Announcement

Collapse

Natural Science 301 Guidelines

This is an open forum area for all members for discussions on all issues of science and origins. This area will and does get volatile at times, but we ask that it be kept to a dull roar, and moderators will intervene to keep the peace if necessary. This means obvious trolling and flaming that becomes a problem will be dealt with, and you might find yourself in the doghouse.

As usual, Tweb rules apply. If you haven't read them now would be a good time.

Forum Rules: Here
See more
See less

New fossils push back the indisputable origin of life

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • rogue06
    replied
    Originally posted by lee_merrill View Post
    But can you demonstrate that that would be enough time for photosynthetic life to evolve?

    Blessings,
    Lee
    If Mojzsis is correct we're looking at a space of over 700 million years. Let's say he seriously miscalculated and was off by 200 million years. That's still 500 million or half of a billion years. To put another way, during the Cambrian, not long after the Burgess Shale formation was laid down. And look how much has changed over that period of time.

    While it is true that most of the phyla that are around today arose during the Cambrian (some like sponges, annelids and cnidarians arose earlier in the Precambrian[1]) they are not anything like what we see today. Back in the Cambrian there were no amphibians, reptiles, birds, or mammals (much less humans). Simply put there were hardly any chordates at all, to say nothing of vertebrates. As far as fish go, they were limited to primitive, invertebrate jawless creatures that one can classify as "fish" like Haikouichthys, but no fully developed modern fish. Fish like we commonly find today are nowhere to be found in Cambrian deposits.

    And there were few if any terrestrial insects (which represent well over 50% of all animal life currently existing on the planet).

    Flora-wise there were not only any flowering plants (angiosperms) there weren't even any gymnosperms from which they arose from. There wasn't much in the way of any sort of terrestrial plants at all (vascular plants first arose during the Silurian long after end of the Cambrian).

    As Graham Budd and Sören Jensen noted in their 2000 paper, A critical reappraisal of the fossil record of the bilaterian phyla, Cambrian life was still unlike almost anything that we observe today. While a number of phyla appear to have diverged in the Early Cambrian or earlier, most of the phylum-level body plans first appear in the fossil record much later on.

    This flies in the face of the oft repeated claim made by creationists that, as Jonathan Wells (Senior Fellow at the Discovery Institute) puts it, "Most animal forms appear in the form they currently have in the present." Nope. Not even remotely close.

    Secondly, the type of photosynthesis that first arose was likely very different than what we think of now. For instance, from a decade and a half ago, but I don't think it is obsolete, the abstract from Photosynthesis in the Archean Era

    Abstract

    The earliest reductant for photosynthesis may have been H2. The carbon isotope composition measured in graphite from the 3.8-Ga Isua Supercrustal Belt in Greenland is attributed to H2-driven photosynthesis, rather than to oxygenic photosynthesis as there would have been no evolutionary pressure for oxygenic photosynthesis in the presence of H2. Anoxygenic photosynthesis may also be responsible for the filamentous mats found in the 3.4-Ga Buck Reef Chert in South Africa. Another early reductant was probably H2S. Eventually the supply of H2 in the atmosphere was likely to have been attenuated by the production of CH4 by methanogens, and the supply of H2S was likely to have been restricted to special environments near volcanos. Evaporites, possible stromatolites, and possible microfossils found in the 3.5-Ga Warrawoona Megasequence in Australia are attributed to sulfur-driven photosynthesis. Proteobacteria and protocyanobacteria are assumed to have evolved to use ferrous iron as reductant sometime around 3.0 Ga or earlier. This type of photosynthesis could have produced banded iron formations similar to those produced by oxygenic photosynthesis. Microfossils, stromatolites, and chemical biomarkers in Australia and South Africa show that cyanobacteria containing chlorophyll a and carrying out oxygenic photosynthesis appeared by 2.8 Ga, but the oxygen level in the atmosphere did not begin to increase until about 2.3 Ga.


    Still, to be honest, I really don't know how long it all would take to evolve, but given the above considerations, the amount of time that may have been available from the origin of life to some type of photosynthesis doesn't seem unreasonable. Look at for instance what conservative estimates are for how long it would take eyes to have evolved[2]







    1. And at least one phyla arose after the Cambrian. Bryozoa, for instance, is not known before the early Ordovician.

    2. Back in 1994 Dan-Erik Nilsson and Susanne Pelger worked out a mathematical model on the time needed for a patch of light sensitive cells or photoreceptors covered by a layer of transparent tissue to evolve into a lensed eye resembling those commonly seen in many fish was reached. They found that it would take roughly 364,000 generations -- which equates to less than half a million years.

    It took roughly 400 steps for the photoreceptor layer and pigment layer to form a retinal pit which continued to deepen until after approximately 1000 steps until it formed into a pin-hole camera eye. After this the lens shape continued evolving and the iris flattened allowing better focusing thereby providing improved optical properties.

