New Research Casts Doubt on the Late Heavy Bombardment

27 Replies to “New Research Casts Doubt on the Late Heavy Bombardment”

1. “Basically, superposition states that what is on top must be older than what’s underneath.”

   This is backwards. Superposition states that what is on top must beyounger than what is beneath.

   1. And here I was trying to figure out what I was missing after reading that, and coming to the conclusion that I must be slightly more logically inept than I thought.

   2. I was in WTF mode staring at that, wondering how that could be. If that’s indeed backwards, could Dr. Antonenko or someone please fix it?

   3. Thank you so much Joseph Yates for catching that! I can’t believe I missed it.

   4. Forgive me if you fixed already but I think you had a copy and paste moment :

      “Basically, superposition states that what is what is on top must be younger than what is beneath.”

      ie, what is x2

      1. It was indeed fixed, thanks to his post:).

   5. That’s what she said.

2. You have both sides of the argument having the LHB ending approx 3.8 bya. Other researchers feel that the bombardment may have been spread even further and lasted as long as to 2.4 bya. http://youtu.be/4MMYTzb0L_s

   1. As I added to my comment, I forgot to check the updated thread before posting a similar reference after yours. My apologies! Great minds and all that, I suppose.

3. W00t! Universe Today starts the new year with a big bang.

   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:

   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.

   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 more so the first simple non-robust cells would respond slower and less to environmental change, having fewer traits in the first place.

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

   “Our analysis shows that there is no plausible situation in which the habitable zone was fully sterilized on Earth, at least since the termination of primary accretion of the planets and the postulated impact origin of the Moon.”

   Life is a plague on a planet.

   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.

   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.

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

   My personal impression is that a) suggested RNA/DNA base pair preference and protein fold thermometers have 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 later evolved thermophily.

   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.)

   You can’t predict the LHB from phylogenetics and fossils, but the current record is suggestive. On the other hand if it didn’t happen it doesn’t affect what we know, but perhaps the preparedness of accepting early life in the Hadean.

   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!

   Well, no, not surprising as I suggested above.

   And the problem with extrapolating from the Chicxulub impactor is obvious. It is the only impact event more or less accepted as causing a mass extinction.

   That it did so in modern times should raise an alarm.

   I don’t know if it is definitive, but this review by Schulte et al is impressive. They do tie the K-Pg extinction to the impactor. And more importantly here they point out that the extinction was caused by an unlucky happenstance impact in calciferous and sulfurous sediments. (IIRC the details, I don’t have access as I write this.)

   Such sediments are only laid down, in patches, in modern times of an oxygenated atmosphere by biosphere processes. Hence you can’t take such a one off event to extrapolate general impact effects today. And even less so in the Hadean where we may or may not have had life.

4. I actually don’t care what people believe.
   I want to see evidence and facts.
   I have no doubt to change camps if the evidence leads over there.

   1. Yes, so we must send men back to the Moon, or *very* capable robotic rovers. Lets have some of the far side this time, too.

5. It’s actually quite a heated debate, one that has polarized the science community for quite some time.

   It’s something like this. 😉

   .

6. Good stuff, Torbjorn.

   Let me guess what happened. Why not? 😀 From 4.5 billion years ago big boulders had continually been falling on planets till 3.8 billion years ago. 😀 And they keep falling till now, but not so much. Pluto is not a planet and LHB didn’t happen. 😀 It was ECB, early continual bombardment. 😀 Give me Nobel prize. :d

   1. Thank you!

      Well, the dating issues and the recent dynamics is exciting. A few years ago, it was all “~ 3.8 Ga bp and then the rock record disappears”.

      Now there are implications on everything from early water, organics and tectonics (from zircons) to early crust and mantle compositions and dating (various rocks & isotope ratios) to early life (the changing and argued fossil record & gene family histories).

      And the Moon is both a player and a bench sitter with records on some of these things. I honestly thinks it adds to the romance of the “night light” when I see it.

7. And, a little more sheepishly seeing the length of the first comment and the subject of planetary geology, on to the latter:

   I don’t have access to Spudis et al, but I think this is a work in a series that criticizes the Apollo 17 samples. That is all good and well, but there are much more things up in the air that may or may not problematize datings on the Moon:

   – As reported here on Universe Today: Moon volatile content is now on par with the Earth’s which supports a Earth-Moon impactor. While at the same time the datings of crustal FAN rocks may rewrite early lunar history.

