Oil exploration. When searching for gold, measurements of g can be used to find regions within the Earth where the density is larger than that of normal soil. Such measurements can also be used to find regions in which the density of the Earth is smaller than normal soil; these regions might contain a valuable fluid (oil). Consider a deposit of oil that is 300 m in diameter and just below the surface of the Earth. For simplicity, assume the deposit is spherical. Estimate the change in the acceleration due to gravity on the surface above this deposit. Assume the density of the oil is 800 kg/m³ and the density of normal soil and rock is 2000 kg/m³. Companies that search for valuable minerals actually use this method.