    In the end they found that the complete evolution of an eye like those found in a vertebrate or octopus took less than 2000 steps.

    Moreover, Nilsson and Pelger took great pains to deliberately choose very conservative (low), pessimistic assumptions in their calculations so in reality it probably would have taken much less time to take place. For instance, they assumed that for every 101 organisms that got a certain mutation which provided them improved vision that 100 without this improvement also survived. This assumes that you are essentially as well off without the improvement in vision as you are with it which, in the real word, is extremely unlikely.

    For those actually interested the paper can be found here: A pessimistic estimate of the time required for an eye to evolve

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    The article in Nature would say otherwise:

    [cite=Nature]A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).
    You were not clear. I believe your post indicated the time needed for abiogenesis to take place and life to begin, and not using the genetic clock to date the time life began. If this is the case you answered your own question estimates based on the genetic clock roughly agree with the geologic evidence when life began.

    The geologic data demonstrates that what is described as the last part of the Hadean has the conditions suitable for life: sea floor spreading, continents forming and sedimentary rocks based on the presence of the zircon crystals and carbon deposits.

    [quote=lee_merrill] What about the genetic molecular clock estimates? Putting the origin of life back in the Hadean. The earliest fossils were photosynthetic, which is complex life, and would require some development.

    The answer is simple; the right environmental conditions for abiogenesis to take place would the requirement for some development to take place. A molecular clock is not what defines the beginning of life through abiogenesis. The molecular clock estimates are to estimate when abiogenesis took place.
    Last edited by shunyadragon; 07-16-2021, 08:40 PM.

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by rogue06 View Post
    That's still a gap of hundreds of millions of years. That's a lot of time for something to happen.
    But can you demonstrate that that would be enough time for photosynthetic life to evolve?

    Blessings,
    Lee

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by shunyadragon View Post
    There are no genetic clock estimates for abiogenesis just your nonscientific pseudo math ENRON Creationist probability foolishness.
    The article in Nature would say otherwise:

    Source: Nature

    A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).

    Source

    © Copyright Original Source



    Life began when the conditions were right for life to begin. Abiogenesis like evolution is environmentally driven.
    But if life began early after conditions were right, that might not allow time for life to develop.

    Blessings,
    Lee

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    Interesting, that would certainly provide more time for life to develop. But then there is this:

    Source: Wikipedia

    More recently, a similar study of Jack Hills rocks shows traces of the same sort of potential organic indicators. Thorsten Geisler of the Institute for Mineralogy at the University of Münster studied traces of carbon trapped in small pieces of diamond and graphite within zircons dating to 4.25 Ga. The ratio of carbon-12 to carbon-13 was unusually high, normally a sign of "processing" by life.

    Source

    © Copyright Original Source


    Blessings,
    Lee
    Recent studies?!?! This has been known for 40-50 years. A brief footnote in Wikipedia is not good source.

    Leave a comment:


  • rogue06
    replied
    Originally posted by lee_merrill View Post
    Interesting, that would certainly provide more time for life to develop. But then there is this:

    Source: Wikipedia

    More recently, a similar study of Jack Hills rocks shows traces of the same sort of potential organic indicators. Thorsten Geisler of the Institute for Mineralogy at the University of Münster studied traces of carbon trapped in small pieces of diamond and graphite within zircons dating to 4.25 Ga. The ratio of carbon-12 to carbon-13 was unusually high, normally a sign of "processing" by life.

    Source

    © Copyright Original Source


    Blessings,
    Lee
    That's still a gap of hundreds of millions of years. That's a lot of time for something to happen.

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    What about the genetic molecular clock estimates? Putting the origin of life back in the Hadean. The earliest fossils were photosynthetic, which is complex life, and would require some development.

    Blessings,
    Lee
    Revised response:

    There are no genetic clock estimates for abiogenesis just your nonscientific pseudo math ENRON Creationist probability foolishness.

    Again, life did possibly begin back in the late Hadean, but it would have been when sedimentary rocks and continents began to form. Life began when continents began to form, oceans existed, sedimentary rocks, and sea floor spreading began in the beginning of the Archean, which defines the beginning of the Archean.

    Your reference provided evidence for establishing a new date for the beginning of the Archean The estimates of dares have always been an estimate you know (~). Some are subdividing the late Hadean with presence of carbon and zircon crystals in the strata more like the Archean. Actually this is nothing new.

    Source: https://en.wikipedia.org/wiki/Hadean



    In the last decades of the 20th-century geologists identified a few Hadean rocks from western Greenland, northwestern Canada, and Western Australia. In 2015, traces of carbon minerals interpreted as "remains of biotic life" were found in 4.1-billion-year-old rocks in Western Australia.[10][11]

    The oldest dated zircon crystals, enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia, date to 4.404 ± 0.008 Ga.[12] This zircon is a slight outlier, with the oldest consistently-dated zircon falling closer to 4.35 Ga[12]—around 200 million years after the hypothesized time of the Earth's formation.