   – The Moon nearside/farside dichotomy has solutions affecting the dating record of the Moon. A late impactor on the farside may renewed it and transferred material to the nearside.

   – The LHB is, I think, in evidence on other bodies from Mercury to Earth.

   – LHB datings in general seems to be a problem. I vaguely remembered works on “a late, late Earth tail of LHB but I didn’t know that the work had grown:

   “The Late Heavy Bombardment (LHB) is often described as an impact spike on the Moon and terrestrial planets that was triggered by giant planet migration ~4 Gy ago (Ga). The comets and main belt asteroids scattered by this event, however, were probably too limited in number to reproduce ancient lunar crater populations. Here we show that many LHB projectiles came from the E-belt, a hypothesized extension of the main belt between 1.7-2.1 AU. Destabilized by giant planet migration, this belt produced ~10 of the Moon’s youngest basins between 3.7-4.1 Ga. Assuming 2-3 additional basins come from the main belt population, we predict the LHB consisted of 12-13 lunar basins. This places the twelfth youngest basin Nectaris near the start of the LHB at ~4,1 Ga, a result consistent with both crater and (limited) sample constraints.

   An unexpected attribute of the E-belt is that it makes a long-lived tail of impactors; we predict it formed ~60 and ~4 Chicxulub-sized or larger craters on the Earth and Moon between 1.7-3.7 Ga, respectively. This matches the number of large lunar craters found on Late Imbrian terrains (3 from 3.2-3.7 Ga) and Eratostenian terrains (1 on 1.5-3.2 Ga). Interestingly, our work also reproduces Earth’s distribution of Archean-era impact spherule beds. with 7, 4, 1, and 0 spherule beds identified in 3.23-3.47, 2.49-2.63, 1.7-2.1, and 0.6-1.7 Ga outcrops. We conclude that major LHB impacts ended on Earth much later than on the Moon, and that the ~1.85 and ~2 Gy old terrestrial craters Sudbury and Vredefort probably represent the last gasp of the LHB on Earth.” [My bold.]

   This claim of course ties in with the Abramov et al on LHB survivability.

   Btw, it would be interesting to hear more about the latter work and how people see it and the putative evidence of a late LHB tail. Especially the difference in LHB tailing on different impacted bodies could warrant some detailing.

8. And, a little more sheepishly seeing the length of the first comment and the subject of planetary geology, on to the latter:

   I don’t have access to Spudis et al, but I think this is a work in a series that criticizes the Apollo 17 samples. That is all good and well, but there are much more things up in the air that may or may not problematize datings on the Moon:

   – As reported here on Universe Today: Moon volatile content is now on par with the Earth’s which supports a Earth-Moon impactor. While at the same time the datings of crustal FAN rocks may rewrite early lunar history.

   – The Moon nearside/farside dichotomy has solutions affecting the dating record of the Moon. A late impactor on the farside may renewed it and transferred material to the nearside.

   – The LHB is, I think, in evidence on other bodies from Mercury to Earth.

   – LHB datings in general seems to be a problem. I vaguely remembered works on “a late, late Earth tail of LHB but I didn’t know that the work had grown:

   “The Late Heavy Bombardment (LHB) is often described as an impact spike on the Moon and terrestrial planets that was triggered by giant planet migration ~4 Gy ago (Ga). The comets and main belt asteroids scattered by this event, however, were probably too limited in number to reproduce ancient lunar crater populations. Here we show that many LHB projectiles came from the E-belt, a hypothesized extension of the main belt between 1.7-2.1 AU. Destabilized by giant planet migration, this belt produced ~10 of the Moon’s youngest basins between 3.7-4.1 Ga. Assuming 2-3 additional basins come from the main belt population, we predict the LHB consisted of 12-13 lunar basins. This places the twelfth youngest basin Nectaris near the start of the LHB at ~4,1 Ga, a result consistent with both crater and (limited) sample constraints.

   An unexpected attribute of the E-belt is that it makes a long-lived tail of impactors; we predict it formed ~60 and ~4 Chicxulub-sized or larger craters on the Earth and Moon between 1.7-3.7 Ga, respectively. This matches the number of large lunar craters found on Late Imbrian terrains (3 from 3.2-3.7 Ga) and Eratostenian terrains (1 on 1.5-3.2 Ga). Interestingly, our work also reproduces Earth’s distribution of Archean-era impact spherule beds. with 7, 4, 1, and 0 spherule beds identified in 3.23-3.47, 2.49-2.63, 1.7-2.1, and 0.6-1.7 Ga outcrops. We conclude that major LHB impacts ended on Earth much later than on the Moon, and that the ~1.85 and ~2 Gy old terrestrial craters Sudbury and Vredefort probably represent the last gasp of the LHB on Earth.” [My bold.]

