A team of astrophysicists have shown that from approximately two billion years ago until 600 million years ago, an atmospheric tide driven by the sun countered the effect of the moon, keeping Earth’s rotational rate steady and the length of day at a constant 19.5 hours. Credit: Kevin M. Gill
The paper’s authors include Norman Murray, a theoretical astrophysicist with U of T’s Canadian Institute for Theoretical Astrophysics ; graduate student Hanbo Wu, CITA and Department of Physics, U of T; Kristen Menou, David A.
“Sunlight also produces an atmospheric tide with the same type of bulges,” says Murray. “The sun’s gravity pulls on these atmospheric bulges, producing a torque on the Earth. But instead of slowing down Earth’s rotation like the moon, it speeds it up.” Murray and his collaborators relied on geologic evidence in their study, like these samples from a tidal estuary that reveal the cycle of spring and neap tides. Credit: G.E. Williams