That added uncertainty makes it even harder for astronomers to forecast more than 50 million years into the past, to correlate temperature anomalies in the geological record with possible changes in the Earth’s orbit. That knowledge would be useful as we try to understand climatic changes underway today. About 56 million years ago, Dr. Kaib said, the Earth evidently went through the Paleocene–Eocene Thermal Maximum, a period lasting more than 100,000 years during which average global temperatures increased as much as 8 degrees Celsius.
Was this warm spell triggered by some change in Earth’s orbit around the sun? We may never know.
The paper is here