Impacts with comets and asteroids were common during the Earth's youth
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Comets could have seeded life on Earth
By BBC News Online science editor Dr David Whitehouse
Thursday, 5 April, 2001, 15:08 GMT 16:08 UK
By simulating a high-velocity comet collision with the Earth, a team of scientists has shown that organic molecules hitch-hiking aboard a comet could have survived an impact and seeded life on Earth.
The results add weight to the theory that the raw materials for life came from space.
"Our results suggest that the notion of organic compounds coming from outer space can't be ruled out because of the severity of the impact event," said Jennifer Blank of the University of California, Berkeley.
Blank and her colleagues presented their findings at the national meeting of the American Chemical Society in San Diego.
New science
The researchers shot a can-sized bullet onto a coin-sized metal target containing a droplet of water mixed with amino acids, the building blocks of proteins.
To date more than seventy varieties of amino acids have been found in meteorites and some in interstellar dust and gas clouds.
It was observed that not only did a good fraction of the amino acids survive the collision, many had been polymerised into chains of two, three and four amino acids, so-called peptides, the first stage of building proteins.
What's more, freezing the target to mimic an icy comet actually increased the survival rate of the amino acids.
The test was designed to simulate the type of impact that would have been frequent during Earth's early history, some four billion years ago, when rocky, icy debris in our solar system accumulated to form planets.
During this violent time much of the debris would have resembled comets - dirty snowballs thought to be mostly slushy water surrounding a rocky core - slamming into Earth at velocities greater than 25 km per second (16 miles per second).
Oblique impact
The severity of the laboratory test was equivalent to an oblique collision with the rocky surface of the Earth, a comet coming in at an angle of less than 25 degrees from the horizon, rather than head on perpendicular to the Earth's surface.
"At very low angles, we think that some water ice from the comet would remain intact as a liquid puddle concentrated with organic molecules, ideal for the development of life," Blank said.
"This impact scenario provides the three ingredients believed necessary for life: liquid water, organic material and energy," she added.
Though it has been estimated that in Earth's early history only a few percent of comets or asteroids arrived at low enough angles, the bombardment would have been heavy enough to deliver a significant amount of intact organic material and water, according to Blank's estimates.
The next hitch-hikers she plans to subject to a shock test are bacterial spores, which some have proposed arrived on Earth via comets to jump-start evolution.
-- Anonymous, April 05, 2001