How did life on Earth begin? An giant step toward solving this puzzle was taken in the 1980's with the Nobel Prize–winning discovery by Tom Cech and Sidney Altman that RNA, the sister molecule of DNA, can catalyze certain chemical reactions inside cells, a job previously thought to be the exclusive domain of proteins. Until their discovery, RNA was thought to have just one function: storing the genetic information cells need to build proteins. This new revelation about RNA's dual role suggested to some scientists, including Harvard's Jack Szostak, that RNA likely existed long before DNA or proteins because it might be able to catalyze its own reproduction. Their discovery made it easier to think about how life began, Szostak says. RNA --Does It Harbor a Clue to the Origin of Life on Earth?
"Entire Solar Systems are Needed to Kick-Start Life" (A 2013 Most Popular) There is evidence that life on Earth could not have started without the other planets. The conditions on the prehistoric Earth would only have served to inhibit the formation of RNA. Mars, on the other hand, would have been just right. While there was some water on ancient Mars, there wouldn't have been enough to hamper the formation of RNA. Also, while the early Earth was starved of oxygen, Mars would have had enough to create oxidized molybdenum and boron, which are pivotal in the construction of RNA. Autogenic forms are probably more widespread than life in the Universe as they can be constructed from many different materials.
DNA stores the information of life, proteins provide the action, and in between sits elusive RNA, which serves both as a database of information and as a molecular machine. In the 1980's Walter Gilbert of Harvard coined the term RNA World, a primitive version of life on Early Earth that used RNA as both a catalyst and carrier of genetic information, which later evolved into a more efficent version in which DNA stored genetic information and proteins became the primary catalysts. RNA is more flexible than DNA, and its three-dimensional structures are more complex than proteins. MIT Zooms in on 3-D Enigmas of RNA --"Not Obeying Rules of Thermodynamics in Living Cells"
“When the Earth formed some 4.5 billion years ago, it was a sterile planet inhospitable to living organisms,” said Sankar Chatterjee, Horn Professor of Geosciences and curator of paleontology at the Museum of Texas Tech University. “It was a seething cauldron of erupting volcanoes, raining meteors and hot, noxious gasses. One billion years later, it was a placid, watery planet teeming with microbial life – the ancestors to all living things.” “For may years, the debate on the origins of life centered on the chemical evolution of living cells from organic molecules by natural processes. Chatterjee said life began in four steps of increasing complexity – cosmic, geological, chemical and biological. By studying three sites containing the world’s oldest fossils, he believes he knows how the first single-celled organisms formed in hydrothermal crater basins. "How Did Life Begin on Earth?" --A New Theory Embraces the Cosmic through Geological, Chemical, and Biological Stages
Meteorite Contains Extraterrestrial Organic Molecules Never Found Before Meteorite hunters found fragments of the rock, identified by the "fusion crust" that forms when it burns in the atmosphere. NASA and the SETI Institute in Mountain View, California, also mobilised a search team of about 30 scientists to search for the small black rocks. The meteorite turned out to be a very rare type of rock called CM chondrite, which makes up less than 1 per cent of the meteorites that fall to Earth. According to Bill Cooke of NASA's Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Alabama, it is not clear whether it is rare because it easily burns up in the atmosphere or there are just fewer of these rocks in space. The meteorite has now led to an important discovery concerning the possible inventory of molecules available to the early Earth.
“The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock,” says Steven Benner of the Westheimer Institute for Science and Technology. “It’s lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life. If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell. Minerals Essential for Life on Earth Came from Mars --New Evidence
If there is life on Mars, it’s not too farfetched to believe that such Martian species may share genetic roots with life on Earth, based on RNA or DNA because more than 3.5 billion years ago, a blitz of meteors ricocheted around the solar system, passing material between the two fledgling planets. This may have left bits of Earth on Mars, and vice versa, creating a shared genetic ancestry between the two planets. Chris McKay, a planetary scientist with the Space Science Division of NASA’s Ames Research Center, says a radiation-resilient DNA-sequencing chip is a promising candidate for future life-detecting missions to Mars and other planets. This search is the focus for Christopher Carr, a research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences, who's building a DNA sequencer that he hopes will one day be sent to Mars, where it can analyze soil and ice samples for traces of DNA and other genetic material. Searching for DNA on Mars & Beyond --New MIT Chip for Future Life-Detecting Missions
Comet Impacts on Early Earth Catalyst for Building Blocks for Life Early Earth was not very hospitable when it came to jump starting life. In fact, new research shows that life on Earth may have come from out of this world. Lawrence Livermore scientist Nir Goldman and University of Ontario Institute of Technology colleague Isaac Tamblyn (a former LLNL postdoc) found that icy comets that crashed into Earth billions of years ago could have produced life building organic compounds, including the building blocks of proteins and nucleobases pairs of DNA and RNA . Comets contain a variety of simple molecules, such as water, ammonia, methanol and carbon dioxide, and an impact event with a planetary surface would provide an abundant supply of energy to drive chemical reactions. "The flux of organic matter to Earth via comets and asteroids during periods of heavy bombardment may have been as high as 10 trillion kilograms per year, delivering up to several orders of magnitude greater mass of organics than what likely pre-existed on the planet," Goldman said.
