No, that was never the concensus among scientists. Scientific consensus is a valid argument in the same sense that "extraordinary claims require extraordinary

No, that was never the concensus among scientists. Scientific consensus is a valid argument in the same sense that "extraordinary claims require extraordinary proof"; the probability that mainstream science is wrong and you are right is low, proportionally to the amount of science at either end. The fact that the Earth is round was known by the Greeks and has been acknowledged ever since, not least following several circumnavigations by people such as Magellan. The notion that people (scientists and laymen alike) believed in a flat earth is really a popular myth perpetrated, probably, to make the Columbus story more interesting. Columbus knew perfectly well that the Earth was round. The fact that Earth and the universe are very old was pretty much agreed upon since the 18th century with the arrival of geology as a branch of science. Aristotle thought the universe was infinite in age. The Hindus thought it was billions of years old. The 6000 year thing is a very recent Christian idea.