Possible relation between periodic glaciation and the flexure of the Galaxy

Abstract

At least five discrete episodes of widespread Earth glaciation or global cooling have occurred since late Precambrian time. A notable feature of such episodes is the ∼155-m.y. mean period of their mean ages, key dates being ∼770, ∼615, ∼445, ∼295, ∼145? and minus ∼10? m.y. B.P. Employing the following values for parameters of the Sun's galactic orbit, present circular velocity = 225 ± 25 km sec −1, present galactocentric distance = 9.0 ± 0.5 kiloparsec, and eccentricity = 0.1 ± 0.01, it is calculated as a first approximation that the period of the Sun's revolution around the galactic centre is 303 −51 +65 m.y. Assuming that the two galactic regions which appear to be tidally flexed by the Magellanic Clouds are stationary with respect to the galactic centre, then the mean period of solar passage between regions of given, diametrically-opposite galactic flexure is 152 −26 +33 m.y. Since the solar system now lies within a little-flexed region of the galactic disc, and the Earth is presently subjected to a climatic regime of high-latitude glaciation, it is suggested that passage through such regions may have resulted in the ∼155-m.y. rhythm of Earth glaciation since late Precambrian time.