   This claim of course ties in with the Abramov et al on LHB survivability.

   Btw, it would be interesting to hear more about the latter work and how people see it and the putative evidence of a late LHB tail. Especially the difference in LHB tailing on different impacted bodies could warrant some detailing.

9. “In one camp are those that believe the solar system experienced a cataclysm of large impacts about 3.8 billion years ago.”

   ( As one holding to an alternate view of star-planet creation, I find this very interesting in context. Where else is supposed evidence, clearly engraved or subtly etched, for one model actually camouflaged proof of another, either overlooked, or actually readable – but misinterpreted? )
   ____________________________________________________________________________

   If I understand the revision born in this new insight ( not a surprising to me ), there was ONE massive bombardment episode – or “cataclysm” – which stroke the Solar System in the distant past.

   In a different frame of view, this would be a sudden storm-front emergence, breaking-out and encompassing the Sun’s entire realm in its fury, heavily impacting all its planetary members, and attendants. ( The Asteroids and Comets being the debris PRODUCED in wake of its passage – not the leftover precipitation from its formation: WRECKAGE of completed order, rather than leftover building material. )

   ONE tempest event that wrecked wide-spread havoc on the Sun’s worlds, once pristine in celestial dawn existence – an early genesis time of beautifully ordered morning creation, alive with promise, and filled with hope of life’s-animating touch ( where ocean surf could be heard on Venus, and the lapping sounds of lake-water on Mars ).

   Now, of course, we see worlds displaying all manner of howling desolation, cast-open to the darkness of space, or buried under smothering gloom of heavy-pressing cloud-decks, locked in extremes of steel-cracking cold, or fiercely imprisoned in lead-melting heat, if not frozen-down in orbital time under blue Neptune’s trident, or lost-out through decay of years in a Martian desert: ruined surfaces exposed to the fierce vacuum of space, bathed in radiation showers, unscreened.

   All along, one oasis world teeming with life, Planet Earth, has given bold testimony against this concept of multiple bombardment hail-storms. It is quite enough of a “miracle” that life could emerge, or rebound, just ONCE – and that spontaneously – from global catastrophic fallout of terrible consequences from bombardment. But multiple times through ages unseen?

   1. I think this merit some comment.

      The astrobiology first:

      – We have to distinguish between rebound, which in turn can be repopulation and/or diversification, and emergence. Here we are mostly discussing repopulation as I commented on below. Gene family data makes clear that diversification happened later.

      – What actually happened during LHB if Abramov et al are correct is not a global repopulation but a process of local exponential population growth such as in a petri dish. A recently sterilized area was an excellent locale for invading cells as there was little competition in the beginning.

      And chemical evolution theories notes that impactors supply both energy and organics, quite likely making the locale improved relative to before. Some suggest abiogenesis _happened_ after an impact.

      – I believe the molecular biologist Monod is mostly responsible for the idea of abiogenesis as a “chance” coincidence. However it is, when you think about it, an untestable just so story. Moreover it doesn’t make any sense whatsoever in the light of modern statistical process theory of stationary processes!

      In such a “chance” picture a dynamical system looks like a vast phase space which have just an exceedingly small volume of abiogenesis where all the conditions are “just so”. And all (or enough) of a vast space was explored “just so” by the process and its environment before that volume was encountered.

      However I can’t see how that translates to a stochastic process, except that at the surface it looks like the exact opposite of “stationary”!

      If we treat abiogenesis as a stationary enough process of repeated attempts of chemical evolution to proceed to biological evolution, it will simplest look like a Poisson process. Then the short delay until abiogenesis (at most ~ 0.2 normed delay, ~ 1 Ga out of ~ 5 Ga) translates to a deterministically simple and/or rapidly repeating process.

      In any case, something that can be modeled by a stochastic process, such as chemical evolution, is not a random coincidence. That makes it both in principle quantifiable and a lot more likely for the average process.

      – If a late Earth-Moon impactor is correct, it is thus quite possible that it sterilized an earlier biosphere. In which case we would have to consider independent abiogenesis events. Maybe the Moon would have a record of that!