    In many other areas, xenocryst (or relict) Hadean zircons enclosed in older rocks indicate that younger rocks have formed on older terranes and have incorporated some of the older material. One example occurs in the Guiana shield from the Iwokrama Formation of southern Guyana where zircon cores have been dated at 4.22 Ga.[

    © Copyright Original Source



    Again, again and again for abiogenesis there is absolutely no genetic clock estimates for abiogenesis except for your imagination. Life began when the conditions were right for life to begin. Abiogenesis like evolution is environmentally driven.
    Last edited by shunyadragon; 07-13-2021, 05:55 PM.

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    What about the genetic molecular clock estimates? Putting the origin of life back in the Hadean. The earliest fossils were photosynthetic, which is complex life, and would require some development.

    Blessings,
    Lee
    There are no genetic clock estimates just your nonscientific pseudo math ENRON Creationist probability foolishness.

    Again, life did not begin back in the Hadean, At least get that through your thick scull. There are no known rock formations in the HAdean. Life began when continents began to form, oceans existed, sedimentary rocks, and sea floor spreading began in the beginning of the Archean, which defines the beginning of the Archean.

    Your reference provided evidence for establishing a new date for the beginning of the Archean The estimates of dares have always been an estimate you know (~).
    Last edited by shunyadragon; 07-13-2021, 05:38 PM.

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by shunyadragon View Post
    The geologic evidence speaks for itself. Life began and persisted throughout the Archean and Proterozoic despite the comet and meteorite bombardment.
    What about the genetic molecular clock estimates? Putting the origin of life back in the Hadean. The earliest fossils were photosynthetic, which is complex life, and would require some development.

    Blessings,
    Lee

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by rogue06 View Post
    Two relatively recent articles to chew on dealing with the whole idea of a Late Heavy Bombardment and when it might have taken place...
    Interesting, that would certainly provide more time for life to develop. But then there is this:

    Source: Wikipedia

    More recently, a similar study of Jack Hills rocks shows traces of the same sort of potential organic indicators. Thorsten Geisler of the Institute for Mineralogy at the University of Münster studied traces of carbon trapped in small pieces of diamond and graphite within zircons dating to 4.25 Ga. The ratio of carbon-12 to carbon-13 was unusually high, normally a sign of "processing" by life.

    Source

    © Copyright Original Source


    Blessings,
    Lee

    Leave a comment:


  • rogue06
    replied
    Two relatively recent articles to chew on dealing with the whole idea of a Late Heavy Bombardment and when it might have taken place:

    Source: Bashing holes in the tale of Earth’s troubled youth


    New analyses undermine a popular theory about an intense asteroid storm 4 billion years ago.



    Early in Earth’s history, roughly half a billion years after the planet formed, all hell broke loose in the inner Solar System. A barrage of asteroids — some the size of Hong Kong — pummelled the globe intensely enough to melt large parts of its surface. This incendiary spree around 4 billion years ago vaporized most of Earth’s water and perhaps even sterilized its exterior, killing off any life that might have started to emerge. Only after this storm of impacts passed did the planet become safe enough for hardy organisms to take firm root and eventually give rise to all later life.

    That horrific episode, known as the Late Heavy Bombardment (LHB), has been an integral part of Earth’s origin story for decades, ever since geologists did a systematic study of samples brought back from the Moon by NASA Apollo missions. But now, the once-popular theory has come under attack, and mounting evidence is causing many researchers to abandon it. A growing community of planetary scientists thinks that things quietened down relatively quickly, with a steadily decreasing rain of asteroids that ended a few hundred million years after Earth and the Moon formed.

    Settling the debate could have major ramifications for some of the biggest questions in geoscience: when did life emerge and what were conditions like on early Earth? But some researchers think that fresh samples will be needed to finally put this conundrum to rest. They are looking with hope at the United States’ recent pledge to send astronauts back to the Moon — although no timeline has yet been set. In the meantime, the community is grappling with the fact that a key chapter of Solar System history might be vanishing before their eyes.

    “The Late Heavy Bombardment was seen as one of the great triumphs of the Apollo era,” says geochemist Mark Harrison of the University of California, Los Angeles. “There’s no question that something has happened in the past few years that has profoundly upset the apple cart.”

    The Solar System formed some 4.6 billion years ago, after the centre of a massive cloud of gas and dust collapsed into a dense sphere that became our Sun. Pebbles in a dusty disk orbiting the star continuously collided and sometimes stuck together. After tens of millions of years, these agglomerations had built up into planetesimals — the beginnings of the planets. Other rocky fragments remained, crashing into their larger kin and leaving deep craters. Over time, the Solar System thinned out, leaving something like the configuration we see today.

