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using satellite laser ranging and radio astronomy are now accurate to less than one centimetre. These measurements show that the North American plate is moving west at about 16 mm/year, while the North Pacific plate is moving west-northwest at between 45 and 70 mm/year. The sum of these motion vectors means that the two plates are actually moving apart, not subducting, and the East Pacific mid-ocean-rift zone is extending north along the San Andreas fault (see figure 1). On an expanding Earth, subduction to the extent that plate tec- tonics requires does not exist. The values of 22 mm/year, calcu- lated for increase in Earth radius per year, and 140 mm/year for circumference, are adequate to account for all sea-floor growth since the Early Jurassic period, without the need to consider removal of excess sea-floor crust. using satellite laser ranging and radio astronomy are now accurate determine the ancient radius of the Earth. From measurements of to less than one centimetre. These measurements show that the the ancient radius, it was concluded that the radius of the Earth has North American plate is moving west at about 16 mm/year, while remained constant with time. This conclusion continues to be a the North Pacific plate is moving west-northwest at between 45 key issue in rejecting Earth expansion. and 70 mm/year. The sum of these motion vectors means that the In establishing palaeomagnetics, geophysicists during the early two plates are actually moving apart, not subducting, and the East 1960s made a fundamental assumption that the surface area of all Pacific mid-ocean-rift zone is extending north along the San continents has remained constant with time, with continental crust Andreas fault (see figure 1). being added or removed from around the margins during conti- On an expanding Earth, subduction to the extent that plate tec- nental collision or break-up. In determining the ancient Earth tonics requires does not exist. The values of 22 mm/year, calcu- radius, palaeomagnetic measurements were taken from sites sepa- lated for increase in Earth radius per year, and 140 mm/year for rated by up to 5,000 kilometres, and it was assumed that the conti- circumference, are adequate to account for all sea-floor growth nental crust between the sites had remained constant and stable. since the Early Jurassic period, without the need to consider Modern plate tectonics now says that continents are made up of removal of excess sea-floor crust. fragments randomly accreted during continental assemblage, break-up and dispersal cycles—which makes the conclusions = What about orogenesis? based on ancient radius measurements invalid. The term orogeny, or orogenesis, originally meant "the origin Modelling studies have demonstrated that ancient magnetic of mountains". Since the advent of plate tectonics, orogenesis has poles, determined from palaeomagnetic data, when plotted on come to mean "the folding of rocks in fold expanding Earth models, cluster as diametri- belts", not mountain-building. Confusion in cally opposed north and south poles. These the literature persists, however, and it is gen- pole locations show that the ancient North erally assumed that folding results from con- Pole was located in Mongolia to northern tinental collision, and collision results in mountain-building. In the real world, moun- China during the Precambrian and Palaeozoic eras, prior to moving north to its These pole locations tains ae eroded Plateaus ane a“ created by show that the Present Tocation as we coneinents migrated vertical movement and modified by erosion. . south. The ancient South Pole was locate esearchers have considered that because in western central Africa throughout the Researchers h; idered that b ancient North Pole | Africa throughout th Earth expansion is a radial process, then was located in Precambrian and Palaeozoic, prior to moving orogenesis caused by continental collision, south to its present location as the continents and hence mountain-building, cannot occur. Mongolia to northern migrated north. Earth expansion was then discounted China during the because the radial expansion process did not . appear to explain the compression Precambrian and required for continental collision, nor Palaeozoic eras the compression required for . . y orogenesis. prior to moving north On an expanding Earth, orogenesis to its present location as the continents means "folding of rocks to form fold migrated south. = What about space geodetics? Space geodetics is modern technolo- gy that uses VLBI (very long baseline interferometry), SLR (satellite laser ranging), GPS (global positioning sys- tems), DORIS (Doppler orbitography and radiopositioning integrated by satellite) and LLR (lunar laser ranging) to measure the dimensions of the Earth and plate motions of the continents to sub-centimetre accuracy. This technol- ogy has determined that the radius of the Earth is increasing by less than 5 + 3 mm/year, or in other words jown belts". During expansion, the continen- tal crust must distort, bend, twist and turn to adjust continuously for the change in surface curvature. During this crustal movement there is folding of the soft sediments within sedimenta- ry b , accompanied by faulting, volcanic intrusion and metamorphism to be "constant". This effectively (heating and compression of the rocks), replaces palaeomagnetics as the main resulting in orogenesis. Once the continents broke up and started argument against Earth expansion. to disperse during the Mesozoic era, the edges of the continents In order to determine Earth radius using VLBI, two or more started to rise as the interior collapsed during changing surface ground stations are used to determine Earth parameters in relation curvature. Throughout the world today, we now see great escarp- to a very accurate celestial reference frame. These measurements ment mountains along many of our continental margins, with no are then converted to an international terrestrial reference frame need for continental collision, and wide, relatively flat inland and used with measurements using satellite technology to calcu- plains. late a global solution. The limitations to all methods, and VLBI in particular, are atmospheric interference and, for the satellite 2 What about palaeomagnetics? methods, the use of the physical constants G (universal gravita- In palaeomagnetics, measurements of remnant magnetism tion) and M (Earth mass) to tie orbital parameters to the centre of residing in rocks containing iron minerals are made to determine _ the Earth. the ancient latitude of a site sample and the direction to the ancient When enough VLBI ground stations were established to form a magnetic pole. These measurements have long been considered global network during the early 1990s, it was found that the glob- the cornerstone of plate tectonics. They are routinely used to al excess in radius was 18 mm/year (Robaudo & Harrison, 1993). determine ancient pole positions to constrain reconstructions of | This value was considered to be extremely high when compared ancient continental assemblages, and have also been used to to expected deglaciation rates, estimated at less than 10 mm/year. These pole locations show that the | Mongolia to northern China ‘during the Palaeozoic eras, prior to moving north to its present location as the continents = What about palaeomagnetics? In palaeomagnetics, measurements of remnant magnetism residing in rocks containing iron minerals are made to determine the ancient latitude of a site sample and the direction to the ancient magnetic pole. These measurements have long been considered the cornerstone of plate tectonics. They are routinely used to determine ancient pole positions to constrain reconstructions of ancient continental assemblages, and have also been used to NEXUS 45 ancient North Pole was located in Precambrian and migrated south. OCTOBER — NOVEMBER 2000