The image shows a cross section of the Greenland Ice Sheet, where a recent study by MacGregor et al. have mapped the layers imaged by radar. Thanks to ice core measurements the age of the layers have been determined, and in the image the layers from the Holocene period (the past 11.700 years) are shown in green. The ice formed during the last ice age, that spanned 11.700 to 115.000 years ago are coloured blue, and finally, the ice from the last interglacial, the Eemian period, more than 115.000 years ago, are red. The grey areas show parts where the age is unknown.
For more details see:
MacGregor et al., 2015, Journal of Geophysical Research
For more beautiful visualisations of the data:
NASA’s Scientific Visualization Studio