An important discovery answers one of the key questions for scientist trying to unlock the processes that gave rise to early life forms : Why don’t we see new life forms today? New research explains how the reactive phosphorus that was an essential component for creating the earliest life forms came to Earth. The scientists found that during the Hadean and Archean eons – the first of the four principal eons of the Earth’s earliest history – the heavy bombardment of meteorites provided reactive phosphorus that when released in water could be incorporated into prebiotic molecules. The scientists documented the phosphorus in early Archean limestone, showing it was abundant some 3.5 billion years ago. "Why Don’t We See New Life Forms Today?" --New Research Provides Clue
“Stromatolites were one of the earliest examples of the intimate connection between biology—living things—and geology—the structure of the Earth itself,” said Woods Hole Oceanographic Institution (WHOI) geobiologist Joan Bernhard, lead author of the study. The growing bacterial community secreted sticky compounds that bound the sediment grains around themselves, creating a mineral “microfabric” that accumulated to become massive formations. Stromatolites dominated the scene for more than two billion years, until late in the Proterozoic Eon. “Then, around 1 billion years ago, their diversity and their fossil abundance begin to take a nosedive,” said Bernhard. Disappearance of the Earliest Manifestation of Life on Earth --Solved!
Orion Molecular Cloud --"A Source of the Complex Building Blocks of Life" The spectacular new image above shows just a part of a bigger complex called the Orion Molecular Cloud, in the constellation of Orion (The Hunter). A rich melting pot of bright nebulae, hot young stars and cold dust clouds, this region is hundreds of light-years across and located about 1350 light-years from us. The orange glow represents faint light coming from grains of cold interstellar dust , at wavelengths too long for human eyes to see.
A Spectacular Interstellar Cloud --The Thermonuclear Engines of Star Creation The Danish 1.54-metre telescope located at ESO’s La Silla Observatory in Chile has captured a striking image of NGC 6559, a cloud of gas and dust located at a distance of about 5000 light-years from Earth, showcasing the anarchy that reigns when stars form inside an interstellar cloud. The glowing region is a relatively small object, just a few light-years across, in contrast to the one hundred light-years and more spanned by its famous neighbor, the Lagoon Nebula (Messier 8, eso0936). Although it is usually overlooked in favor of its distinguished companion, NGC 6559 has the leading role in this new picture. The gas in the clouds of NGC 6559, mainly hydrogen, is the raw material for star formation. When a region inside this nebula gathers enough matter, it starts to collapse under its own gravity. The center of the cloud grows ever denser and hotter, until thermonuclear fusion begins and a star is born.
The most fertile bursts of star birth in the early Universe took place in distant galaxies containing lots of cosmic dust. These galaxies are of key importance to our understanding of galaxy formation and evolution over the history of the Universe, but the dust obscures them and makes them difficult to identify with visible-light telescopes. To pick them out, astronomers must use telescopes that observe light at longer wavelengths, around one millimetre, such as ALMA. But, in the APEX images, each burst of star formation appeared as a relatively fuzzy blob, which may be so broad that it covered more than one galaxy in sharper images made at other wavelengths. Without knowing exactly which of the galaxies are forming the stars, astronomers were hampered in their study of star formation in the early Universe. Pinpointing the correct galaxies requires sharper observations, and sharper observations require a bigger telescope. Most Prolific Star-Forming Galaxies of the Early Universe Detected by New Atacama Desert Large Array
"Scientists previously thought that as we got closer to the surface of Titan, the moon's atmospheric chemistry was basically inert and dull," said Murthy Gudipati, the paper's lead author at JPL. "Our experiment shows that's not true. The same kind of light that drives biological chemistry on Earth's surface could also drive chemistry on Titan, even though Titan receives far less light from the sun and is much colder. Titan is not a sleeping giant in the lower atmosphere, but at least half awake in its chemical activity." "Titan's Atmosphere Points to Building Blocks of Life" --NASA Astrobiology
Many biologists still view RNA as a messenger to shutlle inforamtion from DNA to the cell's protein manufacturing centers, ribosomes. Like DNA, RNA is a string of four different kinds of nucleotide building blocks, except that RNA has a single chain rather than DNA's iconic double helix that uses a different sugar in its molecular architecture, and substitutes uracil instead of thymine. However, unlike DNA, RNA is capable of carrying both genetic information and getting metabolic work done making it the "" molecule capabable of both reproducing itself and carrying the code to guide the needed copying. Some bacterial cells can swim, morph into new forms and even become dangerously virulent - all without initial involvement of DNA. RNA --"DNA's Messenger or the Origin of Life on Earth?" (Weekend Feature)
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