[CraigS]

So, the next piece of the puzzle would be to look at some of the evidence. In pre-emption of being accused of cherry-picking, I’ll state upfront that my reason for zooming in on this bit, is that I just like it ... it intrigues me ... there is objectivity behind it, the results have been scrutinised and peer-reviewed, and the source is reasonably reputable.

So ... onto the 2006 results of the Stardust Probe Return Sample ...

In 2006, the probe returned samples to Earth, taken from the coma of comet Wild 2:

In December 2006, seven papers were published in the scientific journal, Science, discussing initial details of the sample analysis.

Among the findings are: a wide range of organic compounds, including two that contain biologically usable nitrogen; indigenous aliphatic hydrocarbons with longer chain lengths than those observed in the diffuse interstellar medium; abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene, proving consistency with the mixing of solar system and interstellar matter, previously deduced spectroscopically from ground observations; hydrous silicates and carbonate minerals were found to be absent, suggesting a lack of aqueous processing of the cometary dust; limited pure carbon (CHON) was also found in the samples returned; methylamine and ethylamine was found in the aerogel but was not associated with specific particles.

However, in 2009 the following was announced:

Glycine amino acid discovered in Comet Wild 2 sample:

From Wiki:

Glycine (abbreviated as Gly or G) is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG.

So there was some question about contamination of the sample. However, this was answered by isotopic analysis:

Isotopes are versions of an element with different weights or masses; for example, the most common carbon atom, Carbon 12, has six protons and six neutrons in its center (nucleus). However, the Carbon 13 isotope is heavier because it has an extra neutron in its nucleus. A glycine molecule from space will tend to have more of the heavier Carbon 13 atoms in it than glycine that's from Earth. That is what the team found.

"We discovered that the Stardust-returned glycine has an extraterrestrial carbon isotope signature, indicating that it originated on the comet," said Elsila.

Very interesting, eh ?

For me, this is pretty close to the mark (but still arguably, by no means, conclusive).

Cheers