There's much we don't understand about Godzilla.
His titanic size has always been problematic. As Danielle Venton sumarizes over at Popular Science, the monster's most recent incarnation would weigh in at 164,000 tons and boast bones twice as strong as some titanium alloys.
Consider the example of the spherical cow -- not an adversary of mighty Gojira but rather a fitting scientific metaphor: As this cow grows, its volume increases more rapidly than its surface area. Double the radius and you see a 4x surface area increase and an 8x volume increase. You can't take a small form, make it bigger and expect it to function the same -- that goes for giant gorillas as well as God lizards that grow in size from 50 meters to 150 meters without significant morphological changes.
But as R. McNeill Alexander points out in "Engineering limits to the body size of land animals," it's less about what's morphologically or biologically possible, but more about what's competitive in the struggle for existence.
Of course, Godzilla and his fellow Massive Unidentified Terrestrial Organisms (MUTO) are not denizens of our word. As pointed out in the latest franchise installment, these titans are radiation-feeding leftovers from a primal terrestrial era.
Eater of Rads
Interestingly enough, a radiation-eating (radiovore?) Godzilla would not be alone in our natural world. In 2007, researchers at the Albert Einstein College of Medicine of Yeshiva University discovered that some fungi use radioactivity as an energy source as well.
In "Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi," the researchers found that fungi containing the pigment melanin can utilize the ionizing radiation portion of the electromagnetic spectrum to transform radioactive energy into biological energy. This would be in keeping with the way the chlorophyll in plants converts sunlight into bio-energy.
Reports of melanin-rich fungi thriving on Chernobyl's reactor walls inspired the research, but the possible applications extend far beyond. The researchers suggest that radiation-grown fungi might one day feed human space travelers, or even unlock the possibility that melanin in human flesh provides energy to skin cells.
But of course Godzilla is an unnatural creature, ultimately alien to our world of natural biology. What's more, he might truly be a god. Film producer Sh?go Tomiyama stated the following in a 2004 interview with the now-defunct PennyBlood.com (archived here):
How can science seek to explain such a being?
Monster of the Week is a - you guessed it - regular look at the denizens is of our monster-haunted world. Sometimes we'll focus on the cultural aspects, but mostly we'll look at the possible science behind a creature of myth, movie or legend. Be sure to explore the Monster Gallery as well as the Monster Science video series.