Unit 3 Why Do We Believe That the earth Is Round Warm-Up Activity Can you prove that the earth is round? Go ahead and try! Will you rely on your senses or will you have to draw on the opinions of experts?Unit 3 Why Do We Believe That the Earth Is Round Warm-Up Activity: Can you prove that the earth is round? Go ahead and try! Will you rely on your senses or will you have to draw on the opinions of experts?