Exposing PseudoAstronomy

October 23, 2008

Venus and the Battle of Uniformitarianism (A Creationist Argument)


This entry is in specific response to the “Venus vs. Uniformitarianism” article from the Institute for Creation Research, written by David Coppedge.

This is meant to be a short post on the heels of my crater discussion from yesterday, and it actually fits in fairly nicely even though it’s about something completely different:  The planet Venus.

Venus is an interesting planet and has held peoples’ imaginations ever since it was realized that it was shrouded in clouds, hiding its surface from view.  At almost the same size as Earth, it was long thought of as Earth’s twin and it may hide a paradise beneath the atmosphere.  That view vanished in the 1960s when spacecraft showed it to be a planet with a surface temperature far above the boiling point of water, the clouds full of sulfuric acid, and the atmosphere so heavy that the surface pressure is the equivalent of being under 1 km of ocean on Earth.

But another highly unexpected observation was that Venus’ entire surface seemed to be the same age based off of the crater population (see, there is a link to my post yesterday!).  There are just under 1000 craters on Venus, and statistically they are distributed randomly over the planet, no region being older nor younger than another (to the accuracy of crater age dating).  And then, based off of the crater density, the surface age of Venus was estimated to be 500 million to 1 billion years old (the agreed-upon number today is about 700 million).

(Note that a pretty good, definitive paper on this is found in the Journal of Geophysical Research, vol. 97, No. E10, from 1992 in an article by Roger Phillips et al. entitled “Impact Craters and Venus Resurfacing History.”)

The question is:  What would make the entire surface a single age, between 11-22% the estimated age of the solar system?  That brings us to the Institute for Creation Research article I cite at the beginning of this post.  David Coppedge uses Venus to say that it “poses a serious challenge to uniformitarian views,” (views that say geologic history has resulted from the action of continuous and uniform processes throughout time; in other words, the opposite of catastrophism).

This is actually true.  It’s very difficult to think of a uniformitarian process that would produce what we see on Venus today.  That’s actually why no one really does (hence, it is a straw man argument, an argument against something that the other side doesn’t actually say).  The prevailing view today is that Venus’ current surface is the result of a catastrophic release of magma from within the planet that broke through the crust and covered the planet in a geologically short period of time – hundreds or thousands of years.

The proposed mechanism is that without plate tectonics to release heat and energy, the build-up in the planet’s mantle eventually overpowered the strength of the crust, resulting in the catastrophic release.  It is possible that this is cyclical, occurring once every few hundred million or few billion years – we just don’t know because we (a) haven’t seen it and (b) we can only see the evidence from the last time.

Why this becomes important to creationists, and why it’s on the ICR website, is two-fold.  First, creationism relies upon catastrophic events to explain geologic features like the Grand Canyon (general appeal is to Noah’s Flood).

Second, which is the point of the last two paragraphs of the ICR article, is, “One idea never considered is that the missing 90% never occurred.”  So he is arguing for a young solar system based on the data showing that Venus’ surface is ~700 million years old.  There are many, many things wrong with this argument, but for the sake of my promised brevity, I will only address two.

The first should be obvious:  For creationist arguments, the goal is to get the age of the solar system down to 6000 years or so.  However, it shouldn’t take a math major to figure out that 700,000,000 is much greater than 6000 … by a factor of over 100,000.  The point of the article is more likely to try to make the reader second-guess the “millions of years” arguments rather than have the reader actually think of the timescales that are being suggested.

Second, and this is more subtle, he is still relying upon an argument from crater age dating.  This has been calibrated from the Moon.  So let’s say that the lunar timescale were off by, oh, a factor of 1,000,000 (what’s needed to get it to 6000 years).  Remember from my post yesterday that crater age dating is relative, and so that would mean that Venus’ age (since the article is suggesting that its surface age is the same age as the planet) is also younger by a factor of a million.

That would place Venus’ age at between 500 and 1000 years old.  Not even creationists think that Venus is that young – they can’t, because there are historic records dating back over 4000 years showing observations of Venus.  As you can see, if you actually think about these arguments logically, and carry them through to their conclusion, they become unrealistic unless there is some sort of “other” special happenstance.  You can’t pick and choose how far you want to take the evidence, as they do in this article.

Finally, I want to end with two comments on the last paragraph of the article.  First, “If it were not that Darwinian evolution requires vast ages …, many of the features observed by the space program would be considered young.”  This is not true.  Geologists had already figured out Earth was at least on the order of millions of years old before Darwin ever presented his theories on evolution.  Geology in terms of figuring out how old things are has absolutely nothing to do with biological evolution.  It has much more to do with basic physics, such as heat transfer, collision rates, gravitational perturbations, etc.  Nothing in space is dated based on an idea that evolution says something has to be old … this is an absolutely ridiculous claim showing naïveté, especially coming from someone who “works in the Cassini program at the Jet Propulsion Laboratory.”

