Liberals and Muslims have a lot in common. They are equally mixed up on the whole flat earth thing. Every time there is a dispute with liberals about science, liberals are quick to charge that those opposing their unsubstantiated claims are reverting to a belief in a flat earth even though no one of any reputation ever believed the earth was flat.
The mythology continues by the claim that Muslims were the first to discover the earth was round. Minister Fikri Işık claims that “Muslim scientists working around 1,200 years ago were the first to determine that the Earth is a sphere.”
There is absolutely no truth in this claim.
The flat earth myth was concocted by Washington Irving in 1828 in his two-volume biography of Christopher Columbus and picked up by others. In the eleven-volume Our Wonder World, first published in 1914, the editors offered the following undocumented claim: “All the ancient peoples thought the earth was flat, or, if not perfectly flat, a great slightly curving surface,” and “Columbus was trying to convince people that the earth was round.” ((Howard Benjamin Grose, ed., Our Wonder World, 11 vols. (Chicago: George L. Shuman & Co.,  1918), 1:1, 5.))
The Encyclopedia Britannica perpetuated the myth of a round-earth solution for Columbus’ voyages as late as 1961: “Before Columbus proved the world was round, people thought the horizon marked its edge. Today we know better.” The people knew better in Columbus’ day and thousands of years before him.
A 1983 textbook for fifth-graders misinformed students by reporting that Columbus “felt he would eventually reach the Indies in the East. Many Europeans still believed that the world was flat. Columbus, they thought, would fall off the earth.” ((America Past and Present (Scott Foresman, 1983), 98. Quoted in Jeffrey Burton Russell, Inventing the Flat Earth: Columbus and Modern Historians (New York: Praeger, 1991), 3.))
A 1982 textbook for eighth-graders claimed that Europeans “believed . . . that a ship could sail out to sea just so far before it fell off the edge of the sea. . . . The people of Europe a thousand years ago knew little about the world.” ((We the People (Heath, 1982), 28–29. Quoted in Russell, Inventing the Flat Earth, 3.))
Long before the 13th century, it was nearly a universal belief that that the earth was round. The best book on the subject is Jeffrey Russell’s Inventing the Flat Earth: Columbus and Modern Historians. It’s a devastating critique of the flat earth myth. The claim that Columbus had to convince the scientists and map makers of his day that the earth was round is pure fiction.
Long before Muhammad was a twinkle in his parents’ eyes, any idea of a flat earth had been dispelled. Russell points out the following:
“It must first be reiterated that with extraordinary few exceptions no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat.
“A round earth appears at least as early as the sixth century BC with Pythagoras, who was followed by Aristotle, Euclid, and Aristarchus, among others in observing that the earth was a sphere. Although there were a few dissenters — Leukippos and Demokritos for example — by the time of Eratosthenes (3 c. BC), followed by Crates (2 c. BC), Strabo (3 c. BC), and Ptolemy (first c. AD), the sphericity of the earth was accepted by all educated Greeks and Romans.
Nor did this situation change with the advent of Christianity. A few — at least two and at most five — early Christian fathers denied the sphericity of earth by mistakenly taking passages such as Ps. 104:2-3 as geographical rather than metaphorical statements. On the other side tens of thousands of Christian theologians, poets, artists, and scientists took the spherical view throughout the early, medieval, and modern church. The point is that no educated person believed otherwise.” ((Jeffrey Burton Russell, “The Myth of the Flat Earth,” Summary by Jeffrey Burton Russell for the American Scientific Affiliation Conference (August 4, 1997) at Westmont College.))
This means that Islam was rather late to the game if it was only around 1,200 years ago that Islam determined that Earth is a sphere. And it’s most likely they discovered this by reading the Greeks who had known this truth for centuries.