    Most of the evidence of this violent history has been erased on Earth by the churning of tectonic plates. But the scarred surface of the Moon, long inert, retains a lengthy record of impacts. Some of that record — roughly 382 kilograms of lunar rock and soil — was collected by Apollo astronauts and carried back to scientists eager to see what the samples might reveal about the Moon’s history. In 1973, the year after the last Apollo landing, a group at Sheffield University, UK, reported a curious pattern in samples from four separate Apollo missions as well as a Soviet Luna mission. Radiometric dating of each one returned the same age: 3.95 billion years1. A team at the California Institute of Technology (Caltech) in Pasadena corroborated the findings the same year2.

    Curious chronology

    The confluence of ages suggested that a flurry of objects struck the Moon in a narrow 50-million-year window, leaving behind countless impact craters — including as many as a dozen of the Texas-sized basins that scar the surface. Because it seemed to represent a final surge of pandemonium after the Solar System’s chaotic genesis, the Caltech team named the event the terminal lunar cataclysm, although it later became more popularly known as the LHB.

    The idea was immediately divisive, in large part because of ambiguity in the rock dating. This was done primarily by measuring the rocks’ ratio of argon-40 atoms to radioactive potassium-40. 40K decays into 40Ar with a half-life of 1.25 billion years. At high temperatures, that 40Ar can leak out of minerals. That makes the ratio of these two isotopes a kind of clock: the more time that has elapsed since a rock was hot, the more 40Ar should be present. But making sense of the argon and potassium concentrations can be difficult because the same ratio could have been caused by a concentrated barrage that heated the rocks and released 40Ar some 3.95 billion years ago, or by a long, dwindling asteroid torrent that released it in fits and starts before fizzling out at about the same time.

    The first really new data arrived in 2000. Planetary scientist David Kring, cosmochemist Timothy Swindle and planetary scientist Barbara Cohen, all then at the University of Arizona in Tucson, collected lunar meteorites that had fallen to Earth after being blasted from the Moon’s surface by asteroid strikes. They hoped such rocks would provide a more random sample of the Moon’s crust than those from Apollo, which represent at most 4% of the lunar surface. But when the results came back, they showed a curious, and familiar, pattern.

    “Frankly, I thought we’d measure a bunch of these and have ages running back to 4.3 and 4.4 [billion years] and prove once and for all that this whole idea was wrong,” says Swindle. Instead, they found no evidence of impacts before the hypothesized time of the LHB3. “That kind of pushed me to a different side of the fence,” he says.

    But researchers still wondered how a bombardment could come so long after the Solar System formed. By the half-billion-year mark, most of the leftover debris should either have been cast out or have settled into stable zones such as the main asteroid belt, which sits between Mars and Jupiter, or the Kuiper belt beyond Neptune. Nobody could come up with a physical reason for the unexpected drama at such a late date. “Where did you have the bodies in the Solar System that could hang around for 600 million years and then come screaming in and hit the Moon?” asks Cohen, who is now at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    A potential answer arrived in 2005, with the emergence of what came to be known as the Nice model, after the French city where it was conceived. Originally proposed to explain odd orbital behaviour by distant icy objects in the Kuiper belt, the conjecture asserted that the Solar System’s outer planets had formed much closer to one another than they are now. Computer simulations showed4 how the massive gravitational pull of Jupiter and Saturn could have created an instability that ultimately bumped Uranus and Neptune into more distant orbits, knocked comets out of remote reservoirs and kicked asteroids out of the main belt.

    The Nice model offered huge support for the LHB. “I think this helped cement this idea,” says physicist Nicolle Zellner of Albion College in Michigan. Geologist Marc Norman of the Australian National University in Canberra agrees. “That was the next real turning point,” he says.

    Cataclysmic confusion

    Yet just when the idea of the LHB finally seemed unimpeachable, holes began to appear. Apollo data and ‘crater counting’, which estimates the order in which craters were laid down on the basis of how they overlap, had indicated that three of the largest crater basins on the Moon’s near side — Imbrium, Nectaris and Serenitatis — might all be about 3.95 billion years old (see ‘Sampling the Moon’). But high-resolution maps from NASA’s Lunar Reconnaissance Orbiter, which started circling the Moon in 2009, spotted rays of debris extending from Imbrium5. This suggested that the impact that formed the crater might have knocked rocks into nearby Serenitatis, contaminating the Apollo samples picked up there. In 2010, a reanalysis of rocks thought to have been ejected from Nectaris indicated that they were also chemically and geologically similar to Imbrium material6. “We started realizing that maybe we were sampling Imbrium over and over,” says Zellner.

    Clickenate on imagification
    d41586-018-01074-6_15407032.jpg
    to enbiggenate




    The data from lunar meteorites didn’t necessarily help. Although none of the samples seemed to be older than 4 billion years, some were billions of years younger than that3, with no obvious spike around 3.95 billion years. And the Apollo samples held other surprises. Since 2012, detailed study7 of microscopic regions in the rocks has turned up ages of as much as 4.2 billion years, much older than any seen before, suggesting that there had been significant impacts earlier than the proposed spike.