      The planetary science second:

      – The dating and composition places impactor material as originating with the planetary disk.

      They have gone to great lengths to find some interstellar dust particles in atmospheric and space samples of interplanetary dust particles. I don’t know if they ever have found an interstellar large body locally, but I would be interested to find out.

      – As the links to the “late LHB tail” references makes clear, you can also place the orbital parameters of impactors to interplanetary bodies.

      – Reversely, the reason why interstellar dust particles are rare, is because space is _vast_ and mostly _empty_. For an external bombardment you would need to pose not only a dense material approaching our own system but a vast extent to explain the long duration of the LHB.

      Much simpler to go with the data which suggest local origin. Relatedly, catastrophism has never made much of a splash after it started to be challenged by data as it is so unlikely in the first place.

      – “May not have been as far back as is commonly believed.”

      What are you, an YEC? That doesn’t work. I am reminded of the recent suggestion of the need for recalibration of the argon-argon clock dating the birth of the solar system. They have confirmed an earlier suggestion that there is a need for ~ 1.2 % adjustment at most.

      Which means the solar system may be ~ 4.50 Ga or ~ 4.60 Ga instead of ~ 4.54 Ga. But then it would bring the aim of ~ 0.1 % precision in sight, eventually dating the system to within +/- 1 Ma!

      [Wouldn’t it be fun if the solar system turns out to be 4.500 Ga old? =D]

      Which starts in on the last point of science:

      – “see these things through an alternate lens”.

      That doesn’t work either. I am sorry if it gets personal, but the topic is important in science.

      “The first principle is that you must not fool yourself, and you are the easiest person to fool.” [Feynman]

      To propose an idea that can be rejected by oneself more or less summarily from known data (see my first point on the planetary science aspect), is not to see things but to close one’s eyes and make up fantasy images. This would also be the case for untestable ideas.

      1. My apology, but much you wrote to respond to, and a 10-minute reply was insufficient for me, time was wanting, and thoughtful reply was needful.
         ___________________________________________________________________

         “The astrobiology first:” ______________________________

         I would say in simple response to this section of your reply, you can be as brilliant as Einstein, understand the finest-point workings of chemistry, or the cellular complexities of biology, and still be blind ( or you can be dense as a rock, and dull as a board, and be just as blind ).

         Well, I hope I am not a rock, heavy as some of your thoughts can be to decipher.

         My use of “rebound”, regarding the recuperation of a planets life, was not meant to be technically accurate, more figuratively used.

         I did understand your words about repopulation. My brush was a bit broad regarding “bombardments”. My piece was long enough as it was, without endless qualifications (not withstanding my need to improve writing skill!)

         You seem to subscribe to the prevailing “Theory” of life, and more broadly, all existence. And in that widely-held world view, life is no miracle, but common. So given innumerable planets, not a few must be alive with it, in sundry form, and of various stage of “evolutionary” development.

         This is based on the “hypothetical process by which living organisms [ can arise ] from nonliving matter” – Abiogenesis.

         Your comment lays-out a thicket of technical details. Some of which, is, frankly, beyond me.

         Well, you can dismiss me as a simpleton, but a LAW – real and demonstrable ( unlike the hypothetical ) – demolishes that supposed explanation of life’s origin. The Law of Biogenesis : “The principle that living organisms develop ONLY from other living organisms and NOT from nonliving matter. 2. Generation of living organisms from OTHER living organisms” (emphasis mine) – not inanimate matter, which is the distilled essence of any assertions, or speculations, however filled-in with speculative detail, or drawn-out over necessary time spans, that regard life origins from DEAD MATTER.

         Maybe relatively simple “chemical evolution” can occur, given a vast space filled with chance combinations of countless passing interactions-reactions. But if this can occur – given sufficient time and numbers – that rare sequence of just the right “start-up” assembly could not take the giant leap to a living organism. – Your “picture” of a “dynamical system [of] vast phase space…”?

         Life comes from LIFE (and the logical conclusion to that statement, I will leave to you) – that’s not fantasy, or wild imaginings, but real-world fact.

         First Cause, as opposed to rare chance moments of endless probabilities over vast oceans of time and space, or something like that?