Now that I have that out of my system … second, a more philosophical point:  “Should scientists be allowed to infer histories that are indistinguishable from myth?”  Speaking as a scientist, the idea that I can or can not formulate a history from on my observations based on the whim of whether someone else thinks I should or shouldn’t be allowed is very … irritating.  Who is he to say whether someone can or cannot think something?

Science works by lots of people coming up with lots of different possible explanations based on the observations.  They can then test those explanations by making predictions for further observations, and those observations should be able to rule out some of the explanations and still allow others.  Then the process repeats until (hopefully) one is left that explains all the observations.  If none do, then a new hypothesis must be built that can explain all the observations, and then be further tested.

The “catastrophism” idea for Venus is not presently testable due to financial and technological constraints.  However, there are ways that it can be.  One would be sending ground-penetrating radar to Venus to peer within its crust and determine heat flows.  Another would be to find fissures across the planet that could be outlets for the resurfacing material.  A third would be to actually date material on the surface and to dig down within the crust and date that material, as well.  The argument from the article – that the first 90% of Venus’ history never actually existed – is not testable at all, nor does it make sense in the context of the rest of the solar system (as discussed in my demonstration that Venus would need to be 500-1000 years old based on this article).

October 21, 2008

Dating Planetary Surfaces with Craters – Why There Is No “Crisis in Crater Count Dating”


This entry is in specific response to the “Crisis in Crater Count Dating” article from the Institute for Creation Research, written by David Coppedge.

How can astronomers say that Mars had recent volcanism?  Or that the surface of the moon Io is younger than 50 years?  Or that the youngest stretches of terrain on our moon’s surface dates back to about 3 billion years ago?  The answer is one of the basic tools of comparative planetology:  Impact craters.

Impact craters are ubiquitous throughout the solar system – every single solid body has craters on its surface except for the moon Io (because its surface is so young due to the incredible amounts of vulcanism).  Impact craters form when an impactor – like an asteroid or comet – hits the target surface of a planet or moon.  The impact occurs at high speed, and the final crater depth, diameter, and shape are effectively determined by the surface gravity, the mass of the impactor, and the velocity of the impactor.  Almost all impact craters are circles; only impacts at very low angles (less than 10°) will form elliptical craters.

Note:  There are craters of other origins, such as pit craters or caldera craters at the top of volcanoes.  Only impact craters are used to date surfaces, and for brevity I will only be referring to them from this point on as “craters” instead of “impact craters.”

The basic idea behind using craters as an indicator of a surface’s age is that the longer the surface is around, the more craters will form.  If an impactor were to hit a target at a rate of 1 per year, then a surface that’s 1,000,000 years old should have 1,000,000 craters.  But if that surface were to have something happen to it, like it got covered by lava, then that would erase the craters and the crater age would be set back to 0.

That’s effectively what people do in order to date the surfaces of planets or moons that are not Earth:  We count the number of craters of different sizes for a part of the surface and then compare that with the rate of impacts of that size.  This is called “crater age dating,” and it is a form of “relative age dating.”  The reason that it’s relative is that it cannot give an absolute age in years, it can only say if a surface is statistically older or younger than another surface.

To actually calibrate the number of impactors of a given size to an absolute age requires us to date the rocks within that surface.  This was one of the science results from the Apollo lunar missions – samples brought back from the moon were dated in the lab and hence an absolute age could be assigned to surfaces with a certain density of craters (number of craters per area).  This can then be extrapolated to other locations in the solar system.

Craters form in all sizes – from microcraters on airless bodies like the moon to giant basins literally 1000s of kilometers across.  In general, researchers use craters that are on the 10s of meters scale to about 1 kilometer, or a few kilometers to a few 10s of kilometers for age dating (at present, there is a general mismatch gap in what is used; this is generally because the meter-scale craters are used to date smaller, isolated surface areas whereas kilometer-scale craters are used to date much larger geologic units that cover a significant percentage of the planet or moon).

One more piece of background information is that when craters form, they send up clouds of debris, from dust-sized particles to objects up to a few percent the size of the original impactor.  These larger chunks of material are ejected outwards from the forming crater, and they may end up forming their own craters.  These are called secondary craters since they were formed as a result of the original, or primary crater.

