Read this and answer the question. If the question is unanswerable, say "unanswerable".

Immanuel Velikovsky is an example of a recent scientific exoheretic; he did not have appropriate scientific credentials or did not publish in scientific journals. While the details of his work are in scientific disrepute, the concept of catastrophic change (extinction event and punctuated equilibrium) has gained acceptance in recent decades.

What medium did Immanuel Velikovsky not publish his works in that is accepted practice?
scientific journals