  The possibility of planetary mass black hole production by crossing entropy
limits is addressed. Such a possibility is given by pointing out that two
geophysical quantities have comparable values: first, Earth's total negative
entropy flux integrated over geological time and, second, its extensive entropy
bound, which follows as a tighter bound to the Bekenstein limit when entropy is
an extensive function. The similarity between both numbers suggests that the
formation of black holes from planets may be possible through a strong
fluctuation toward thermodynamic equilibrium which results in gravothermal
instability and final collapse. Briefly discussed are implications for the
astronomical observation of low mass black holes and for Fermi's paradox.
