Is the Earth contracting?

Abstract

Summary. The fossil record of the vanation of the solar day and the synodic month with geological time is examined for evidence of the steady contraction of the Earth postulated by Lyttleton to explain a discrepancy between the apparent secular accelerations of the Sun and Moon. Data for the Phanerozoic and the Precambrian agree in showing that a change in the Earth's moment of inertia as large as that suggested by Lyttleton is only consistent with the fossil record if the secular change in the gravitational constant G/C 2 + 4 x 10-/yr. A variation of G of this magnitude appears to be ruled out by a recent analysis of lunar occultation observations utilizing Atomic Time. In a recent analysis of the apparent secular accelerations of the Sun and Moon Lyttleton (1976) has suggested that a discrepancy between observation and the predictions of tidal theory first noted by Jeffreys (1929) may be explained by a steady decrease in the Earth's moment of inertia i/Z = - 8 x lO-/yr. This observation lends support to the phasechange hypothesis (Ramsey 1948; Lyttleton 1965) in which the continued evolution of the Earth's liquid tore leads to a global contraction of order 0.1 mm/yr and a change in the moment of inertia consistent with that required to reconcile the astronomical observations. In this paper I shall discuss whether a contraction of the Earth of this magnitude is consistent with the lengths of the tropical year and the synodic month deduced from the growth patterns found in fossil bivalves, corals and stromatolites. I shall show that the fossil data probably rule out changes in the Earth's moment of inertia as large as those required to resolve the discrepancy between the lunar and solar accelerations.