         ( My point of view on things tends to project through a wide-field lens, yours, apparently, through a narrower, high-magnification one – full of fine-detail. Regarding both lenses: A man can fail to see the forest, for the trees; and, a man can fail to appreciate the trees for the forest. )
         ____

         “If a late Earth-Moon impactor is correct, it is thus quite possible that it sterilized an earlier biosphere. In which case we would have to consider independent abiogenesis events. Maybe the Moon would have a record of that!”
         ____

         Personal belief is not worth much, but basing it on something other than imagination, I firmly believe the Earths ancient biosphere (of which we have dramatic evidence on display in museums world-wide) was indeed “sterilized” by (you guessed it) – a cataclysm. But if Biogenesis is an active universal Law, then life emergence would have required a Life to regenerate a new biosphere – and a “terra-form” a wrecked world to welcome it. Earth would have been an uninhabitable waste, after the one Bombardment phase that I see – and visible through-out planetary space! (Another lens sees two, three…?)
         ____________________________________________________________________

         “The planetary science second:” ___________________________

         I can give you no counter “Science” off-hand to back this up, but I question the conclusion based on this dating of the “building material”, or debris (my view) coincident with the Solar System’s formation. Of course, if you buy into the collapsing nebula-rotating disk scenario, this is the output result you would tend to compute from given data.
         ____

         “Much simpler to go with the data which suggest local origin. Relatedly, catastrophism has never made much of a splash after it started to be challenged by data as it is so unlikely in the first place.”
         ____

         Curious statement, as Catastrophism is reawakening in the field of Geology. The Earth and Solar System bare the deep scars of at least one immense disaster (the fallout consequences of which could have rained down for who knows how long). I would assert, the “data” gives forceful testimony of widespread catastrophe (stripped of speculation and preconceptions).

         But then, again, was it the result of CONstruction, or the aftermath of DEstruction? Look at this through two different lenses. And everything will align-up with its perspective (and what does not will remain mysterious, or be summarily dismissed).

         [ A vivid picture just entered my mind from a WWI battle field scene: A “moonscape” of craters upon craters: where beautiful, pleasant order once stood, DESTRUCTION ensues from “heavy bombardment”; where once fields of green stood, through a storm of violence and war, they are turned into lifeless gray zone expanses of desolation. ]

         No, I am not a “YEC” (had to look that up). I accept the Universe could very well be billions of years old. So, no, I was not implying the barrage occurred 6,000 years ago. But, 65 million, 100m, … years ago, maybe. To put it simply, I do not accept it happened when the Solar System was built (by a cloud, or whatever).

         But, yes, my lens of view is outside the main-tube of the “scientific” community’s world-view (by no means all members thereof, but most, I would guess).
         ___

         “The first principle is that you must not fool yourself, and you are the easiest person to fool.” [Feynman]”

         Very true – and applicable to the lens-holders of both opposing mainstream views (with all their curious tributaries)!

         I did click the link, and find some of Mr. Richard Feynman’s quotes thought-provoking. ( I shall be reading through them. ) For example – – – >
         ___

         “To those who do not know mathematics it is difficult to get across a real feeling as to the beauty, the deepest beauty, of nature … If you want to learn about nature, to appreciate nature, it is necessary to understand the language that she speaks in.”

         I see profound insight there, though, alas, an interpreter I would need to grasp the depth of it. But, here too, something great is revealed.
         ___

         Torbjörn Larsson, on your closing point, there is data based on what is irrefutable (like predictable chemical reactions, or principles of nuclear fission/fusion; how and why the moon orbits, and phases in its revolutions…, etc.), and there is “data” based on hypothesis (unsubstantiated theory), with its naturally inclined interpretations and readings – or misinterpretations and misreadings (sincere as they may be).

         If you embrace that the Solar System DID come from a condensed Nebula – then, EVERYTHING you view (asteroids, comets, bombardments, even), study, or think about – in relation to that supposed event – will shade and color your speculations and conclusions – your whole approach: the draft picture you attempt to detail, in scientific quest to understand, will naturally form, take-shape, along the lines of evidence (real or alleged) – as they tend to fall-within (or match-up-to) that perspective point of view.

         There is a double-edged sword here: I think the “YEC”’s are likewise guilty of this.

         This mighty “bombardment” (one, or many? – may depend on one’s point of view), I saw as a case in point – one with really explosive impact.

   2. I think this merit some comment.

      The astrobiology first:

      – We have to distinguish between rebound, which in turn can be repopulation and/or diversification, and emergence. Here we are mostly discussing repopulation as I commented on below. Gene family data makes clear that diversification happened later.

