The ice starts keeping records
Antarctic ice from this point onward still exists — and still holds the air of the time.
- When
- —
- Duration
- 26 thousand years
- Known to
- ± 20 thousand years
- Era
- Early Pleistocene, Quaternary
The deepest continuous Antarctic ice cores, from EPICA Dome C, reach back roughly 800,000 years, and older ice recovered from blue-ice areas extends further still. Bubbles trapped in that ice are physical samples of the ancient atmosphere, giving direct measurements of carbon dioxide and methane rather than proxies. Everything before this is inferred; from here the record is, in the most literal sense, preserved. Those cores show carbon dioxide oscillating between roughly 180 and 300 parts per million across every glacial cycle — and never once approaching today's value.