In Russia's extreme north, a widening chasm known as the Batagaika Crater provides a unique opportunity to study the past.
Early declassified satellite images recorded the crater's growth in the 1960s and 1970s followed by multispectral sensor imagery captured by Landsat and Sentinel satellites, building a continuous view over the last 60 years. But the gash in the ground offers an opportunity to study much further back in time.
Each exposed layer of the crater wall is like a geological snapshot, helping scientists understand the past climate of the permafrost. The layers at the bottom could be as old as 650,000 years.
Declassified satellite imagery, Landsat, and Sentinel imagery are available for free download at the USGS EarthExplorer website.