The ultimate expanding earth hypothesis

In the introduction to his paper on transPacific relationships, McCarthy (2003) agrees with an extreme view of the expanding earth theory that calls for a small, pre-Jurassic globe that was completely terrestrial. His reasoning is straight forward: the floor of all the world’s oceans was formed less than 200 Ma, therefore oceans did not exist prior to that time. Of course, this is a reasonable thesis only if one is prepared to ignore a number of well-established facts: (1) the Precambrian to Paleozoic fossil record of marine life providing evidence of extensive oceans; (2) the failure of the expanding earth theory to pass a rigorous paleomagnetic test (McElhinny et al., 1978); (3) the absence of cracks across the planet caused by expansion (Hallam, 1994); (4) The absence of a drastic fall in sea level since the Triassic that would have been caused by expansion; (5) the abundant evidence of large-scale subduction that absorbed the older sea floor; (6) the lack of evidence for the generation of the internal energy necessary for expansion (Bursa & Hovorkova, 1994); and (7) no evidence of the rapid reduction in the earth’s rotation that would be caused by expansion (Bursa, 1993). A less extreme view of earth expansion was published by Owen (1976) and this was followed-up by his Atlas of Continental Displacement (Owen, 1983). Owen felt that he had geological evidence that the continents could fit together to form Pangaea only if the earth’s diameter was 80% of its modern mean value. Otherwise, a reassembly of the continents from their present positions back to their pangaean beginning would leave a series of large V-shaped gaps. Owen’s maps, illustrating a 20% expansion over the past 200 Ma, were of interest to a number of biogeographers. However, Weijermars (1986) showed that if a three-dimension globe is used, instead of map projections, the gaps will disappear. The concise review published by Cox (1990) should have laid the expanding earth theory to rest, but alas it has arisen once more. The expansionist paper by McCarthy (2003) maintains that the Pacific Ocean was formed by the separation of the west coast of the New World from the east coast of Asia and that this event took place in less than 200 Ma. In support of this idea, he utilizes two kinds of evidence, geological and biological. The former consists of arbitrarily shifting continental blocks and oceanic trenches about so that, in the Triassic, the shorelines of the two sides would fit together. It may suffice to say that geophysical evidence of such an arrangement is lacking. The major part of his argument consists of extensive literature references to transPacific animals and plants that are supposedly unable to achieve long-distance dispersal. The authors of the referenced articles are, in large part, people who share the expansionist philosophy. Even so, a general rebuttal to such information may be of interest to biogeographers. The great bulk of the biological evidence (about five pages) is devoted to relationships across the Southern Ocean and, in particular, emphasizes the supposed juxtaposition of New Zealand and the southern part of Chile. Plate tectonic reconstructions (Lawver et al., 1992) for the late Cretaceous show that the tip of the Antarctic Peninsula was located close to Tierra del Fuego and that Tasmania, and the South Tasman Ridge, formed a connecting link between Australia and Antarctica. These positions remained relatively static until the late Eocene, about 40 Ma, after which Australia moved rapidly northward. The drop in sea-level at the end of the Cretaceous (Hallam, 1994) allowed considerable exposure of the continental shelves that lessened the distance between shore lines, and provided increased opportunity for migration of the terrestrial biota. The window of migratory opportunity, that was available from about 60–40 Ma, permitted the formation of what is often called an amphinotic track . The strongest ties are between South America and Australia followed by New Zealand. More distant relations are shown by southern Africa, Madagascar, and New Caledonia (Briggs, 1995). Australian–South American relationships are demonstrated by a large fraction of the flora and fauna. The list includes vertebrates such as the marsupial mammals, xiphodont crocodiles, the frog family Leptodactylidae, the turtle family Chelidae, ratite birds, and mound birds. The invertebrates include freshwater mussels, crayfish, and aquatic insects such as the mayflies, stoneflies, caddiceflies, and others. Also included are a host of terrestrial invertebrates such as land snails, oligochaete worms, and most major groups of insects and spiders. Like Australia, New Zealand probably received its earliest vertebrates (dinosaurs, a leiopelmatid frog and its tautara species) in the Triassic or Jurassic. But, during the early Tertiary, it too received an infusion of biota from South America via Antarctica and Australia. Unlike Australia, New Zealand received no vertebrate animals at that time except birds and possibly some lizards. The ratite birds, moas and kiwis, probably arrived in the early Tertiary. Their migration was facilitated because their ancestors were probably flying birds related to the South and Central American tinamous (Briggs, 2003). A review of the origins of the New Zealand flora (Pole, 1994) indicates a close relationship to Australia, and that the present vegetation of the former is entirely, or almost entirely, the result of long distance dispersal during the Tertiary. It should be noted that not all of the amphinotic migratory traffic moved from west to east. From southeast Asia to the general Australian–New Zealand region, there is a remarkable concentration of primitive conifer and angiosperm families. A few of them are found in South America and it is likely that they arrived from the east. Journal of Biogeography (J. Biogeogr.) (2004) 31, 855–857