      – What actually happened during LHB if Abramov et al are correct is not a global repopulation but a process of local exponential population growth such as in a petri dish. A recently sterilized area was an excellent locale for invading cells as there was little competition in the beginning.

      And chemical evolution theories notes that impactors supply both energy and organics, quite likely making the locale improved relative to before. Some suggest abiogenesis _happened_ after an impact.

      – I believe the molecular biologist Monod is mostly responsible for the idea of abiogenesis as a “chance” coincidence. However it is, when you think about it, an untestable just so story. Moreover it doesn’t make any sense whatsoever in the light of modern statistical process theory of stationary processes!

      In such a “chance” picture a dynamical system looks like a vast phase space which have just an exceedingly small volume of abiogenesis where all the conditions are “just so”. And all (or enough) of a vast space was explored “just so” by the process and its environment before that volume was encountered.

      However I can’t see how that translates to a stochastic process, except that at the surface it looks like the exact opposite of “stationary”!

      If we treat abiogenesis as a stationary enough process of repeated attempts of chemical evolution to proceed to biological evolution, it will simplest look like a Poisson process. Then the short delay until abiogenesis (at most ~ 0.2 normed delay, ~ 1 Ga out of ~ 5 Ga) translates to a deterministically simple and/or rapidly repeating process.

      In any case, something that can be modeled by a stochastic process, such as chemical evolution, is not a random coincidence. That makes it both in principle quantifiable and a lot more likely for the average process.

      – If a late Earth-Moon impactor is correct, it is thus quite possible that it sterilized an earlier biosphere. In which case we would have to consider independent abiogenesis events. Maybe the Moon would have a record of that!

      The planetary science second:

      – The dating and composition places impactor material as originating with the planetary disk.

      They have gone to great lengths to find some interstellar dust particles in atmospheric and space samples of interplanetary dust particles. I don’t know if they ever have found an interstellar large body locally, but I would be interested to find out.

      – As the links to the “late LHB tail” references makes clear, you can also place the orbital parameters of impactors to interplanetary bodies.

      – Reversely, the reason why interstellar dust particles are rare, is because space is _vast_ and mostly _empty_. For an external bombardment you would need to pose not only a dense material approaching our own system but a vast extent to explain the long duration of the LHB.

      Much simpler to go with the data which suggest local origin. Relatedly, catastrophism has never made much of a splash after it started to be challenged by data as it is so unlikely in the first place.

      – “May not have been as far back as is commonly believed.”

      What are you, an YEC? That doesn’t work. I am reminded of the recent suggestion of the need for recalibration of the argon-argon clock dating the birth of the solar system. They have confirmed an earlier suggestion that there is a need for ~ 1.2 % adjustment at most.

      Which means the solar system may be ~ 4.50 Ga or ~ 4.60 Ga instead of ~ 4.54 Ga. But then it would bring the aim of ~ 0.1 % precision in sight, eventually dating the system to within +/- 1 Ma!

      [Wouldn’t it be fun if the solar system turns out to be 4.500 Ga old? =D]

      Which starts in on the last point of science:

      – “see these things through an alternate lens”.

      That doesn’t work either. I am sorry if it gets personal, but the topic is important in science.

      “The first principle is that you must not fool yourself, and you are the easiest person to fool.” [Feynman]

      To propose an idea that can be rejected by oneself more or less summarily from known data (see my first point on the planetary science aspect), is not to see things but to close one’s eyes and make up fantasy images. This would also be the case for untestable ideas.

   3. I think this merit some comment.

      The astrobiology first:

      – We have to distinguish between rebound, which in turn can be repopulation and/or diversification, and emergence. Here we are mostly discussing repopulation as I commented on below. Gene family data makes clear that diversification happened later.

      – What actually happened during LHB if Abramov et al are correct is not a global repopulation but a process of local exponential population growth such as in a petri dish. A recently sterilized area was an excellent locale for invading cells as there was little competition in the beginning.

      And chemical evolution theories notes that impactors supply both energy and organics, quite likely making the locale improved relative to before. Some suggest abiogenesis _happened_ after an impact.

      – I believe the molecular biologist Monod is mostly responsible for the idea of abiogenesis as a “chance” coincidence. However it is, when you think about it, an untestable just so story. Moreover it doesn’t make any sense whatsoever in the light of modern statistical process theory of stationary processes!

      In such a “chance” picture a dynamical system looks like a vast phase space which have just an exceedingly small volume of abiogenesis where all the conditions are “just so”. And all (or enough) of a vast space was explored “just so” by the process and its environment before that volume was encountered.

