We estimate the energy density epsilon pile-up at mid-rapidity in central Pb+Pb collisions from 1 - 200 GeVucleon. epsilon is decomposed into hadronic and partonic contributions. A detailed analysis of the collision dynamics in the framework of a microscopic transport model shows the importance of partonic degrees of freedom and rescattering of leading (di)quarks in the early phase of the reaction for E-lab greater than or equal to 30 GeVucleon. The energy density reaches up to 4 GeV/fm(3), 95% of which are contained in partonic degrees of freedom. It is shown that cells of hadronic matter, after t approximate to 2R/gamma, can be viewed as nearly chemically equilibrated. This matter never exceeds energy densities of similar to 1 GeV/fm(-3), i.e. a density above which the notion of separated hadrons loses its meaning. [References: 28]
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