Solution
= Solution
Using the same diameter convention and <viscosity> estimate,
$$
\boxed{\frac{\rho^2g\lambda^3}{\eta^2}
\simeq\frac{(3000)^2(9.81)(6.0\times10^6)^3}
{(2.56\times10^{21})^2}
\simeq2.9\times10^{-15}.}
$$
Geometrical factors omitted in the scaling do not affect the conclusion: \b[<inertia> is negligible]. Convective <inertia> is smaller still by the small relief-to-wavelength ratio. <Mantle> creep is extremely slow despite the large length scale.