Another expanding Earth paper

Authors


A response to D.McCarthy (2005) Biogeographical and geological evidence for a smaller, completely-enclosed Pacific basin in the Late Cretaceous. Journal of Biogeography, 32, 2161–2177.

Despite the fact that the expanding Earth hypothesis has been discredited to the point that most palaeontologists, geophysicists, and biogeographers do not give it serious consideration, it keeps reemerging. The new paper by McCarthy (2005) reiterates the same extreme version that was proposed in his 2003 publication. It is his belief that in the Late Triassic, c. 200 Ma, the Earth was a small, completely terrestrial globe. Since that time, the Earth has supposedly ballooned to about four times its previous size. Although his 2003 paper was severely criticized (Briggs, 2004), McCarthy persisted in gathering more data that he considered to be evidence for his theory. He has yet to show, however, that the criticisms of his 2003 work were invalid or unimportant.

Briefly, the criticisms levelled against (McCarthy's 2003) paper were his failure to explain some well-established facts: (1) the Precambrian to Palaeozoic fossil record of marine life indicating extensive oceans, (2) the absence of cracks across the planet caused by expansion, (3) the absence of a drastic fall in sea level that would have been caused by the expansion, (4) the abundant evidence of large-scale subduction that absorbed the older sea floor, (5) the lack of evidence for the generation of the internal energy necessary for expansion, and (6) no evidence of the rapid reduction in the Earth's rotation that would have been caused by such expansion. In addition, his theory fails to pass a rigorous palaeomagnetic test.

In regard to the first criticism, McCarthy (2005) observed that no pre-Jurassic marine fossils have been found in the present oceans. Of course this is true, because all of the older sea floor has been subducted. There is, however, plentiful evidence from fossils that existed in deep parts of former oceans lifted above sea level by tectonic action. For example, Tolmacheva et al. (2001) reported abyssal deposits of radiolarians and conodonts that provided evidence for 15 Myr of continuous sedimentation in the early Palaeozoic oceans. McCarthy maintained that the early marine environments were really epicontinental seas, but epicontinental seas or lakes do not have the biological or chemical characteristics of abyssal environments.

In considering the lack of data indicating a drop in sea level as the globe expanded, McCarthy (2005) stated that the most obvious mechanism for the origin and increase of seawater was expulsion from hydrothermic vents. Moreover, he referred to estimates that the entire volume of the Earth's oceans passes through the vent systems every ten million years. However, the vents are recognized as part of an in-and-out system; that is, seawater penetrates fractures in the ocean floor, reacts with the hot rock below, and returns via the vent system. No one has proved that the vents are the source of new seawater. McCarthy also refers to the presence of hypothetical, massive reserves of water in the Earth's mantle. Although most minerals of the Earth's upper mantle contain small amounts of hydroxyl (OH) (Bell & Rossman, 1992), there are no indications of massive reserves.

McCarthy (2005) did not attempt to reply to the other criticisms of his 2003 paper, but instead concentrated on discussing data that, in his view, provided support for an expanding Earth. Despite the enormous amount of geological and geophysical research that demonstrates the reality and mechanics of plate tectonics, McCarthy still does not believe it. He devoted considerable space to numerous palaeomagnetic measurements culled from a large literature in an attempt to prove that the Late Cretaceous Pacific Plate was completely enclosed by surrounding continents, and that it pushed them apart as it expanded. This effort can only be described as futile, for the tectonic history of the Plate is well known and there are good computer animations available. An authoritative series was drawn and animated by Tanya Atwater and may be seen on the website of the University of California at Santa Barbara (http://www.geol.ucsb.edu).

McCarthy (2005) also devoted considerable space to criticizing the tectonic relationship between Gondwana and south-east Asia that had been published by Metcalfe (1998). Here, his objections were based mainly on biogeography rather than palaeomagnetism. I had recently published an article on the biogeographic and tectonic history of India (Briggs, 2003), and McCarthy used some of that material in an attempt to bolster his theory. Based on fossil evidence of its Late Cretaceous relationships, I illustrated India as lying closer to Africa and Asia than did most other reconstructions. McCarthy claimed that in so doing I had narrowed the Tethys, and that a narrow Tethys fitted his scheme. However, my changing of India's position did nothing to affect the size of the Tethys for, in the Late Cretaceous, it was a huge ocean stretching far to the east and west.