    Prodded in part by these revelations, some researchers proposed8 a longer-lasting LHB that began around 4.1 billion or 4.2 billion years ago. But that idea had one major strike against it: some of the most ancient crystals on Earth, from the Jack Hills range in Australia, suggest9 that the planet was a fairly clement place then, with relatively low temperatures and ample water.

    Hot topic

    Others are still scrutinizing the original Apollo evidence. To determine the samples’ ages, researchers heated the rocks to release argon, slowly ramping up the temperature. But as far back as 1991, Harrison had pointed out that the process won’t work well for rocks containing multiple minerals. Different minerals will release their argon at different temperatures. A sample heated to 400 °C might provide an age of 2 billion years; to 500 °C, an age of 2.5 billion. Researchers have tried to extrapolate from this behaviour, but Harrison says the complex patterns often lead them to pick essentially arbitrary ages. “This is quackery,” he says. “There’s no physical basis for it.”

    Swindle says the argon heating situation is not necessarily as bad as Harrison makes it out to be; Apollo samples can be found whose ages don’t change significantly with temperature, and their dates — whether they refer to one or multiple impacts — still cluster around 3.95 billion years. Cohen says that other chronometers, such as those using radioactive isotopes of rubidium and uranium, corroborate the argon ages (although Harrison counters that the dates can differ by as much as 600 million years).

    Such back and forth underscores how difficult it can be to tease small clues out of extremely ancient rocks. “Sherlock Holmes was good at resolving mysteries that happened last year,” says David Nesvornı, a planetary scientist at the Southwest Research Institute in Boulder, Colorado. “This all happened 4 billion years ago.”

    Meanwhile, the Nice model has proved less helpful to the idea of an LHB than it once seemed. More-advanced simulations of the early Solar System’s gravitational interactions indicate that the planetary reshuffling probably happened shortly after formation, not with a delay of hundreds of millions of years10. Nesvornı likens delaying the reshuffling — and so keeping the Solar System hovering on the edge of instability — to trying to balance a pencil on its tip. “It’s really hard to put the pencil there in such a way that it falls in an hour,” he says.

    One of the original architects of the Nice model, astronomer Alessandro Morbidelli of the Cote d’Azur Observatory in Nice, admits that the first versions took fine-tuning to get the reshuffling to occur so late. He no longer believes in the LHB, and sees many others in the field trading in the idea of a sudden asteroid deluge for that of a long, declining tail of bombardment. “My prediction is people will abandon the cataclysm,” he says.

    Even those who remain tied to the LHB have had to modify their ideas. Planetary scientist William Bottke of the Southwest Research Institute agrees that there is no longer much support for a single, short spike. He says the best reading of the evidence, including samples from ancient Earth and radiometric dates in meteorite rocks, is a more drawn-out surge of bombardment that began around 4.1 billion or 4 billion years ago, with a relative lull before that, consistent with the existence of surface water in that period.

    Astronomer William Hartmann, a visiting scientist at the International Space Science Institute in Bern, thinks the current situation proves that the idea of a cataclysm was never particularly robust. Various research communities “kind of had the impression that the other community had really solved this”, he says. “A paradigm structure was built up from supporting evidence, none of which was actually conclusive in itself.”

    If an LHB did not happen, that could make it easier to explain how life emerged. Evidence of microbial life has been found in rocks that are around 3.5 billion years old. But those fossils seem quite complex, suggesting that they had been evolving from earlier forms for at least a few hundred million years, during the originally hypothesized time of the LHB. Without the cataclysm, such an ancient genesis might make more sense. Then again, some evidence suggests that the microbes at the base of the tree of life were hyperthermophiles — that is, organisms that thrived in extreme heat. The intense conditions created by a rain of asteroids could have resulted in a number of pockets where life might have emerged.

    So far, efforts to clinch the LHB debate with evidence from other likely victims — Mercury, Venus, Mars and objects from the asteroid belt — have proved inconclusive. Each camp accuses the other of cherry-picking favourable data and not looking at the total picture. “It’s a Rorschach test,” says Norman. “People see what they want to see and disregard the rest.”

    The only thing that researchers say will substantially move the needle is new samples from the Moon. Kring, now at the Lunar and Planetary Institute in Houston, Texas, has developed some concepts for sample-return missions, including one that would see astronauts collecting rocks from the South Pole–Aitken basin, the largest and oldest impact crater on the Moon. However, the next human mission to the Moon is still a long way off. The first new lunar rocks to be carried back to Earth may come from China’s Chang’e-5, a robotic mission currently planned for 2019. It aims to collect samples from the volcanic Mons Rümker formation, an area younger than those explored by Apollo astronauts.

    Although no single exploration effort is likely to end the dispute, researchers’ improved understanding of the Moon and how to determine the ages of samples should provide greater confidence in the results.

