Adenine: One of Four Nucleotide Molecular Buillding Blocks Connected to Life Has Been Synthesized

Writing in Wired Science, Brandon Keim, has reported: "University of Georgia chemists have modeled a key DNA ingredient's emergence from the primordial soup.

"The ingredient, adenine, (A purine base, C5H5N5, that is the constituent involved in base pairing with thymine in DNA and with uracil in RNA.) is one of four nucleotides that arose during the juvenile Earth's 1.5 billion years of lifeless chemical volatility, eventually combining to form the molecular building blocks necessary for life as we know it.

Adenine is a nucleobase (a purine derivative) with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), and protein synthesis, as a chemical component of DNA and RNA.[1] The shape of adenine is complementary to either thymine in DNA or uracil in RNA.

Keim continues: "Scientists have shown that adenine can be synthesized from large quantities of cyanide in volcano-like environments — something the early Earth had in abundance. But the molecular steps underlying this formation have remained a mystery.

"Enter the University of Georgia chemists, who ran several years of quantum chemical computations on possible cyanide reactions and formulations. The result, published in the Proceedings of the National Academy of Sciences: under the right conditions, just five cyanide molecules can combine to form adenine.

"So — good news for all you amateur origins-of-life-in-a-bottle enthusiasts out there! Now we just need to figure out thymine, cytosine and guanine."

Biodiversity: From So Little So Many

For those of us who are fascinated with the biodiversity of life on Earth, we constantly marvel at the overwhelming diversity of life that has come from such a small portion of the Earth. Below us only some five hundred meters from the planets surface bacteria thrive. The varieties of life increase as the Earth's surface approaches. On the surface is where most of the life exists in a plethora of shapes and sizes that include microorganisms, plants, and animals. And among this great diversity of life there is a constant struggle for existence. The Earth's atmosphere acts like a partially shaded window that lets in only about a tenth of the sun's energy that strikes the Earth. Divide that by a factor of ten and that is the removed from the food web by herbivores; ten percent of that is consumed by spiders and other similar carnivores; some species of birds consume the next ten percent in the form of the spiders, etc., as the process continues until the top carnivores such as lions, tigers, sharks, eagles, etc. exist at the top of the chain only to be consumed themselves by parasites and other scavengers.

On closer observation it becomes apparent that all species are part of two hierarchies. An energy hierarchy, or pyramid consists of plants at the bottom that receive the greatest share of the sun's energy with the largest carnivores located at the very tip of the pyramid.

Biomass makes up the second hierarchy as the plants are once again located at the bottom. The next level consists of scavengers and other decomposers, including bacteria and fungi. Again, the top tip of the pyramid is populated by the largest carnivores. There is a completely different situation when the hierarchy of the oceans biomass is studied. The bottom, or largest portion of that pyramid is occupied by organisms that eat the photosynthetic life. The reason for this is that the photosynthetic organisms are not similar to the plants found on land because they are microscopic single-celled phytoplankton which despite their small size are able to fix more energy from the sun and they have a rapid life cycle. Zooplankton subsist on the phytoplankton but are unable to completely eradicate the phytoplankton. From the zooplankton, the pyramid grows smaller until the very tip is reached and is occupied by the ocean's largest carnivores.

One of the first points of interest drawn from studying the hierarchies is that the largest carnivores are completely dependent on biological diversity.

And the theoretical and experimental assumption taken away from studying diversity is that complex systems can be broken down into increasingly simpler systems. This means that the concept of understanding species and their interdependence is key to the study of biodiversity. And from this realization it can be inferred that a species is a population that consists of members that can interbreed freely under normal conditions. The caveat, under normal conditions is added to exclude consideration of hybrids created under unnatural conditions. This also means that each species is a closed gene pool and is a part of the reality that few if many hybrids occur naturally.

The biological species method of classification is not unambiguous and problem free. The inclusion of the concept of evolution creates exceptions and ambiguities that enter into the biological species method of classification. It is evolution that makes the same reproductively isolated species different from another group of the same species in another location (biogeography-the study of the distribution of biodiversity over space and time)

thus making geography a factor. Another difficulty arises when semispecies are considered because they include aspects of partial interbreeding that create hybrids under natural conditions and is a problem seen mostly among plants. A third difficulty for the biological species method of classification involves hermaphrodites where the idea of a closed gene pool holds no meaning. Continuing with the closed gene pool idea is the existence of chronospecies which simply relates to the different stages of evolution of the same species over the passage of time.

The great range of biological diversity found throughout the globe is a product of the divergence of species that express actualization of the biological species concept.

Our Galaxy Could Include Numerous Earth-Like Planets That Harbor Life

Clara Moskowitz writing in the WIRED SCIENCE BLOG explains that:"Earth-like planets may in fact be common in the galaxy, increasing the likelihood of extraterrestrial life." The key to making such a claim has come from the observation of "the remains of smashed up asteroids around dead stars" that revealed that the "chemical composition" of the residue "resembles the materials inside Earth and the other small, rocky inner planets of our solar system." This optimistic news was revealed at the American Astronomical Society by Michael Jura, an astronomer from UCLA who stated: "We found evidence that this asteroid dust is similar to rocks on Earth,.. This strengthens suspicions that Earth-like planets are common." Jura went on to say: "Asteroids are leftover building blocks that didn’t get incorporated into the planets,.. What we have now is a tool to measure the bulk composition of planets." Moskowitz further detailed the significance of the underlying connection between: "Asteroids and planets (which) are made from the same stuff: the dusty material that circles around young stars in disks. Eventually some of the dust clumps together and grows into planets, while asteroids represent the detritus left over. Because asteroids are formed from the same material as planets, observing asteroids around other stars can tell us crucial information about what ingredients are available to form planets around those stars." The NASA Spitzer Space Telescope was utilized by Jura and a team of experts: "to observe six dead white-dwarf stars that were coated with the debris of shredded asteroids that had collided into them. By viewing the stars through a spectrograph, which separates out light from different wavelengths, the scientists were able to observe the telltale signatures of certain chemicals in the light. Since that starlight is passing through the film of the asteroid debris, the light picked up signatures of the asteroids’ composition, too. The team found that the asteroid dust contains a glassy silicate mineral similar to minerals commonly found on Earth. They also detected a lack of carbon in the dust, which again echoes the solar system’s rocky planets and asteroids, which also have no carbon." Astronomers have made the discovery of Earth-like planets a priority because they believe that is where there may exist "the likeliest place for extraterrestrial life." In Jura's opinion, the search for "asteroid debris around dead stars" provides the most promising possibility for understanding planet formation and he and his fellow observers will continue their search for stars surrounded by asteroid dust and debris.