Study questions scientific dating method


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The uncertainty of science: A new study has raised questions about the methods scientists have used to date the late heavy bombardment in the early solar system.

A study of zircons from a gigantic meteorite impact in South Africa, now online in the journal Geology, casts doubt on the methods used to date lunar impacts. The critical problem, says lead author Aaron Cavosie, a visiting professor of geoscience and member of the NASA Astrobiology Institute at the University of Wisconsin-Madison, is the fact that lunar zircons are “ex situ,” meaning removed from the rock in which they formed, which deprives geoscientists of corroborating evidence of impact. “While zircon is one of the best isotopic clocks for dating many geological processes,” Cavosie says, “our results show that it is very challenging to use ex situ zircon to date a large impact of known age.”

The problem is that the removal of the zircon from lunar rocks changes the data enough to make the dating unreliable. The method might work on Earth, but the dating done on Apollo samples can be questioned. This means that much of the supposed history of the solar system, centered on what planetary scientists call the late heavy bombardment, a period 4 billion years ago when the planets were being hit by innumerable impacts as they cleared the solar system of its dusty debris disk, might not have happened as dated from lunar samples. If so, our understanding of when that bombardment ended and life began to form on Earth might be considerably incorrect.

The solution? Get to the planets in person, where you can obtain many samples in situ and thus gather a much deeper understanding of the geology.

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7 comments

  • J Fincannon

    Not sure why you need people (“in person”) to go gather the samples. Robotic rovers gathering samples into a sample return capsule and launched from the Mars surface into orbit and then ferried back to some safe place in cislunar space for analysis would likely be cheaper than humans in the loop.

  • The key word in my statement was “many”. Rovers and sample return missions can only do a little. Moreover, the samples won’t be in situ, which is what the study found was very important. Put a lot of people on these planets to live and work and we will finally get a large enough in situ sample to learn the geology, in depth.

  • J Fincannon

    I do not have access to the entire report, but from the abstract and stories, I am not convinced it is necessary to have an actual person there to examine the samples in the context of their surroundings. If it felt to be of importance, a properly designed rover/robotic drill/imager/etc should be enough to provide the “in situ” context and analysis. Many such samples can then be examined by a large number of such rovers (if it is felt to be important enough to satisfy science with suitable funding for such a fleet). I doubt the science is adequate to justify human presence, especially on Mars when you may be jeopardizing potential Mars microorganisms (which is going to take a while to prove don’t exist so that it is safe to allow humans to be there).

  • Edward

    At this time, and as you noted, the priority for Martian exploration (landers, rovers, and orbiters) is finding existing or previous life on the planet and the water and other conditions that such life needs. Orbiters are finding places that could contain water, and thus life, and the rovers are being used to find ways to explore some or many of those places. Directing rovers and landers to examine for the age of the geological features is secondary. Even curiosity focuses its exploration on conditions that would support life (it is not designed to find organism, living or dead), or would have in the past, rather than on dating impacts; it is unlikely that rovers will be sent to Mars for this purpose.

    Now that NASA has declared that the US is going to put people on Mars in the next couple of decades, and considering that private groups are working toward colonization, the space community has accepted the inevitability of humans going to Mars, both for exploring and pioneering. It is clear that dating impacts is not the reason for going, but once we have a presence on the ground, dating impacts is one of the many exploratory tasks that can be undertaken.

    I do not believe that anyone was suggesting that we go to Mars just to find the age of some rocks. I believe that the suggestion is that, once we have arrived, we find their ages as one of the many activities that can and should be done on the planet.

    When we go back to the moon, finding the ages of impacts should also be one of the activities that engages our explorers.

  • J Fincannon

    You say we would unlikely use rovers to answer the aging question, but if we devoted our resources to rover science rather than the super-expensive human exploration, perhaps they could do not only secondary science but also tertiary tier stuff.

    Of course if we land people on Mars they will likely have time to look into the age question at their leisure. But it sounded to me from the article that they could just as easily obtain this information from the Moon. Landing on the Moon would likely be much cheaper to answer this question.

    I think it takes a great deal of hubris to have people walk on Mars before definitively determining that astronauts 1) will not impact existing Mars life and 2) will not be not “infected” by Mars life preventing them from returning. A lot of Star Trek mentality going on there… Beam down to any planet and not worry about destroying the ecosystem by a few bacteria we carry on our skin or gut. Or conversely, beam up a person carrying a plague of microorganisms. We did this with Apollo after astronauts “swam” (or at least breathed) in the lunar dirt and all we had was a fig leaf of a holding chamber to put them in on Earth for a few days that was “good enough”. We were lucky then.

  • Edward

    J Fincannon wrote: “but if we devoted our resources to rover science rather than the super-expensive human exploration, perhaps they could do not only secondary science but also tertiary tier stuff.”

    Agreed. Not only is manned exploration expensive, it is dangerous.