    However things eventually shake out, the new evidence will shift careers and rewrite textbooks. Yet, perhaps because of the long-lived nature of this debate, those trying to make sense of the LHB remain flexible, sceptical and surprisingly lighthearted.

    “We are close friends and therefore we disagree all the time and then go drink a beer together,” says Bottke. “One should carry models lightly and be prepared to drop them if something better comes along, because it happens all the time.”


    Source

    © Copyright Original Source



    and

    Source: New date for 'Late Heavy Bombardment' may change life's timeline on Earth


    Our planet may have been last pummeled by asteroid impacts longer ago than previously thought, explaining why life began to form almost 4 billion years ago.

    The solar system once experienced a meteor shower of epic proportions: Asteroids whizzed around the inner planets, crashing down in a rain of fire that left their surfaces scarred for billions of years. Astronomers typically call this period the Late Heavy Bombardment.

    But exactly when that fiery assault happened has been a matter of intense debate. The answer has big implications for the evolution of the solar system as a whole, and even for the timeline of life on Earth.

    Finding evidence of such a bombardment here on Earth is difficult. Our planet regularly melts and recycles its crust, destroying detailed evidence that might give us a concrete age for the period of heavy meteor impacts. Farther off, on Mercury, Mars, and the rocky or icy moons of the outer solar system, scientists are left to count craters, an imprecise dating method. The other option is to use an objective dating method – radiometric rock dating, for instance – on bodies that have kept cleaner records than Earth. The Moon and asteroids – or the meteorite pieces of them that fall to Earth – are the most accessible.

    When astronauts first brought back samples of the Moon, 50 years ago this summer, scientists found that they all showed evidence of massive and intense impacts at about 3.9 billion years ago. Later lunar missions returned more samples, and all agreed: some disaster occurred on the Moon that indicated a massive slew of impacts less than 4 billion years ago. For decades, scientists sought to explain what might have caused a sudden influx of asteroids and comets into the inner solar system.

    But more recent evidence has hinted that Earth might have had liquid surface water before this period. It’s hard to reconcile how our planet maintained a surface cool enough to host water while undergoing a massive cataclysm. And dates from meteorites never agreed with the 3.9 billion-years-ago date from lunar rocks.

    Now, astronomers led by Stephen Mojzsis from the University of Colorado, Boulder, have shown that the bombardment may have happened much earlier: 4.48 billion years ago. That would leave plenty of time for Earth to cool and life to emerge. They published their findings August 12 in the Astrophysical Journal.

    Resetting the Clock

    Most researchers think the Late Heavy Bombardment was caused by the giant planets moving around, orbiting closer to and farther from the sun and pushing lots of smaller solar system objects like asteroids along with them. But Mojzsis points out that there’s no timeline inherently attached to such a reshuffling.

    “So look to the asteroid belt,” Mojzsis suggests. “The asteroids predate the planets, by definition. And we have 60,000 meteorites from the asteroids.”

    His study, he says, is the first to consider the ages of all those meteorites on Earth. “And we find no uptick at 3.9 billion,” the time of the proposed Late Heavy Bombardment, he says. But his team did see that most of the rocks had been “reset” — basically melted to such an extent that it restarts the radiometric clocks researchers use to figure out a rock’s age. That melting is a sign of massive impacts, and they found the clocks reset at 4.48 billion years ago, only 80 million years after the start of the solar system. “The best explanation is that’s when giant planet migration occurred,” Mojzsis says.

    Instead of one big spike, this earlier period of asteroid bombardment would have been a slow tapering-off from the early days when the solar system was little more than rocks crashing into each other. In Mojzsis’ timeline, the giant planets still migrated, but much earlier than previous theories suggested. This means there was no giant spike of meteors, but rather a flux of incoming asteroids that blended into the general chaos of the young solar system.

    The best – and only real – argument for a more recent spike of impactors comes from lunar samples, which do show signs of some cataclysm occurring 3.9 billion years ago.

    But, as Mojzsis explains, “If you look at the bombardment record from craters from Mercury, the Moon, Mars, satellites of the outer solar system, none of them show an uptick in bombardment. It’s only the lunar samples, which were all collected and returned to the Earth from a small patch of the Moon, just some 12 percent of the lunar surface, and all collected near Mare Imbrium [Crater].”

    That geographical clustering, more than anything else, hurts the reliability of the lunar samples. It’s clear something catastrophic happened in the Mare Imbrium area, but it’s not as obvious that it must have been a Moon-wide — let alone solar system-wide — event.

    If NASA – or any of the other actors in the increasingly crowded race back to the Moon – succeeds in visiting the Moon’s more remote South Pole-Aitkin Basin and returning samples from that oldest known crater, it would “complete the puzzle,” according to Mojzsis.

