A period between ice ages known as Stage 11, which occurred about 450,000 years ago, is of particular interest because the Earth's orbit at that time is believed to have been very similar to its orbit today.
Would you happen to know how the similarity of Earth's present orbit to a prior period's orbit is determined?
Orbits are mathematically predictable ... in both directions. Using a bit of calculus, astronomers can pretty much determine the configuration of any orbit for any time period. I've got a cheapy astronomy program on my machine at home that generates night skies for any date and time over the past several thousand years and into the future several thousand years.