Jun 232014

New Research Casts Doubt on the Late Heavy Bombardment

Was the early solar system bombarded with lots of big impacts? This is a question that has puzzled scientists for over 35 years. And it not just an academic one. We know from rocks on Earth that life began to evolve very early on, at least 3.8 billion years ago. If the Earth was being pummeled by large impacts at this time, this would certainly have affected the evolution of canada goose jacket uk life. So, did the solar system go through what is known as the Late Heavy Bombardment (LHB)? Exciting new research, using data from the Lunar Reconnaissance Orbiter Camera (LROC) may cast some doubt on the popular LHB theory.

canada goose coats on sale It actually quite a heated debate, one that has polarized the science community for quite some time. In canada goose outlet buffalo one camp are those that believe the solar system experienced a cataclysm of large impacts about 3.8 billion years ago. In the other camp are those that think such impacts were spread more evenly over the time of the early solar system from approximately 4.3 to 3.8 billion years ago. canada goose coats on sale

The controversy revolves around two large impact basins, which are found fairly close to each other on the Moon. The Imbrium basin canada goose outlet uk is one of the youngest basins on the canada goose outlet black friday near side of the Moon, while the Serenetatis basin is thought to be one of the oldest. Both canada goose outlet hong canada goose outlet kong are flooded with volcanic basalts and are big enough to be seen from Earth with the naked eye.

canada goose coats Scientists know the relative ages of such lunar basins because of a concept called superposition. Basically, superposition states that what is on top must be younger than what is beneath. Using such relationships, scientists can determine which basins are older and which are younger. canada goose coats

To get an canada goose outlet in vancouver absolute age, though, scientists need actual bits of rock, so they can use canada goose outlet price radiometric dating techniques. The lunar samples returned by the Apollo program provided exactly that. But, the Apollo samples suggest that the Imbrium and Serenitatis basins are barely 50 million years apart.

canada goose clearance Relative age dating tells us there are over 30 other basins that formed within that time frame. This means that roughly one major impact canada goose outlet belgium occurred every 1.5 million years! Now, 1.5 million years may sound like a long time. But consider the last large impact that happened on Earth, the Chicxulub event 65 million years ago, which is thought to have exterminated the dinosaurs. Imagine another 40 dinosaur killing impacts occurring since then. It would be surprising if any life survived such a barrage! canada goose clearance

Canada Goose Outlet This is why a team of researchers, led by Dr. Paul Spudis of the Lunar and Planetary Institute, is looking very carefully at this question. Their research is using the principle of superposition to show that several of the areas visited by the Apollo program were blanketed by material from the Imbrium impact. This could mean that canada goose outlet montreal many of the collected Apollo materials may be sampling the same event. Canada Goose Outlet

canada goose clearance sale Dr. Spudis research focuses on the Montes Taurus area, between the Serenitatis and Crisium basins, not far from the Apollo 17 landing site. This is a region dominated by sculpted hills that have been interpreted to be ejected material from the adjacent Serenitatis basin impact. But, Dr. Spudis and his team have found that, instead, this sculpted material comes from the Imbrium basin some 600 kilometers away. Furthermore, the grooves and lineated features of this terrain point to the Imbrium basin, not the Serenitatis basin, and line up with similar features in the Alpes and Fra Mauro Formations, which are known to be ejecta from the Imbrium impact. In the north of Serenitatis, these Imbrium formations even seem to transform into the Montes Taurus, confirming that the sculpted hills do, in fact, originate from the Imbrium impact. canada goose clearance sale

Recent high quality data from the Lunar Reconnaissance Orbiter Camera shows that the sculpted terrain, which is present at the Apollo 17 landing site, is related to material that is known to be from the Imbruim impact. This means that Apollo 17 may have sampled Imbrium and not Serenitatis material. This could explain the unusually close ages of these two basins, suggested by the Apollo samples. If so, the Serenitatis impact may have occurred much earlier than previously thought, meaning that a barrage of frequent bombardments did not occur, and life on Earth could have evolved without being molested by too many impact events.