    But it is more than likely that we will send humans to Mars and back to the moon in the next few decades. We humans are less interested in sending robots and more interested in visiting in person, despite the expense or the danger. This is why people go places on vacation, visiting and hiking down the Grand Canyon rather than looking at photographs, and climbing into caves rather than sending in robots.

    Our robotic exploration seems to be more along the lines of expanding humanity into the solar system (and a search for extraterrestrial life) than pure research. We send many probes to Mars and the moon, where we intend to go in person, but not so many to Venus, where it would be tremendously difficult to visit. We are already spending a majority of our probes looking at future colonization spots, and the others seem to be comparing other astronomical bodies with Earth, Mars, and the moon.

    As we find what is common in the solar system, and as we discover extra-solar solar systems, we get a sense for how common life in the universe may be.

    A lack of life on the moon may be less a case of luck and more a case that no one could imagine (and still can’t) life that forms (evolves into life) in a vacuum. Isolating the astronauts seems to have been more of an after thought than a real fear.

    We also seem to have largely (though not completely) given up hope of finding life on Mars. Few of our recent probes have been looking for signs of existing life and seem to be looking for ancient conditions in which life may have been able to form — although whether or not it did form may be left for future probes or explorers to discover.

    Less than a century ago, popular science fiction depicted native life on Mars, and it was so believed to be true that a radio show frightened much of the East Coast with a story of Martian invasion. Today, a popular movie (and book) depicts a lifeless planet and a man declaring himself the first colonist.

  • J Fincannon

    Edward wrote: “But it is more than likely that we will send humans to Mars and back to the moon in the next few decades. We humans are less interested in sending robots and more interested in visiting in person, despite the expense or the danger. This is why people go places on vacation, visiting and hiking down the Grand Canyon rather than looking at photographs, and climbing into caves rather than sending in robots.”

    One really can’t make such a generalization. Notice that newer generations are becoming more focused into their virtual worlds, latest gadgets and computerized social networks. Older generations may have liked to actually go to a 3D real place, but current and future generations are likely to become more and more attuned to Second Life type virtual worlds or Oculus Rift type environments. They will be content to using haptic interfaces, 3D goggles and whatever the latest sensory simulation is to prevent actually being there (reducing risk and cost). This is more in line with robots and rovers in hazardous environments beaming 3D video to content consumers. Also, you have to face the fact that the future economy will not enable regular people to visit Mars or even the Moon. With robots taking over more and more people’s jobs, with a larger population, I do not see regular people having the resources to go on a space trip.

    Edward wrote: “Our robotic exploration seems to be more along the lines of expanding humanity into the solar system (and a search for extraterrestrial life) than pure research. We send many probes to Mars and the moon, where we intend to go in person, but not so many to Venus, where it would be tremendously difficult to visit. We are already spending a majority of our probes looking at future colonization spots, and the others seem to be comparing other astronomical bodies with Earth, Mars, and the moon.”

    I do not agree with this at all. We send a spacecraft to Pluto for science. To asteroids, comets, Saturn, Jupiter, Mars, Venus and all the moons and our Moon for science. Now, you can argue with the merit of science data gathering and whether it is really of value to the average person, but there are no signs that this is done for “colonization”. Venus doesn’t get so many probes landing because it is so difficult, not because it is hard to get humans to live there. By the way, “colonization” is a really loaded word which you will find is unacceptable to most of the world. “Settlement” might be better.

    Edward wrote: “A lack of life on the moon may be less a case of luck and more a case that no one could imagine (and still can’t) life that forms (evolves into life) in a vacuum. Isolating the astronauts seems to have been more of an after thought than a real fear.”

    Carl Sagan proposed that life could still exist on the Moon at deep enough level below the surface. He was very concerned that astronauts would contaminate it by their presence. Early lunar robotic landers were sterilized to the point of failure, which made the managers infuriated in their attempts at successful landing. There were people that had a “real fear”. Read http://history.nasa.gov/SP-4234.pdf Carl Sagan warned that “there was a remote possibility that lunar explorers might bring deadly organisms back with them that could destroy life on Earth.” The Space Science Board issued a warning in the June 1962 report of its Iowa City Summer Conference, advising that the introduction of alien organisms into the biosphere of our planet could cause “a disaster of enormous significance to mankind” and recommended that “NASA do everything possible to minimize the risk of back contamination.” The Apollo 11 astronauts were in quarantine for 1 month. There were congressional hearings about how to protect the Earth from this problem prior to Apollo 11. No afterthought.

    Edward wrote: “We also seem to have largely (though not completely) given up hope of finding life on Mars. Few of our recent probes have been looking for signs of existing life and seem to be looking for ancient conditions in which life may have been able to form — although whether or not it did form may be left for future probes or explorers to discover.”

    Who is this “we”? “We” haven’t really seriously looked.

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