Ancient alien theory grew out of the centuries-old idea that life exists on other planets, and that humans and extraterrestrials have crossed paths before.
The theme of human-alien interaction was thrust into the spotlight in the 1960s, driven by a wave of UFO sightings and popular films like 2001: A Space Odyssey.
This article collects evidences that place a lower limit on the age of the Universe beyond the 6,000 to 10,000 years asserted by most Young Earth creationists (YECs) and the literalist Ussher chronology.
All of this evidence supports deep time: the idea, considered credible by scientists since the early 1800s, that the Earth (and the Universe) is millions or billions of years old.
There are three standard creationist responses: First, creationists assert that current rates (Y) are different than past rates.
Radiometric dating is self-checking, because the data (after certain preliminary calculations are made) are fitted to a straight line (an "isochron") by means of standard linear regression methods of statistics.
By looking at past concentrations of greenhouse gasses in layers in ice cores, scientists can calculate how modern amounts of carbon dioxide and methane compare to those of the past, and, essentially, compare past concentrations of greenhouse gasses to temperature. Ice cores have been drilled in ice sheets worldwide, but notably in Greenland and Antarctica[4, 5].
* Solar variation at 65°N due to en: Milankovitch cycles (connected to 18O). Ice core records allow us to generate continuous reconstructions of past climate, going back at least 800,000 years.
Modern science accepts that the Earth is about 4.54 billion years old and the entire universe is around 13.77 billion years old.
These limits usually take the form: "Because we observe [X], which occurs at rate [Y], the universe must be at least [Z] years old".