Canada Goose Parka Image credit: NASA/GSFC/Arizona State University Canada Goose Parka

Click on the image to explore the LROC data in greater detail.

If the sculpted hills are Imbruim ejecta, then it is possible that Apollo 17 sampled Imbrium and not Serenitatis materials. That casts suspicion on the very close radiometric ages of these two basins. Perhaps these ages are so close because we effectively measured the same material. In that case, the age of Serenitatis could be much older than the 3.87 billion years the Apollo 17 samples suggest. If true, this would mean that there was canada goose parka outlet no Late Heavy Bombardment at the time life was forming on the early Earth, leaving life to evolve with relatively few impact related interruptions.

Spudis et al., 2011, Journal of Geophysical Research, V116, E00H03

canadian goose jacket W00t! canada goose outlet mall Universe Today starts the new year with canada goose outlet reviews a canada goose outlet germany big bang. canadian goose jacket

Canada Goose canada goose sale uk sale This interests me a lot as an astrobiology student, so with all due respect to the discipline of planetary geology I am going to take this in two passes. The astrobiology first: Canada Goose sale

If the Earth was being pummeled by large impacts at this time, this would certainly have affected the evolution of life.

Yes, whether or not the Late Heavy Bombardment (LHB) happened is important in many hypotheses, from aspects of supplementing Earth volatile supply over when life arose to the effects it had on first life.

canada goose black friday sale First it must be noted that people assumed for a very long time that the LHB would be difficult to survive for life at all. Even https://www.canadagoosestorevip.com more so the first simple non robust cells would respond slower and less to environmental change, having fewer traits in the first place. canada goose black friday sale

buy canada goose jacket However when people recently started to model what would happen, it was immediately canada goose shop uk apparent that LHB is survivable. canada goose outlet shop Cells proliferate and spread faster than any reasonable impact ratio can keep up local sterilization. buy canada goose jacket

buy canada goose jacket cheap analysis shows that there is no plausible situation in which the habitable zone canada goose coats uk was fully sterilized on Earth, at least since the termination of primary accretion of the planets and the postulated impact origin of the Moon. buy canada goose jacket cheap

canada goose Later models takes a today populated Goldilock survival zone 1 km down the crust into account, in which case crust busters momentarily vaporizing the oceans would be survivable. canada goose

canada goose store Assuming that cellular life can survive the LHB what would be the ramifications? Abramov Mojzsis notes that even mesophiles can survive, but that thermophiles would have the advantage. Hence they suggest that evolutionary deep thermophily, remains of which are shared over all three moder domains by ancestry, would be predicted. canada goose store

The existence of deep traits and specifically thermophily is itself another heated debate.

canada goose deals My personal impression is that a) suggested RNA/DNA base pair preference and protein fold thermometers have canada goose outlet eu problems, and b) so called long branch attraction clustering non related organisms as the phylogenetic signal becomes weak makes deep history of specific genes difficult to ascertain. However gene family data seem to suggest a root of mesophily, with canada goose factory outlet vancouver later evolved thermophily. canada goose deals

Canada Goose online Similarly it appears from gene family methods that UCA cells were much as complex as modern cells at the time of the LHB. What happened after the LHB was that there was a great diversification as cells learned to exploit electron transport redox processes and hence many new ecological niches. (Basically they evolved modern photosynthesis and a more efficient ATP generation using membrane potentials.) Canada Goose online

cheap Canada Goose You can predict the LHB from phylogenetics canada goose outlet online store and fossils, but the current record is suggestive. On the other hand if it didn happen it doesn affect what we know, but perhaps the preparedness of accepting early life in the Hadean. cheap Canada Goose

Canada Goose Jackets But consider the last large impact that happened on Earth, the Chicxulub event 65 million years ago, which canada goose parka outlet uk is thought to have exterminated the dinosaurs. Imagine another 40 dinosaur killing impacts occurring since then. It would be surprising if any life survived such a barrage Canada Goose Jackets.

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