ring_of_fire_crop_sharp_350pxThere are good reasons to think that Earth and Mars originally formed a single protoplanet—Terramars—outside the orbit of Jupiter.  Then, over 4 billion years ago, Terramars was pulled by Jupiter’s powerful gravitational field past the gas giant.  As Terramars neared Jupiter, tidal forces heated it to the melting point, and Jupiter tore Mars away from Earth, leaving the Pacific Basin.  Both planets, now turned into red-hot comets, sped off into the inner solar system.

In an early version of the old, generally discredited fission theory of the origin of the Earth-Moon system, the Pacific Basin was a scar left over from the separation of the Moon from a rapidly rotating Earth.  But according to the new theory, the geomagnetic field (modeled as if a bar magnet dipole were buried inside the Earth) is displaced 498 km off center in the direction of the Pacific Basin at 25º N, 153º E because Mars was separated from Earth there as Terramars passed Jupiter.  Not only the skew of the geomagnetic field but also the Pacific Basin itself, the seismically active Ring of Fire surrounding it, and the Hawaiian and South Pacific hotspots are physical leftovers from the separation of Mars from the Earth, as is the South Atlantic Magnetic Anomaly on the opposite side of the world whereby the Van Allen radiation belt comes close to Earth as a consequence of the skew in the geomagnetic field.

Given the long, tangled history of plate tectonics, continental drift, and other intervening phenomena, the present-day Pacific Basin has of course changed considerably since its origin in the Mirovia Ocean, later Panthalassic Ocean.  Still, seismic anisotropy1 reveals a unique pancake-like pattern at 160 km depth, approximately centered on the island of Hawaii, that could be left from an emergence of Mars, though this location would not necessarily have been the epicenter of the cataclysmic event since the South Pacific contains many features consistent with an emergence. In fact, a Mars exit would have left a gaping wound in Earth; and Mars could have been ripped off in such a way that the gash was oval instead of circular and extended far to the South.

The geology of the Pacific Basin contains many features consistent with an emergence of Mars, of which its roundness is an obvious one.  In a list of hotspot/melting anomaly locations, for instance, Pacific plate hotspots score consistently much higher in terms of flow rate than Atlantic and Indian Ocean counterparts, and they are only matched by several at the near edges of the adjacent Nazca and Australian plates.2  The 1-km high Hawaiian swell and the 500-m high South Pacific Superswell also mark the Pacific Basin as idiosyncratic.  At least in some areas, if seismographic slowness is interpreted as evidence of higher heat, the South Pacific Superswell appears to stand over a hot area of the mantle that extends down to the core.3  Volcanism in various South Pacific hotspots also varies from the normal Mid-Ocean Ridge basalts of the Atlantic in having higher vesicularity, more blocky/tabular flows and hornitos made of silica-enriched lava, and extreme end-members of radiogenic isotopes (indeed, these are extreme versus any isotopes in their class worldwide).4  In some areas of the South Pacific the lithosphere is significantly thinner than usual, and regular or intermittent pulses of magma appear to move upward from the mantle rapidly through a weakened lithosphere to erupt undersea or above sea surface, sometimes spreading over wide areas.5

In Cretaceous times, Pacific crust formation was unusually energetic.  This occurred at the same time as the curious Long Cretaceous Normal of the geomagnetic field during which there were no magnetic reversals between ~125,000,000 and ~85,000,000 years ago.  This must lead us to suspect an interaction between the mantle and the outer core dynamo that drives the geomagnetic field, with the Pacific Basin more affected than other regions.6

Two other pieces of evidence are consistent with the emergence of Mars from Terramars:  unlike with the Moon, which has 1:81 ratio of mass to that of the Earth, Mars has a mass of a 1:9.5 ratio to that of the Earth, which corresponds roughly to the size of the Pacific Basin; and the reversed polarity magnetic stripes of the southern hemisphere of Mars bear a remarkable resemblance to the magnetic stripes of the Earth’s seabed divergence zones as determined by reversals in the polarity of the geomagnetic field.  In effect, the southern hemisphere of Mars is the original surface (now much battered by impacts) of the Pacific Basin.

Thus we can see an explanation of the long controversy between plate tectonics and the plume hypothesis of hotspots:  the adherents of plumes and hotspots have mainly focused on the Pacific while the backers of plate tectonics have largely concentrated on the rest of the world, though they have also tried, somewhat less persuasively, to apply their model to the Pacific.

All of these phenomena are evidence of a tectonic regime that is very much what we might expect of the location of the emergence of Mars.


Kenneth J. Dillon is an historian who writes on science, medicine, and history.  See the biosketch at About Us.

1. C. Gaboret, A.M. Forte, J.-P. Montager.  The unique dynamics of the Pacific Hemisphere mantle and its signature on seismic anisotropy.  Earth and Planetary Science Letters 208 (2003), 219-33.  See especially Figure 4, p. 227.
2. G.R. Foulger and D.M. Jurdy, eds.  Plates, Plumes, and Planetary Processes.  Boulder CO:  Geological Society of America, 2007, pp. 65-78, replicated in G.R. Foulger.  Plates vs Plumes:  A Geological Controversy.  Oxford:  Wiley-Blackwell, 2010, pp. 15-6
3. Roger Hekinian, Peter Stoffers, and Jean-Louis Cheminée, eds.  Ocean Hotspots:  Intraplate Submarine Magmatism and Tectonism.  Berlin:  Springer, 2004, p. 253
4. Hekinian, pp. 197, 253
5. Hekinian, p. 370
6. Steven M. Stanley.  Earth System History.  2nd edition.  New York:  W.H. Freeman and Company, 2005, p. 431
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