Columbus and other europeans of his time believed that the earth was
roughly 50 percent smaller than it really is.
roughly 50 percent larger than it really is.
about the same size as it really is.
just slightly smaller than it really is.

Columbus and other Europeans o his time believed that the Earth was roughly 50 percent smaller than it really is.

Explanation:

There were a few well-developed methods to measure Earth, the most influentials for Columbus and other Europeans of the era were the classical greeks ones and the Arabs method the one proposed by Posedinius found that the earth was at least 3/4 smaller than what Eratosthenes of Cyrene believed. The thing was that those perspectives were subject to debate and that the earth was smaller from what they believe was because civilization was challenging by nature, so they defied it. The Arab method suggested Posedinius was right about the measure, however, the Arab unit of distance was different from the Greek one and they realized the size was not certain. Those methods were impulsed by light, shadow, and calculations of distant objects. Those were minimized and challenged by the community. Leading them to believe that they were inaccurate at calculating the size of the earth and that the big quarter difference between the greeks classic and the distance difference between the Arab uni measure and the greek one were big enough to believe that the earth was at least 50% smaller than it is.

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