To help substantiate the fact that India underwent a considerable crustal shortening as it contacted Asia, I used two palaeomagnetic references. McCarthy objected to one of them (Zaman & Torii, 1999) because the locality was in northern Pakistan instead of India. However, tomographic imaging of the mantle (Van der Voo et al., 1999) indicated that the northern part of the Indian lithosphere (Greater India) had indeed penetrated that far north, thus accounting for its subaerial disappearance. The point is that Greater India before its subduction could have been close to or in contact with Asia. At the same time, the southern tip of India could have been close to or in contact with Madagascar. Such relationships can explain much of the terrestrial biogeography in that part of the world (Briggs, 2003).

To support his view that Australia had always been connected to south-east Asia, McCarthy (2005) compiled an extensive list of supposed biotic relationships to prove his point. His list included a variety of lizards, freshwater fishes, primitive mammals, and dinosaurs. He emphasized dinosaur biogeography, so it may be worthwhile to consider that evidence. He referred to literature on a wide variety of Australian dinosaurs and provided quotes from the website of the Museum Victoria. The quotes stated that Australian dinosaurs were apparently more closely related to those of Asia and North America than to the ones in South America. This was considered by the Museum website to be incongruous because Australia, Antarctica, and South America were at one time connected. Australia's external connections took place, however, during two distinct time periods. Dinosaurs and primitive mammals were able to invade during a Gondwana connection in the Triassic and Jurassic. After the Jurassic, Australia was apparently isolated because its Cretaceous tetrapod fauna was considered to be relict in comparison to that of the rest of the world (Molnar, 1992). The second connection between Australia, Antarctica, and South America took place in the Early Tertiary (c. 60–40 Ma), when much of the extant Australian biota, including marsupial mammals and ratite birds, arrived (Briggs, 1995). By that time, dinosaurs had been extinct for at least five million years.

The amalgamation of the Triassic continents to form Pangaea allowed all of the tetrapod faunas, including the early dinosaurs, to achieve a worldwide similarity (Benton, 1990). It was not until the mid-Jurassic that tectonic events began to play a major role in dinosaur evolution (Upchurch et al., 2002). Previous to that time, dinosaurs had populated virtually all parts of Pangaea with little or no indications of regional endemism. The supposed direct relationship between the dinosaurs of Australia and those of East Asia is based on fragmentary evidence from a poor fossil record. In fact, at the family level, the Australian Early Cretaceous tetrapod fauna as a whole was most closely related to that of South America (Molnar, 1992).

McCarthy's Australian–East Asian evidence based on lizards, snakes, and a freshwater fish is also suspect. Several lizard clades are widespread in the Western Indian Ocean region, and many of them are notorious transoceanic travellers (Rocha et al., 2006). Some snakes of the family Elapidae are also adept at over-water dispersal. The closely related Hydrophiidae are mostly marine. The freshwater fish example was the arowana, and McCarthy relied on a paper by Kumazawa & Nichida (2000). Those authors did not indicate a direct relationship between Australia and East Asia. Instead, they postulated a Gondwanan origin and migration into Asia via India or smaller continental blocks. Large-scale direct invasions of Australia from East Asia did not begin until the Miocene approach of the Australian Plate and the formation of the Indo-Australian Archipelago.

McCarthy (2005) apparently felt that his cause would be strengthened if he could demonstrate that, in the Late Cretaceous, the Pacific Ocean had been completely enclosed by land. He illustrated this arrangement by his map (his Fig. 1c), and for proof he depended primarily on dinosaur data. However, without the ability to maintain Australia in its present position, there was no way to visualize a land bridge across the South Pacific. Of course there were dinosaurs in Asia and in the Americas, and, in the Late Cretaceous, they came across the Bering Land Bridge. There are also indications of some traffic between North and South America. There was, therefore, a time when dinosaurs did extend around the northern half of the Pacific, but there is no logical way to relate this pattern to Earth expansion.

In conclusion, it must be said that this new effort to promote the expanding Earth hypothesis has no more validity than the 2003 paper. It is regrettable that so much effort and attention should be devoted to a theory that is scientifically untenable.

Biosketch

John C. Briggs was named Professor Emeritus on his retirement from the University of South Florida in 1990. His research deals primarily with the origin and distribution of contemporary groups of organisms. His biogeographical books include Marine Zoogeography (McGraw-Hill, 1974), Biogeography and Plate Tectonics (Elsevier, 1987), and Global Biogeography (Elsevier, 1995). In 2005, Professor Briggs received the Alfred Russel Wallace Award from the International Biogeography Society for his lifetime contributions to biogeography.

Editor: Robert McDowall

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