So a comet's mass is not sufficient enough to store the required heat for life or liquid water even if it has a short periodic orbit around our sun. Could life not exist within these constraints, even if it meant a period of hibernation? Perhaps when the comet's orbit increases or decreases its' distance from the sun, freezing and thawing would cause periods of thriving life or hibernation?
There are two questions here:
1. "Could life exist under these conditions?"
2. "Could diatoms exist under these conditions?"
We don't even have to find a perfect answer to #1 in order to give a firm "NO" to #2.
And #2 is what the claim is consisting of. It's clearly bogus.