The Crepuscular Earth presented here is a guess reference model of the planet in which all mineral resources have been extracted and dispersed and fossil fuels have been burnt. It serves as a realistic limit of resources to assess the Earth's non-renewable exergy capital. Under such conditions we estimate a state of the atmosphere and hydrosphere using updated fossil fuels stocks (1925 GtC for proven reserves, rising to about 16,224 GtC when including estimated additional reserves) and emissions projections in a simple model of the carbon cycle. We consider the BAU-I scenario as the most likely to occur, corresponding to an atmospheric injection of about 2000 GtC. Accordingly, we propose a crepuscular atmosphere having a carbon dioxide content of 683 ppm, a mean surface temperature of 17 degrees C (peak carbon dioxide induced warming of 3.7 degrees C above pre-industrial temperatures), a pressure of 1.021 bar, and a composition in volume basis of 78.8% N-2, 20.92% O-2, 0.93% Ar, and 0.0015% of trace gases. Considering that oceans account for 97.5% of the whole hydrosphere, the crepuscular hydrosphere is assumed to have the current chemical composition of the oceans at an average temperature of 17 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.