By measuring the radioactive decay of atmospherically produced ³⁶Cl and ¹⁰Be in an ice core drilled in West Antarctica, we were able to determine the age of the deepest sample close to bedrock to be about 550 thousand years old. This means that the ice in this location, known as Skytrain Ice Rise, has survived several warm periods in the past, at least since marine isotope stage 11.