We know that organic compounds have been found in meteorite fragments. But are they truly extraterrestrial, or the result of contamination here on Earth? The subject, always controversial, has been given new impetus by a paper that points to the former, with interesting ramifications. Did life begin on Earth or was the Earth seeded by life from the cosmos? Or perhaps a third alternative exists, with pre-existing life influenced by infall from outer space. If we can build a viable case for the latter two possibilities, we can build one just as viable for planets around a wide variety of stars, giving the idea that granted enough time, life of some kind may become ubiquitous a most interesting boost.
The scientists involved have been working with fragments of the Murchison meteorite, which fell in 1969 about 100 km north of Melbourne, Australia. Quite a bit of material — over 100 kg — could be recovered, enough for batteries of subsequent tests and the discovery of various amino acids, some common, some unusual. The most recent work finds the molecules uracil and xanthine in Murchison fragments. These are nucleobases, or precursors to the molecules that make up RNA and DNA.
Moreover, they’re found to contain a heavy form of carbon that the team believes could only have been formed in space. And that takes us to some interesting places. Here’s Mark Sephton (Imperial College London), a co-author of the paper on this work, on the possibilities:
“Because meteorites represent left over materials from the formation of the solar system, the key components for life — including nucleobases — could be widespread in the cosmos. As more and more of life’s raw materials are discovered in objects from space, the possibility of life springing forth wherever the right chemistry is present becomes more likely.”
That ‘right chemistry’ is an interesting thing indeed. Accept the idea that the first living organisms on Earth emerged as the result of the chemistry of early organic compounds. Just how that process proceeded is hidden from us by subsequent geological activity, not to mention the bombardment of the planet between 3.8 and 4.5 billion years ago. But the materials involved in the Earth’s formation can be studied in objects like the Murchison meteorite. Carbonaceous chondrites like this are a class of primitive meteorite that contains compounds conducive to life. They offer a snapshot of the organic chemistry that suggests how life began.
The effects of the heavy bombardment all those billions of years ago in jump-starting life on this planet are becoming better understood through finds like these. And they do suggest that we live in a cosmos that keeps trying to get life started wherever conditions are right. Couple that with the discovery (within a few years, surely) of Earth-mass planets in the habitable zones of other stars and the outlook for finding signs of life in future terrestrial planet hunter missions looks brighter and brighter.
The paper is Martins, et al., “”Extraterrestrial nucleobases in the Murchison meteorite”, Earth and Planetary Science Letters, Volume 270, Issues 1-2 (15 June 2008), pp. 130-136
Extraterrestrial nucleobases in the Murchison meteorite
Authors: Zita Martins, Oliver Botta, Marilyn L. Fogel, Mark A. Sephton, Daniel P. Glavin, Jonathan S. Watson, Jason P. Dworkin, Alan W. Schwartz, Pascale Ehrenfreund
(Submitted on 13 Jun 2008)
Abstract: Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of delta13C=+44.5per mil and +37.7per mil, respectively, indicate a non-terrestrial origin for these compounds.
These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life’s origin.
Comments: 31 pages, 4 figures, 3 tables
Subjects: Space Physics (physics.space-ph); Biological Physics (physics.bio-ph)
Journal reference: Earth and Planetary Science Letters 270, 130-136. 15 June 2008
DOI: 10.1016/j.epsl.2008.03.026
Cite as: arXiv:0806.2286v1 [physics.space-ph]
Submission history
From: Zita Martins [view email]
[v1] Fri, 13 Jun 2008 17:06:00 GMT (341kb)
http://arxiv.org/abs/0806.2286
Maybee earth was seaded.. Maybee humanity was dying somewhere else in the galaxy and let the Dna spread trough the galaxy with meteorites.. well.. just a thought.
If lifes building-blocks travel on the meteorites, and beeing spread across vast distances in galaxy, does not that make you feel like there´s a purpose with all this?`
There are some HUGE discoveries to be made in the 21 century… I just cant wait! :D
Meteorite could hold solar clues
A rare type of meteorite that could hold clues to the birth of
our Solar System has been bought by London’s Natural History
Museum.
The Ivuna meteorite, obtained from a US private collection,
has the same chemical make-up from which the Solar System
formed 4.5 billion years ago.
It landed in Tanzania in 1938 as one 705g stone, since split into
samples.
Pieces from the UK sample, the largest in any public collection
in the world, will be removed for study.
Full article here:
http://news.bbc.co.uk/2/low/science/nature/7464583.stm
Organic Matter in Space – an Overview
Authors: E.F. van Dishoeck (Leiden Observatory, Leiden University and Max Planck Institut fur Extraterrestrische Physik)
(Submitted on 5 Jul 2008)
Abstract: Organic compounds are ubiquitous in space: they are found in diffuse clouds, in the envelopes of evolved stars, in dense star-forming regions, in protoplanetary disks, in comets, on the surfaces of minor planets, and in meteorites and interplanetary dust particles.
This brief overview summarizes the observational evidence for the types of organics found in these regions, with emphasis on recent developments. The Stardust sample-return mission provides the first opportunity to study primitive cometary material with sophisticated equipment on Earth.
Similarities and differences between the types of compounds in different regions are discussed in the context of the processes that can modify them. The importance of laboratory astrophysics is emphasized.
Comments: Introductory overview lecture presented at IAU Symposium 251, “Organic matter in space”, held at Hong Kong, February 2008; to appear in IAU Symposium 251 proceedings, Cambridge University Press, ed. S. Kwok et al
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0807.0857v1 [astro-ph]
Submission history
From: Ewine F. van Dishoeck [view email]
[v1] Sat, 5 Jul 2008 12:59:39 GMT (892kb)
http://arxiv.org/abs/0807.0857