Secondary craters are different from primary craters in the way they look because of their formation history — mainly they are much smaller and they are also shallower.  This is both because the ejected material that formed them was much smaller than the original impactor and because the velocity of the debris is much less than the original impactor, so there is significantly less energy to form the secondary crater.  Observations and computer models have shown that the largest secondary craters can only be up to ~5% the diameter of the primary crater (observations made on Earth, Moon, Mars, Mercury, and Europa), although the vast majority are much smaller than 1% of the primary.  In addition, secondary craters that form closest to the primary (within about 10 crater radii) are usually very easy to identify as secondary due to the way they look and the surrounding surface.

The point of this background it that crater age dating has been used for over 50 years, and it rests on very solid theoretical, experimental, and observational grounds.  However, you wouldn’t think that given the ICR article, “Crisis in Crater Count Dating:”  “New thinking about ‘secondary craters’ has thrown this whole foundation of comparative planetary dating into disarray.”

The article continues with misleading statements:  “One writer in Nature estimated that a single large impact on Mars could generate 10,000,000 secondaries, and that 95% of the small craters on Europa could be from fallback debris.”  You are clearly expected to infer from this that almost all craters (95%) on surfaces are secondaries by simply connecting those two phrases together.  That may actually be true.  But there is no size range stated.

Those same authors, Alfred McEwen and Edward Bierhaus, who are not mentioned in that quote wrote a paper in 2006, “The Importance of Secondary Cratering to Age Constraints on Planetary Surfaces,” in the Annual Review of Earth and Planetary Science.  I highly recommend reading it if you are interested in this subject, and it is written at a non-technical level.

In their paper, they show that yes, secondary craters do dominate planetary surfaces, but for Mars (the object of interest at the moment), the critical diameter at which secondary craters dominate is about 1 km.  Craters smaller than 1 km are likely >50% secondaries, but craters larger are >50% primaries.  And because a significant amount of age dating is done with craters larger than 1 km, there is no way that “this whole foundation of … planetary dating [is in] disarray.”

The ICR article goes on from there, and either shows the author’s ignorance of the issues or that they are simply lying:  “Without a way to reliably identify secondary craters …”  As I stated above, the majority of secondary craters that are close to the primary can be identified because of their distinct shapes and characteristics – they are shallower, they are often elongated with the long axis pointing towards the primary, they appear in clusters, and there are generally trails of them that lead back to the primary.  One could also ask the question, “If there were no ‘way to reliably identify secondary craters,’ then how could we know that there even are secondary craters?”  Granted, it does become more difficult the farther from the primary crater and the smaller the secondary, but this becomes a non-issue when using large craters.

But, you can still use small craters to date planetary surfaces.  One of the arguments used is that reference crater densities that indicate a certain age for a surface were created  without taking secondary craters into account – in other words, they have both primary and secondary craters in them.  So when using them to date a surface, it doesn’t matter if there are plenty of secondary craters there because they are in your reference, too.

Besides this, this topic is still in active debate at planetary astronomy conferences today (William Hartmann and Gerhard Neukum are two of the strongest proponents that secondary craters aren’t even an issue for sub-kilometer age dating).  In fact, I was just at a conference – the Division of Planetary Science for the American Astronomical Society held at Cornell University in Ithaca, NY (October 2008) – where Dr. Hartmann presented results which indicated that secondary cratering is not a problem at sub-kilometer diameters for age dating.

In the last crater-related point I want to address from the article, it implies that astronomers applied crater age dating from the moon to other objects “believing they knew how old the earth-moon system was.”  This is true, but it’s not true the way they imply it.  From this statement (the next-to-last paragraph of the article), you are clearly meant to think that we used crater ages from the moon to go to other bodies, but if we don’t even know how many craters equals 1 year or 100 years or 1000 years on the moon, how could we possibly know what it means on other objects?

The answer should be apparent given the background I discussed above:  Craters give relative ages, while radioactive decay dating methods give absolute ages.  We applied the relative ages from the crater densities on the moon to other bodies, so it doesn’t really matter if we don’t know how old that surface is on the moon for that exercise.  But then we can calibrate the relative scale with the absolute scale from the moon because we have independently dated its surface with a completely different method.  Therefore, the ICR article is yet again trying to mislead the reader.

The final point that I would like to address is the article’s last sentence:  “There is an important lesson here, though, for all science lovers:  question assumptions.”  (emphasis mine)

I whole-heartedly agree.  You should question assumptions.  You should try to understand why someone says what they do.  You should do your own research, your own experiments, and make your own observations.  You shouldn’t take my word for it, you shouldn’t take ICR’s word for it, you should go out and look for yourself.

Finally, you should always question someone’s assumptions, especially if they are based in an ideology:  If they start from the premise that the Bible is Truth, the literal word of an omnipotent and infallible deity, and then try to make all observations fit within that view, you should be questioning that assumption.

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