Sedimentary rocks laid down when a great seaway ran through the middle of North America have demonstrated that Mars has helped shape Earth's climate. A transition in the relationship between the orbits of Earth and Mars occurred while dinosaurs still dominated the Earth, providing support to a theory of the way planetary orbits shift.
Materials deposited on the floor of what is known as the North American Seaway provide a record of Earth's climate during the Cretaceous era. Depending on the conditions of the day the rocks were either shale or limestone.
Professor Stephen Meyers of the University of Wisconsin, Madison, carefully dated the alternating layers of each in the Niobrara Formation, Colorado, to provide a record of the period's changing climate. “Imagine a very warm and wet climate state that pumps clay into the seaway via rivers, producing a clay-rich rock or shale, alternating with a drier and cooler climate state which pumps less clay into the seaway and produces a calcium carbonate-rich rock or limestone,” Meyers said in a statement.
Meyers argues in Nature that the changes were so regular they must have been driven by alterations to Earth's orbit.
We know that orbital patterns known as Milankovitch cycles have been responsible for swings between glacial and interglacial conditions over the last few million years. These are a result of three things: Shifts between a more rounded and more elongated (or eccentric) orbit, the tilt of the Earth's axis, and the season in which Earth is closest to the Sun.
Meyers claims that during the Cretaceous, Martian gravity helped determine the first of these.