Answer
-3
Work Step by Step
Based on the definition of the common logarithm, we know that $log(x)=log_{10}x$.
Furthermore, recall that $log_{b}x=y$ is equivalent to the statement $b^{y}=x$ (where $x\gt0$, $y$ is a real number, and $b\gt0$ and $b\ne1$).
Therefore, $log(.001)=log_{10}.001=-3$, because $10^{-3}=\frac{1}{10^{3}}=\frac{1}{1000}=.001$.