(CN) – Evidence found in a 90 million-year-old layer cake of sedimentary rock in Colorado may confirm a critical theory of how planets in our solar system behave in their orbits around the sun.
The discovery, made by researchers from the University of Wisconsin-Madison and Northwestern University, presents the first hard proof of what scientists call the “chaotic solar system,” a theory proposed in 1989 to account for minor variations in the present conditions of the solar system.
These variations play out over millions of years, and produce drastic changes in planetary climate – changes that can be reflected in rocks that offer a glimpse into Earth’s history.
The team analyzed alternating layers of shale and limestone laid down over millions of years in an ancient North American seaway, at a time when dinosaurs still roamed the planet. The research led to the team to identify an 87 million-year-old signature of a resonance transition between Earth and Mars – a phenomenon that occurs when two orbiting bodies occasionally tug at one another.
Subtle variations in a planet’s orbit can lead to major changes to the location and orientation of a planet relative to the sun. This can also impact the amount of solar radiation a planet receives, which is a key driver of climate.
“The impact of astronomical cycles on the climate can be quite large,” co-lead author Stephen Meyers said. “Astronomical theory permits a very detailed evaluation of past climate events that may provide an analogy for future climate.”
Meyers, a professor of geoscience at UW-Madison, specifically noted the spacing of Earth’s ice ages, which match periodic changes in the shape of the planet’s orbit.
In order to find the signature of a resonance transition, the team reviewed geological records in what is known as the Niobrara Formation in Colorado. The formation was created over tens of millions of years as sediment was deposited on the bottom of the Cretaceous Western Interior Seaway, a shallow ocean that stretched from what is now the Arctic Ocean to the Gulf of Mexico.
“The Niobrara Formation exhibits pronounced rhythmic rock layering due to changes in the relative abundance of clay and calcium carbonate,” Meyers said. “The source of the clay (laid down as shale) is from weathering of the land surface and the influx of clay to the seaway via rivers. The source of the calcium carbonate (limestone) is the shells of organisms, mostly microscopic, that lived in the water column.
“Climate change influences the relative delivery of clay versus calcium carbonate, recording the astronomical signal in the process.”
The research confirms the theory proposed in 1989 by astronomer Jacques Lasker, after numerical calculations of the outer planets in our solar system showed Pluto’s “chaotic” orbit.
“Other studies have suggested the presence of chaos based on geological data,” Meyers said. “But this is the first unambiguous evidence, made possible by the availability of high-quality, radioisotopic dates and the strong astronomical signal preserved in the rocks.”