There is a hole 3,270 metres deep in the ice of East Antarctica. Each year's snow buries the last, so every metre down is older. At the bottom, the ice fell as snow 800,000 years ago, and it still holds air from that time.
The core that came out of it stands on the left, drawn from what was measured at each depth, with the lab's records beside it. It starts with the top 120 metres. The red line is where you are: scroll, and it goes down.
scroll down
Report · the same core, unrolled
Now read it by age
Down the hole, the old ice is squeezed thin, so the early ice ages flash past. Here the same measurements are laid out with every year given the same width: 800,000 years ago on the left, today on the right.
Show these numbers as a table
Why the last 150 years look different
air from ice coresair measured directly (Mauna Loa, Hawaii)
The ice-core part of this chart comes from Law Dome, near the Antarctic coast, where far more snow falls than at Dome C. There the air is sealed in within decades, so the record reaches almost to the present and overlaps the direct measurements.
Why the bottom of the core holds most of the time
What is simplified
The core on the left is drawn, not photographed. Its colour at each depth comes from the records: snow and firn from the density, milkiness from the bubbles (gone between about 600 and 1,300 m), and grey from the dust. Ice-age ice really does carry cloudy layers, but they are faint; here the more dust was measured, the greyer the core is drawn. Firn density is a smooth curve fitted through about 350 kg/m³ at the surface and 830 kg/m³ at 100 m.
The picture changes scale once. Down to the depth where the air is sealed in, it shows only the top 120 m. After that it shows the whole hole at one scale, with the rock under it.
The close-ups are drawn too, with bubbles shown far bigger and fewer than life (real ones are a fraction of a millimetre across, hundreds to a cubic centimetre).
The orange spikes are chemistry, not something you could see. A big eruption leaves a layer of sulfate, found by melting the ice and measuring it. Visible ash layers are rare in this core. The sulfate record used here has been published only down to 2,094 m.
In the thin slices the crystal size is the measured average at that depth (110 to 3,100 m), and the colours are worked out from how ice bends polarised light in a slice 0.45 mm thick. Which crystal points which way is random, with the scatter narrowing with depth the way the measured crystal directions do.
Temperature is the classic reading of the heavy-hydrogen record: the difference from the last 1,000 years at Dome C. A 2021 study using other methods finds that the last ice age was 4 to 7 °C colder there, not 9. The shape of the curve is not in doubt; the size of the swings is.
Dates are the AICC2012 time scale. Near the surface it can be decades out, and at the bottom several thousand years. A newer scale (AICC2023) shifts some of the deep ages by a few thousand years.
The CO₂ trace joins several Antarctic cores (Dome C, Vostok, Law Dome and four others) into one record, placed at the Dome C depth that holds air of the same age. Dome C itself has no sealed air above about 100 m.
Two flags are not about this core: the 1889 lead comes from sixteen other Antarctic cores, and the fallout layers of 1955 and 1965 from snow pits. Their depths here are worked out from the time scale.
Crystal size: EPICA Dome C grain radius data, NOAA World Data Service for Paleoclimatology (2004). The data files for all of the above are at ncei.noaa.gov/pub/data/paleo/icecore/antarctica.