Who would think the Bible teaches that the Earth floats in space?
See Job 26:
God stretches the northern sky over empty space and hangs the earth on nothing. - Job 26:7
Of course, the purpose of all these lines in Job are to show Job his ignorance and insignificance compared to God, not to be science lessons.
Eratosthenes (276194 BC) estimated Earth's circumference around 240 BC. He had heard that in Syene the Sun was directly overhead at the summer solstice (the bottom of a well being completely illuminated) whereas in Alexandria well bottoms were still in shadow.
Using the differing angles the shadows made as the basis of his trigonometric calculations he estimated a circumference of around 250,000 stades. The length of a 'stade' is not precisely known, but Eratosthenes' figure only has an error of around five to fifteen percent. Eratosthenes used rough estimates and round numbers, but depending on the length of the stadion, his result is within a margin of between 2% and 20% of the actual meridional circumference, 40,008 kilometres (24,860 mi). Eratosthenes calculation of the circumference of the Earth was only valid through the aassumption that the distance to the Sun was so great that the rays of sunlight would essentially be parallel.
The spherical nature of the Earth was assumed for centuries prior, however, nobody had ever rationalized the belief rigorously.
Exactly.