    But in the meantime, he thinks his results lay to rest the idea of a Late Heavy Bombardment. Instead, Mojzsis prefers a history where the influx of asteroids and comets slowly wound down from the solar system’s wild earlier days to a gentle drift of space dust and the occasional stray impactor that still occurs today.

    Letting Life Flourish

    Mojzsis’ work doesn’t only depend on measuring meteorite ages. Because there’s a lot of evidence for a migration of giant planets, Mojzsis’ team modeled what it would look like if the event had happened early enough to explain the 4.48 billion years ago date he saw in the meteorites.

    “We dynamically modeled what we’d analyzed geochemically. If this is correct, can this predict the reset ages we see on the Earth, Moon, and Mars? And it does. At 4.48 [billion years ago],” he says.

    And that in turn pushes back the age of a hospitable Earth. If space more or less ceased pelting our planet with asteroids by 4.48 billion years ago, that allows the Earth to cool and form water. The oldest rocks scientists have found on Earth come from zircons, and these indicate Earth had water some 4 billion years ago. The first hints of life appear at 3.8 billion to 3.9 billion years ago, an age hard to reconcile with the idea of a massive meteor bombardment happening at the same time.

    Earth would have still suffered the occasional asteroid blow – we see them even today, and we have strong evidence that one killed off the dinosaurs. But Mojzsis’ work means that Earth wouldn’t have suffered the kind of strikes that would boil away entire oceans and liquefy the whole surface more recently than 4.48 billion years ago.

    “I think this resolves the conversation,” Mojzsis says of his work.



    Source

    © Copyright Original Source



    The full paper for the latter, Onset of Giant Planet Migration before 4480 Million Years Ago is available by clicking on the hyperlink provided, although here is the abstract from it

    Abstract

    Soon after their formation, the terrestrial planets experienced intense impact bombardment by comets, leftover planetesimals from primary accretion, and asteroids. This temporal interval in solar system evolution, termed late accretion, thermally and chemically modified solid planetary surfaces and may have impeded life's emergence on the Hadean (pre-3850 Ma) Earth. The sources and tempo of bombardment, however, remain obscure. Here we present a timeline that relates variably retentive radiometric ages documented from asteroidal meteorites to new dynamical models that invoke an early episode of planetesimal-driven giant planet migration after the dispersal of the protoplanetary disk. Reconciliation of geochronological data with dynamical models shows that such giant planet migration should lead to an intense ~30 Myr influx of comets to the entire solar system manifested in radiometric age data. The absence of wholesale crustal reset ages after ~4450 Ma for the most resilient chronometers from Earth, Moon, Mars, 4 Vesta, and various meteorite parent bodies confines the onset of giant planet migration to ca. 4480 Ma. Waning impacts continue to strike the inner planets through a protracted monotonic decline in impactor flux, in agreement with predictions from crater chronology. New global 3D thermal analytical bombardment models derived from our revised impact mass-production functions show also that persistent niches for prebiotic chemistry leading to the emergence of life on the early Hadean Earth could endure late accretion since at least about 4400 million years ago.

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    So the earliest fossils are at 3.7 billion years ago, and the late heavy bombardment (LHB) was at 3.8 billion years ago. The LHB has been considered a sterilization event, if this is correct, that leaves only 100 million years for life to originate. Not much time! Which is why I would expect people to want to put the origin of life back in the Hadean era, along with (as was mentioned) genetic molecular clock estimates.

    Blessings,
    Lee
    The geologic evidence speaks for itself. Life began and persisted throughout the Archean and Proterozoic despite the comet and meteorite bombardment. The fact that the environment necessary for the beginning of life existed and the evidence of life exists is enough to justify that life began regardless of your hypothetical limits on time frame. The research you cited simply pushed back the beginning of life and the beginning of the Archean. ~0.2 billion years, and the beginning of the Archean. So what? Please not the (~) in these estimates of dates.

    The evidence in history of life on earth is that both abiogenesis and evolution is environmentally driven.
    Last edited by shunyadragon; 07-12-2021, 06:47 PM.

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by shunyadragon View Post
    Let's go with the evidence of what is found in the Archean. There is evidence of bacterial life in the beginning of the Archain, given a range of ~.2 billion years one way or the other). Therefore there was no complete oblideration of the beginning of life.in the early Archean. This research just pushes back the beginning date of the Archean. The bottomline is there are no known rocks dating to the Hadean.
    So the earliest fossils are at 3.7 billion years ago, and the late heavy bombardment (LHB) was at 3.8 billion years ago. The LHB has been considered a sterilization event, if this is correct, that leaves only 100 million years for life to originate. Not much time! Which is why I would expect people to want to put the origin of life back in the Hadean era, along with (as was mentioned) genetic molecular clock estimates.

    Blessings,
    Lee

    Leave a comment:


  • lee_merrill
    replied
    Originally posted by rogue06 View Post
    Cosmic impacts take place at sea as well.
    Certainly, which would make the origin of life in the sea more difficult too. Though I'm not sure what point you're making here...