      However I can’t see how that translates to a stochastic process, except that at the surface it looks like the exact opposite of “stationary”!

      If we treat abiogenesis as a stationary enough process of repeated attempts of chemical evolution to proceed to biological evolution, it will simplest look like a Poisson process. Then the short delay until abiogenesis (at most ~ 0.2 normed delay, ~ 1 Ga out of ~ 5 Ga) translates to a deterministically simple and/or rapidly repeating process.

      In any case, something that can be modeled by a stochastic process, such as chemical evolution, is not a random coincidence. That makes it both in principle quantifiable and a lot more likely for the average process.

      – If a late Earth-Moon impactor is correct, it is thus quite possible that it sterilized an earlier biosphere. In which case we would have to consider independent abiogenesis events. Maybe the Moon would have a record of that!

      The planetary science second:

      – The dating and composition places impactor material as originating with the planetary disk.

      They have gone to great lengths to find some interstellar dust particles in atmospheric and space samples of interplanetary dust particles. I don’t know if they ever have found an interstellar large body locally, but I would be interested to find out.

      – As the links to the “late LHB tail” references makes clear, you can also place the orbital parameters of impactors to interplanetary bodies.

      – Reversely, the reason why interstellar dust particles are rare, is because space is _vast_ and mostly _empty_. For an external bombardment you would need to pose not only a dense material approaching our own system but a vast extent to explain the long duration of the LHB.

      Much simpler to go with the data which suggest local origin. Relatedly, catastrophism has never made much of a splash after it started to be challenged by data as it is so unlikely in the first place.

      – “May not have been as far back as is commonly believed.”

      What are you, an YEC? That doesn’t work. I am reminded of the recent suggestion of the need for recalibration of the argon-argon clock dating the birth of the solar system. They have confirmed an earlier suggestion that there is a need for ~ 1.2 % adjustment at most.

      Which means the solar system may be ~ 4.50 Ga or ~ 4.60 Ga instead of ~ 4.54 Ga. But then it would bring the aim of ~ 0.1 % precision in sight, eventually dating the system to within +/- 1 Ma!

      [Wouldn’t it be fun if the solar system turns out to be 4.500 Ga old? =D]

      Which starts in on the last point of science:

      – “see these things through an alternate lens”.

      That doesn’t work either. I am sorry if it gets personal, but the topic is important in science.

      “The first principle is that you must not fool yourself, and you are the easiest person to fool.” [Feynman]

      To propose an idea that can be rejected by oneself more or less summarily from known data (see my first point on the planetary science aspect), is not to see things but to close one’s eyes and make up fantasy images. This would also be the case for untestable ideas.

   4. I think this merit some comment.

      The astrobiology first:

      – We have to distinguish between rebound, which in turn can be repopulation and/or diversification, and emergence. Here we are mostly discussing repopulation as I commented on below. Gene family data makes clear that diversification happened later.

      – What actually happened during LHB if Abramov et al are correct is not a global repopulation but a process of local exponential population growth such as in a petri dish. A recently sterilized area was an excellent locale for invading cells as there was little competition in the beginning.

      And chemical evolution theories notes that impactors supply both energy and organics, quite likely making the locale improved relative to before. Some suggest abiogenesis _happened_ after an impact.

      – I believe the molecular biologist Monod is mostly responsible for the idea of abiogenesis as a “chance” coincidence. However it is, when you think about it, an untestable just so story. Moreover it doesn’t make any sense whatsoever in the light of modern statistical process theory of stationary processes!

      In such a “chance” picture a dynamical system looks like a vast phase space which have just an exceedingly small volume of abiogenesis where all the conditions are “just so”. And all (or enough) of a vast space was explored “just so” by the process and its environment before that volume was encountered.

      However I can’t see how that translates to a stochastic process, except that at the surface it looks like the exact opposite of “stationary”!

      If we treat abiogenesis as a stationary enough process of repeated attempts of chemical evolution to proceed to biological evolution, it will simplest look like a Poisson process. Then the short delay until abiogenesis (at most ~ 0.2 normed delay, ~ 1 Ga out of ~ 5 Ga) translates to a deterministically simple and/or rapidly repeating process.

      In any case, something that can be modeled by a stochastic process, such as chemical evolution, is not a random coincidence. That makes it both in principle quantifiable and a lot more likely for the average process.

