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4 Life Detection Techniques
Pages 49-62

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From page 49...
... The pyrolytic release exposed the soil to a solar simulator light source and radiocarbon monoxide and dioxide and looked for incorporation into complex organics, which would indicate the presence of life. The labeled release provided some common organic substrates used by biology and looked for the conversion of these to any kind of gas, such as CO2.
From page 50...
... Oscillations in the data were attributed to uptake by minerals in the wet soil due to temperature variations by the abiotic side, while the biological side suggested it could be a circadian rhythm. The control sample, which was heated to 160°C for 3 hours, was used as proof by the biological camp, but the abiotic side said that the oxidants could be heat labile, that FIGURE 4.1 Viking Lander 2's labeled release experiment exhibited radioactive uptake after an i ­njection of nutrients, indicating life.
From page 51...
... sample return will let us determine whether or not martian material contains life or the signs of extinct life. The third, unused Viking lander, he said, was also considered for use in a sample return mission.
From page 52...
... recently discovered a huge quantity of shallow permafrost ice in the Utopia Planitia region where Viking 2 landed. Conditions on Mars during the Noachian era (~3.7 to 4.1 Gyr ago)
From page 53...
... Ruvkun called the ribosome a living fossil of the RNA world. These molecules were easy to pull out and perform RNA sequencing on, which could be used to infer relationships between different organisms.
From page 54...
... In 1973, recombinant DNA allowed genes to be created one at a time. Gene sequencing was invented in 1976, allowing for a much faster discovery rate (e.g., approximately 3,000 base pairs of DNA in a typical paper)
From page 55...
... Fossils from other branches in the phylogenic tree, especially in other domains, are difficult or even impossible to find, particularly as one goes further back in time. However, stromatolites, the fossilized remains of macroscopic mats of bacteria, are known to have existed 3.5 Gyr ago, which is relatively soon after the Late Heavy Bombardment 3.9 Gyr ago, especially for fully developed, rather perfected DNA life-forms.
From page 56...
... Within about 30,000 years, 0.001 percent of that ejecta can land on Mars.5 Interestingly, that same study showed that 1 percent of the ejecta lands back on Earth, which could potentially repopulate an Earth sterilized by the effects of the meteorite impact. Ruvkun proposed to take martian soil and extract DNA from it.
From page 57...
... , a bacteriophage virus.7 Two years later, a paper titled "Is bacteriophage phi X174 DNA a message from an extraterrestrial intelligence" was published, which shows that people have been looking at DNA in terms of astrobiology for a long time.8 Another conference participant reported that, MinION, the Oxford Nanopore's portable DNA sequencer, has an error rate of 17 percent and asked how it was being improved. Ruvkun said that the 17 percent error rate is per nucleotide.
From page 58...
... In contrast, they have not been able to remove the backbone charges and obtain an evolvable biopolymer. Conveniently, Benner said, finding polyelectrolytic genetic biopolymers in a sample of water obtained from an alien locale would be trivially easy and, in fact, is the easiest type of potential genetic molecule to find.
From page 59...
... Prebiotic Chemistry The rest of the genetic biopolymer, Benner said, could be anything. However, ribose is clearly one of the best backbone molecules that have been examined, particularly in terms of molecular recognition, although a handful of other possible structures have been found to work analogously (threose and some bicyclic structures are especially worthy of note)
From page 60...
... It should be noted, however, that recent work of Stephen Mojzsis supported by the Foundation for Applied Molecular Evolution-Templeton program found that the amount of dry land on early Earth may be sufficient so as to not enforce this requirement of panspermia. Moving to a different type of chemistry, Benner said that the main problem with life forming in non-aqueous environments, like Titan's hydrocarbon lakes, is solubility.
From page 61...
... On a planet with water, any life will have a genetic biopolymer with a backbone of repeating charges. This type of molecule can be easily concentrated from alien aqueous environments, such as from the plumes of Enceladus, in order to be detected with today's technology.
From page 62...
... He said that he's tested their ability to synthesize minerals using 50 rocks from the "Benner Collection of Fine Rock Specimens" in order to show that his synthesized rocks are comparable to natural rocks. A workshop participant then said that the Mars teams have found mobile phosphate (in the sense that its concentration changes over short distances)


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