scientists Hunt for Signs of Earliest Life on Earth]

But for some reason, never analyzed the products of the hydrogen sulfide

reaction. About half a century later, 's former student Bada, a

marine chemist at the Scripps Institution of Oceanography in California,

discovered the old samples in a dusty cardboard box in 's laboratory,

which Bada had inherited. ( passed away in 2007.)

Using modern analytical techniques, Bada and his team, which included

, then at Scripps, analyzed the products of the reaction, which were

housed in small vials. They found an abundance of promising molecules: 23 amino

acids and four amines, another type of organic molecule. The addition of

hydrogen sulfide had also led to the creation of sulfur-containing amino acids,

which are important to the chemistry of life. (One of these, methionine,

initiates the synthesis of proteins.)

The results of the experiment – which exposed a mix of volcanic gases, including

hydrogen sulfide, methane, ammonia and carbon dioxide gas to an electrical

discharge – tell us that volcanic eruptions coinciding with lightning may have

played a role in synthesizing large quantities and a variety of biologically

crucial molecules on the primitive Earth, , now a graduate student at

Georgia Institute of Technology, told LiveScience.

" The gas mixture used in this experiment was likely not ubiquitous

throughout early Earth's atmosphere on a global scale, but it may have been

common on a more local scale where there was heavy volcanic activity, "

said.

Parallel to the Urey- experiment

By comparison, the famous Urey- experiment in 1953 exposed hydrogen,

steam, methane and ammonia to an electrical discharge. The initial results

included far fewer organic molecules – only five amino acids. However, Bada and

his team reanalyzed these old samples along with previously unpublished results

with modern techniques, revealing a much greater variety of biologically

important products.

The results of the 1958 experiment, however, show that adding hydrogen sulfide

to the reaction enriches the mixture of organic molecules produced, according to

Bada.

The 1958 reaction – which also incorporated carbon dioxide, a gas not included

in the earlier experiment – created a mix more like that which geoscientists now

believe made up the atmosphere of primordial Earth, said.

From outer space?

Amino acids, which combine to form proteins, which, in turn, form cellular

structures and control reactions in living things, are not unique to Earth. They

have been found on meteorites, mainly from samples acquired from asteroids and

from one comet, according to Sandford, a research scientist at NASA's Ames

Research Center in California.

Bada's team compared the amino acids produced by the 1958 experiment with those

contained in a type of carbon-rich meteorite, known as a carbonaceous chrondite.

These meteorites are believed to provide snapshots of the types of organic

reactions that took place in the early solar system, Bada told LiveScience in an

email.

The researchers compared the amino acids produced by the hydrogen sulfide

experiment with those contained by several carbonaceous chrondites. Some matched

well, while others did not, suggesting that hydrogen sulfide played a role in

the synthesis of amino acids in some solar system environments but not in

others, Bada wrote.

There is a theory that life on Earth got a jump start from organic molecules

when they arrived on the planet from space, Sandford told LiveScience. There is

no doubt that space delivers much of the molecular building blocks for

terrestrial life, but the question is the role the molecules played in getting

life started, he added.

" In the end, if life was trying to get started, my guess is the process wasn't

very picky about where the molecules came from, " Sandford said. " [Early life]

didn't care if that amino acid was formed in space or a lightning strike in

Earth's atmosphere or came out of a hydrothermal vent… So in the end, it is

possible life got started from acquiring building blocks from a wide variety of

sources. "

Sandford's work involves simulating ices found in many environments in space –

including comets – that contain molecules similar to those used in the

Urey- experiment, and bombarding them with ionizing radiation. And like

the reactions believed to have taken place on primordial Earth, these simulated

cosmic ice reactions synthesize amino acids.

" At some level, the universe seems to be hard-wired to create amino acids,

provided you have the right elements present and energy, " he said.

A smelly piece of science history

It's not clear why never analyzed the samples he produced with the

hydrogen-sulfide experiment, but speculates that it may have had

something to do with the rotten-egg odor of hydrogen sulfide.

" When I was working with them by hand I could smell them myself, " said.

" It wasn't so strong that it was overpowering, but it was strong enough to

convince me to not stick my nose in front of it again. "

But, unpleasant odors aside, the experience was a memorable one.

" It is sort of surreal to hold the sample vial in your hands and look at Stanley

's handwriting on the label, " said. " It was a very unique

opportunity to go back in time and look at what he did and be able to use modern

analysis techniques to be able to analyze samples produced over 50 years and see

what they still contain today. "

Their work is published this week in the journal Proceedings of the National

Academy of Sciences.