I would like to add that there has never, not once, in the entirety of human civilization, been a recorded even of a person falling over the edge of the earth. That is at least 4000 years, probably more.
Now one arguement you might propose is:
"Well that's because if you fell off, you couldn't tell anyone now could you?"
Maybe so. But in order to fall off, you need to first scale this supposed 150ft ice wall. To do that you would certainly need the help of one or more persons, not to mention the effort to get to this ice wall. So even though the person that actually went over could not tell of his fate, there would be at least one witness who could. Yet, with the exception of myths and fictional stories, there are NO historical accounts of this happening, ever.