You and Mike are certainly correct that my first post was especially short on empirical evidence. My second pointed out that there are things that can be said in response to the objections which Mike had stated. Naturally others will make their own judgment about the adequacy of these responses, and the status of the discussion. I certainly don't claim to have Mike's level of general expertise in geology, only reasonable discernment abilities.

You seem convinced that a host of observations contradict expansion, while the converse assumption remains unimpaired. About the first part of this statement, I've already had my say, but here I'd just like to reiterate, having listened again to the show, and perused some of the referred show links, how many of the observations that actually are mentioned are quite consistent with Earth expansion. For example, at the point where the show mentioned GPS, it referred to the rate that Atlantic is becoming wider. It also mentioned Australia's northward movement (which is a way of alluding to the widening of the southern ocean – the increase in distance of the other continents from Antarctica). Evidently, the _need_ for evidence regarding the rate that the perimeters of the Pacific and Arctic oceans are _converging_ did not even occur to the presenters – which in principle would be a straightforward way to disprove Earth expansion.

This leads us to the converse question of whether the static-radius hypothesis remains consistent with observations to date. Maxlow points out in the online lecture I cited earlier, that the rate at which new crust is being extruded in the Pacific is about twice the rate of the combined Atlantic and Indian Oceans. Similarly, the apparent lack of evidence for convergence in the Arctic has been dubbed by some the 'Arctic Paradox'. Are these not at least difficulties for the Plate Tectonic theory?

Last night, I had the chance to look at a couple of animations of Plate tectonic models of the history of plate motions during the last 20 percent of Earth history (Berkeley, Enchanted Learning). I dare others to take a look at these and also the model animations produced by Maxlow as attachments to his PhD thesis (which cover almost 100 percent of Earth history) or those by comic book artist Neal Adams (which cover evidence not only from the Earth, but also from the Moon, Mars, Europa and Ganymede), and not harbor seeds of doubt about the Plate Tectonic paradigm. (Links can be had through their respective eponymous websites.) Recall that Maxlow's models are based in straightforward ways on the UNESCO Geological Map of the World; the pre-Jurassic ones are less straightforward, to be sure, but still follow clearly stated rules (in part involving gradually restoring continental sediments to where they came from). Note that in this model, both the Atlantic and Pacific oceans were closed less than 180 million years ago. Specificially, Australia and North America were in contact at that time. I was interested to to watch the Berkeley animation showing the Atlantic closed at about that time, and Australia converging with North America 800 million years ago. So Plate Tectonics indeed holds that there was convergence of continents around the Pacific, but asserts that the convergences occurred at different times. Quite apart from the superior quality of the growing earth animations themselves, I think they possess a striking simplicity and elegance which the Plate Tectonic ones lack.

I wish to thank the Astronomy cast team for their indulgence so far. I will copy this post to Mike's e-mail, to provide for the possibility of continuing this discussion offline.

And, again, without disagreeing with your points, I would note that science is not democracy: we may have dozens of of observations that bolster a particular theory, but that theory may be invalidated by a single legitimate counter-observation. I am very skeptical and science-based in my thinking, but anyone who knows the history of geology knows that for years the idea of "Continental Drift" was considered to be a crackpot theory by the geoscience mainstream, which had lots of observations that supposedly buttressed the geosynclinal theory for mountain building without recourse to moving and colliding continents. My point here is that science is a human endeavor, and personal bias, dogmatism, interpersonal relationships and faulty logic do occasionally inform its practice.

By the way, if anyone wants to continue this discussion offline and cease filling up the Astronomy Casts' pages with what is actually a tangential discussion (tangential to their main topic, that is), I can be reached at darwin5056@yahoo.com. If we want to continue it here, that's fine with me assuming Fraser, Dr. Gay, and their web folks don't mind.

The asserted "knowledge" is conditional; it merely refers to a necessary consequence of the _assumption_ that the earth isn't expanding. It has exactly the same status as the knowledge, given the strong evidence for crustal spreading at mid ocean "spreading centers" around the world, that if crustal subduction is not occurring somewhere, the earth _must_ be expanding.

This is making the assumption that science is inductive, which is an error, and moreover an error adopted by different groups of believers to make equivocation. (Whether creationists, philosophers or crackpot theorists.)

Science can, and does, test theories against predictions to exclude the erroneous ones. Thus in one swell action observations, assumptions and the rest that the theory includes is tested as "good enough".

Here, as Mike points out, expansion contradicts a whole lot of observations while the converse assumption does not. Any amount of details can't, not even "extra-ordinary evidence", move that fact any more. Done deal.

[I would also like to add, if not Mike covered it already, that the show gave an from geology independent method, by GPS, to accurately test the hypothesis that the Earth is expanding.]