Life Before Life
“What Came Before DNA?” [June] painted a far-too-rosy picture of life arising as proposed by Jack Szostak and Steven Benner’s theory. For example, it is stated that “under the appropriate conditions, phosphate reacts with ribose and nucleobases to form a large organic molecule called a nucleotide.” That statement is misleading because the only “appropriate conditions” known to do this occur in actual living cells, and they use protein enzymes—which are not applicable to the origin of life—to do so. Also, the type of experiments being referenced use preactivated nucleotides, and the plausibility that the main preactivating substances are chemical precursors of the origins of life is questionable at best. Another important point is the low probability of hitting upon an RNA sequence capable of serving the RNA replicase role. The closest thing to an RNA replicase produced by directed evolution (mentioned in the article) is about 180 nucleotides long. Even if we assume that a trillion trillion trillion trillion unique sequences 180 nucleotides long could function as RNA replicases, the probability of hitting any one of them in a single shot is still only about 1 in 1060.
Many of Rick Pierson’s comments are correct, in particular his identification of what scientists call the water problem: the fact that the reaction of a phosphate with ribose and nucleobases to form a nucleotide is energetically uphill in water. In other words, creating nucleotides from their components in water is like pushing a rock uphill, while the reverse reaction, the conversion of nucleotides to their pieces in water, is like rolling a rock downhill. This is the next big problem in prebiotic chemistry, and we need some good ideas to solve it. We do not know the chances of finding an RNA replicase within a collection of random RNA sequences. If they are low, then few examples of RNA-originating life will be found in the 1011 stars in each galaxy in the 1012 galaxies in the universe. We are still some distance from understanding how life might emerge in general, and we may never know how life emerged on Earth specifically. But there is reason to hope that the statistics of RNA catalysis are not as bad as Pierson suggests. —Steven Benner
Fuel for Thought
I was pleased to read how determination and the support of community and government were weaning the people of Samsø from fossil fuels [“[Green]mark,” June]. I was not pleased to see, once again, that hydrogen is linked only with fuel-cell technology, which is “many years away” from mass production and costs several times as much as internal combustion technology. Why do people fail to consider hydrogen as an internal combustion fuel? For as little as $3,000, gasoline-powered internal combustion engine (ICE) cars can be converted to burn hydrogen. Converting to ICE hydrogen vehicles means that we can get the hydrogen infrastructure and renewable hydrogen technology up and running as soon as possible, so that if and when fuel cells take over, we’ll be ready for them.
On the consumption end, burning hydrogen in internal combustion engines is indeed much simpler than using it to power fuel cells. Mazda and BMW for instance have been quite successful at converting gasoline engines into hydrogen engines. Either way, however, the supply end is a problem. At present there are two practical ways to make hydrogen: by reforming fossil fuels and by splitting water via electrolysis. The former doesn’t get rid of fossil-fuel consumption, of course; it just shifts the location of the consumption. Reforming should be somewhat cleaner than burning the fuel directly, but it is also much more complicated and expensive. Electrolysis requires a great deal of electricity, and the amount of energy you get out from the hydrogen is (according to the laws of physics) less than the amount you consume in electricity. Regardless of the approach, hydrogen power is not yet practical, which is why the planners on Samsø have decided to leave petrol-burning vehicles in place for the time being.
I hate to complain when someone writes a wonderful article about math, especially when he cleverly cloaks it in terms of a best seller so that a lot of people will read it [“Cracking The Da Vinci Code,” June]. But in the inset “How the Greeks Found j,” there are some errors. First, you say that the decimal expansions of the two roots of x begin to differ when you calculate them out to several decimals. It is fairly easy to show with arithmetic that the fractional parts—and their decimal expansions—have to agree perfectly, no matter how many digits you compute. Also, you say that the negative solution is equal to 1 – 1/j(where j [phi] is the positive solution). The correct statement is “the negative solution is equal to –1/j.”
STEPHEN K. JOHNSON
The negative root of the quadratic is indeed –1/j. Preoccupied with correcting all those false claims about the golden ratio, I copied and pasted the algebra box directly from an old passage and fell victim to the classic danger of reading what I thought was there rather than what actually was there. Well done for spotting this. My only defense is the old Tom Lehrer quip (from the song “New Math”): “The important thing is to understand what you’re doing rather than to get the right answer.”
The Scourge of Spam
I hate spam as much as anyone, but I think Cynthia Dwork’s idea to further overburden our PCs is ridiculous and irresponsible [“Winning the War on Spam,” Emerging Technology, June]. Adding puzzle solving to sending e-mails is a ludicrous idea for retarding the spread of spam. At best it will only slow down the massive amounts of spam clogging the Internet; at worst it will cause big interruptions in the other uses of our PCs. A much better solution is to block spam completely, at its source, rather than just trying to slow it down a bit. We should change from the simple mail transfer protocol (SMTP) we now use to a protocol that enforces authentication of the sender. Include a valid return e-mail address in the protocol that the e-mail server checks before sending the e-mails. If the return address is not good, the e-mail just gets thrown out. Spammers will be forced to get valid return addresses that can be traced and enforced.
Old Bridge, New Jersey
We erroneously stated in June’s Discover Dialogue that planetary scientist Steve Squyres was a member of the imaging team for Voyager’s encounters with Jupiter and Mars. Voyager has not traveled near Mars. The inset photograph of a badger on page 11 of the June issue (see “Badgers vs. Saxons on Salisbury Plain”) is of the wrong species. The animal shown is an American badger rather than a European badger.
To read more letters (all Web-exclusive) on this month’s features and departments, see www.discover.com/letters.