    Blessings,
    Lee

    Leave a comment:


  • shunyadragon
    replied
    Originally posted by lee_merrill View Post
    Well, they say now that the origin of life probably happened in the Hadean era:

    Source: Nature

    A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).

    © Copyright Original Source


    So the origin of life would probably be in the oceans (near smokers?), where the large quantity of water would tend to dilute any reactions.

    Source: Reasons to Believe

    Yet the latest discovery by the Australian scientists doesn’t fit this scenario. The Isua stromatolites formed at the earth’s surface in a shallow water environment. In fact, the research team generated data that effectively ruled out stromatolite formation near hydrothermal vents. But if the refugium model has validity, the Isua fossils should have formed in a high-temperature milieu.

    Source

    © Copyright Original Source


    Also, we may note that reducing the timeframe for the origin of life by 220 million years doesn't leave much time for the origin of life! And having life originate in the Hadean era is going to be more difficult.

    Blessings,
    Lee
    Let's go with the evidence of what is found in the Archean. There is evidence of bacterial life in the beginning of the Archain, given a range of ~.2 billion years one way or the other). Therefore there was no complete oblideration of the beginning of life.in the early Archean. This research just pushes back the beginning date of the Archean. The bottomline is there are no known rocks dating to the Hadean.

    The various meteorite bombbardments occured throughout the Archean and Proterozoic. Nonetheless fossil evidence of life is found throughout this period.

    Source: https://ucmp.berkeley.edu/precambrian/archean_hadean.php


    The Archean Eon and the Hadean

    The Archean eon, which preceded the Proterozoic eon, spanned about 1.5 billion years and is subdivided into four eras: the Neoarchean (2.8 to 2.5 billion years ago), Mesoarchean (3.2 to 2.8 billion years ago), Paleoarchean (3.6 to 3.2 billion years ago), and Eoarchean (4 to 3.6 billion years ago).*

    If you were able to travel back to visit the Earth during the Archean, you would likely not recognize it as the same planet we inhabit today. The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.

    It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archean was bacterial. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites. Stromatolites have been found as fossils in early Archean rocks of South Africa and western Australia. Stromatolites increased in abundance throughout the Archean, but began to decline during the Proterozoic. They are not common today, but they are doing well in Shark Bay,

    The Hadean

    Hadean time (4.6 to 4 billion years ago)* is not a geological period as such. No rocks on the Earth are this old, except for meteorites. During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The relative abundance of heavier elements in the Solar System suggests that this gas and dust was derived from a supernova, or supernovas — the explosion of an old, massive star. Heavier elements are generated within stars by nuclear fusion of hydrogen, and are otherwise uncommon. We can see similar processes taking place today in so-called diffuse nebulae in this and other galaxies, such as the Nebula M16, below left.

    The sun formed within such a cloud of gas and dust, shrinking in on itself by gravitational compaction until it began to undergo nuclear fusion and give off light and heat. Surrounding particles began to coalesce by gravity into larger lumps, or planetesimals, which continued to aggregate into planets. "Left-over" material formed asteroids and comets, like asteroid Ida, above right.

    Because collisions between large planetesimals release a lot of heat, the Earth and other planets would have been molten at the beginning of their histories. Solidification of the molten material into rock happened as the Earth cooled. The oldest meteorites and lunar rocks are about 4.5 billion years old, but the oldest Earth rocks currently known are 3.8 billion years. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid. Once solid rock formed on the Earth, its geological history began. This most likely happened prior to 3.8 billion years, but hard evidence for this is lacking. Erosion and plate tectonics has probably destroyed all of the solid rocks that were older than 3.8 billion years. The advent of a rock record roughly marks the beginning of the Archean eon.

    © Copyright Original Source



    The timing of the beginning of life in the Archean is not definitely established, but nonetheless the beginning of the Archean, given .2 billion years one way or the other is the beginning of the possibility of life beginning when the continents began forming, sedimentary rocks appeared, and evidence of oceans and mid-ocean ridges formed.
    Last edited by shunyadragon; 07-12-2021, 05:14 PM.

    Leave a comment:

Related Threads

Collapse

Topics Statistics Last Post
Started by rogue06, Yesterday, 10:59 AM
10 responses
40 views
0 likes
Last Post Sparko
by Sparko
 
Started by rogue06, 12-02-2021, 09:14 AM
1 response
23 views
0 likes
Last Post shunyadragon  
Started by Roy, 12-02-2021, 06:58 AM
15 responses
110 views
0 likes
Last Post Markus River  
Started by rogue06, 12-01-2021, 08:26 AM
25 responses
110 views
0 likes
Last Post Ronson
by Ronson
 
Started by lee_merrill, 11-30-2021, 08:03 PM
27 responses
117 views
0 likes
Last Post rogue06
by rogue06
 
Working...
X