The image above shows rock formations within the Petrified Forest National Park in Arizona. It was from deep within the rock formations shown here that scientists extracted a 518-metre-long core sample that proved the correlation between variations in Earth’s orbit, and long-term climate changes on Earth.
Scientists have associated major changes in Earth’s climate with periodic changes in the path Earth follows around the Sun for almost a century, and knew that while these shifts in Earth’s orbit were largely caused by the combined gravitational effects of the planets Jupiter and Venus, there was never any hard, direct evidence to prove the supposition. Scientists also knew that the last five major geological periods- the Triassic, Jurassic, Cretaceous, Cenozoic epochs, and one major ice age, the Pliocene-Quaternary glaciation, had occurred as the result of the Milankovitch Cycles.
These cycles include a 100,000 year cyclical change in the eccentricity of Earth’s orbit, a 41,000 year cyclical change in Earth’s axial tilt relative to the plane of its orbit, and a 21,000 year cyclical change in the orientation of the Earth’s axis. All of these cycles have contributed to major impacts on plant and animal life, as well as on the evolutionary paths of many species throughout Earth’s history.
However, the Milankovitch Cycles represent only half of the story. The other half involves the effects of these cycles when they are combined with regular-as-clockwork 405,000-year cyclical variations in Earth’s orbital eccentricity caused by Venus and Jupiter- variations that vary from a nearly perfectly circular orbit, to an eccentricity of about 5%, which necessarily affects the amount of sunlight that falls on Earth over very long timescales.
Viewed objectively, the above amount to only circumstantial evidence, since the effects of the cycles on Earth’s climate could only be positively linked to planarity motions over the last 50 million years or so, and could be confirmed only for the last 215 million years. Proving the link between variations in Earth’s orbit and regular, major changes in the global climate therefore required hard evidence from deep within the earth itself.
In a recent study, named “Empirical evidence for stability of the 405-kiloyear Jupiter–Venus eccentricity cycle over hundreds of millions of years” that appeared in the journal ‘Proceedings of the National Academy of Sciences of the USA’, the team of investigators describe how they found this evidence in a 518-metre-long rock core sample. The sample included material from between 202 to 253 million years ago, which represents the Triassic period.
In simple terms, the investigators linked known reversals of Earth’s magnetic field to parts of the rock core samples that included zircons (minerals that contain uranium and which can be used for radioactive dating), as well as to accepted evidence in the fossil record that prove major climatic changes. To verify their findings, the known reversals of Earth’s magnetic field were also compared to sections of the rock core sample that do not contain zircons, and what emerged was incontrovertible evidence that the 405,000-year cycle represents the most stable astronomical pattern or cycle that affects Earth’s orbit, and hence, its climate. Moreover, the results also show that this cycle had been stable for at least several hundred million years, and that it is still in operation today.
While none of this research is likely to have a direct bearing or influence on the lives of most of Earths’ population, one researcher, Professor Kent, explained that-“Scientists can now link changes in the climate, environment, dinosaurs, mammals, and fossils around the world to this 405,000-year cycle in a very precise way.”
As a practical matter from a purely scientific perspective, the implications of this research are profound, since it allows scientists to put improved and more accurate, if not yet precise, constraints on not only climatological and geological timelines, but also on the evolution of the solar system than was possible to do before this research. The practical advantage of this is that if we were to base the search for life outside of the solar system purely on what is known about life on Earth, our improved understanding of how life evolved and adapted to changing climatic conditions on Earth will also improve our understanding of how life might have evolved and adapted elsewhere in the Universe.