  How structures on various scales formed and evolved from the early Universe
up to present time is a fundamental question of astrophysical cosmology. EDGE
will trace the cosmic history of the baryons from the early generations of
massive star by Gamma-Ray Burst (GRB) explosions, through the period of cluster
formation, down to very low redshifts, when between a third and one half of the
baryons are expected to reside in cosmic filaments undergoing gravitational
collapse by dark matter (Warm Hot Intragalactic Medium: WHIM). In addition
EDGE, with its unprecedented observational capabilities, will provide key
results on several other topics. The science is feasible with a medium class
mission using existing technology combined with innovative instrumental and
observational capabilities on a single satellite by: a) observing with fast
reaction Gamma-Ray Bursts with a high spectral resolution (R ~ 500). This
enables the study of their (star-forming) environment from the Dark to the
local Universe and the use of GRB as back light of large scale cosmological
structures b) Observing and surveying extended sources (clusters, WHIM) with
high sensitivity using two wide field of view X-ray telescopes (one with a high
angular resolution and the other with a high spectral resolution).
