This paper proposes a conjecture about special values of L-functions of
geometric motives over Z. We conjecture the following: the pole order of the
L-function L(M, s) of M at s=0 is given by the negative Euler characteristic of
motivic cohomology of $D(M) := M\dual(1)[2]$. Up to a nonzero rational factor,
the L-value at s=0 is given by the determinant of a pairing coupling an
Arakelov-like variant of motivic cohomology of M with the motivic cohomology of
D(M). Under standard assumptions concerning mixed motives over Q, finite fields
and Z, this conjecture is essentially equivalent to the conjunction of
Soul\'e's conjecture about pole orders of $\zeta$-functions of schemes over Z,
Beilinson's conjecture about special L-values for motives over Q and the Tate
conjecture over F_p.