Terrascope is a Google Earth implementation of the LANDSAT MSS, TM and ETM+ ortho mosaics for the 1970s, circa 1990 and circa 2000. It is designed to allow rapid comparison of LANDSAT imagery between these periods for any view in Google Earth. The imagery is provided as superoverlays in which resolution (level of detail) increase as you zoom in on an area. Full resolution is 57 metres/pixel for the 1970's (MSS), 28.5 metres/pixel for the circa 1990 (TM) and 14.25 metres/pixel for circa 2000 (ETM+). The rationale for terrascope is to provide an easy mechanism for visual change detection for non remote-sensing specialists who may be interested in environmental change research (desertification, land use change, urbanisation, coastal fluvial and water body change), awareness raising (of hotspots for habitat loss for example), and conservation monitoring or prioritisation uses.