      – If a late Earth-Moon impactor is correct, it is thus quite possible that it sterilized an earlier biosphere. In which case we would have to consider independent abiogenesis events. Maybe the Moon would have a record of that!

      The planetary science second:

      – The dating and composition places impactor material as originating with the planetary disk.

      They have gone to great lengths to find some interstellar dust particles in atmospheric and space samples of interplanetary dust particles. I don’t know if they ever have found an interstellar large body locally, but I would be interested to find out.

      – As the links to the “late LHB tail” references makes clear, you can also place the orbital parameters of impactors to interplanetary bodies.

      – Reversely, the reason why interstellar dust particles are rare, is because space is _vast_ and mostly _empty_. For an external bombardment you would need to pose not only a dense material approaching our own system but a vast extent to explain the long duration of the LHB.

      Much simpler to go with the data which suggest local origin. Relatedly, catastrophism has never made much of a splash after it started to be challenged by data as it is so unlikely in the first place.

      – “May not have been as far back as is commonly believed.”

      What are you, an YEC? That doesn’t work. I am reminded of the recent suggestion of the need for recalibration of the argon-argon clock dating the birth of the solar system. They have confirmed an earlier suggestion that there is a need for ~ 1.2 % adjustment at most.

      Which means the solar system may be ~ 4.50 Ga or ~ 4.60 Ga instead of ~ 4.54 Ga. But then it would bring the aim of ~ 0.1 % precision in sight, eventually dating the system to within +/- 1 Ma!

      [Wouldn’t it be fun if the solar system turns out to be 4.500 Ga old? =D]

      Which starts in on the last point of science:

      – “see these things through an alternate lens”.

      That doesn’t work either. I am sorry if it gets personal, but the topic is important in science.

      “The first principle is that you must not fool yourself, and you are the easiest person to fool.” [Feynman]

      To propose an idea that can be rejected by oneself more or less summarily from known data (see my first point on the planetary science aspect), is not to see things but to close one’s eyes and make up fantasy images. This would also be the case for untestable ideas.

10. I thank Irene for her cogent and well written summary of our paper. I want to clarify a bit more precisely exactly what we concluded from our work.

    Our principal result is that the Sculptured Hills of the Taurus highlands are not ejecta from the Serenitatis basin and are most likely composed of distal ejecta from the Imbrium basin. Because this unit drapes the mountains near the Apollo 17 site, we contend that the Serenitatis basin provenance of Apollo 17 impact melts may no longer be assumed.

    We did NOT conclude that there was no lunar “cataclysm” (the lunar version of the LHB) — we offered two alternative scenarios, each with slightly different implications for lunar history. If the Apollo 17 rocks are from Imbrium, then we did not directly data the Serenitatis impact and with 25 basins and over 2000 large craters stratigraphically sandwiched between Serenitatis and Imbrium, it makes the “cataclysm” less necessary to explain lunar rock ages. It also implies that given the variations we see in the Apollo 17 impact melts, we do not fully understand this process for large-scale impact events.

    On the other hand, if the Apollo 17 impact melts ARE from Serenitatis (and there is no independent evidence to confirm this one way or the other), then not only WAS there a cataclysm, but it would have been a cataclysm in one of its most extreme forms — creating more than half of the observed lunar basins and highland craters all within a very narrow 30 million year time span.

    Please note well that we did NOT select one alternative over the other, nor should the reader infer that we have any preference for one over the other. We are simply stating that this geological issue — once thought to be a firm constraint to lunar history — is not as clear-cut as we had previously thought. In fact, there are two broad impact melt compositional groups at the Apollo 17 site and it is tempting to equate one (the so-called “poikilitic melt sheet”) with Serenitatis and the other (the “aphanites”) with Imbrium (the adjectives refer to their appearance under a rock microscope). But we do NOT so equate them because there are at present no objective grounds to do so.

    I am happy to send interested readers a PDF reprint of our full paper if they will e-mail me at [email protected]

    1. I would like to thank Paul Spudis for taking the time of making a very clarifying comment, as well as offering copies of the paper!

       And I would add that I believe this is the sort of public outreach that adds much value to modern science and its social effects.

       1. I agree completely Torbjörn Larsson:), This is exactly the sort of outreach that I think is not only beneficial for the individual researchers in question, but necessary to increase the public’s understanding of the scientific process.

    2. Paul Spudis’s blog is worth following too:

       http://blogs.airspacemag.com/moon/

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