231. In addition to other artworks, figurines representing the human female in exaggerated form have also been found at Upper Paleolithic sites. It has been suggested that these figurines were an ideal type or an expression of a desire for fertility.
232. Continued sedimentation—the process of deposits’ settling on the sea bottom—buries the organic matter and subjects it to higher temperatures and pressures, which convert the organic matter to oil and gas.
233. As muddy sediments are pressed together, the gas and small droplets of oil may be squeezed out of the mud and may move into sandy layers nearby.
234. Both oil and gas are less dense than water, so they generally tend to rise upward through water-saturated rock and sediment.
235. When the well reaches a pool, oil usually rises up the well because of its density difference with water beneath it or because of the pressure of expanding gas trapped above it.
236. Water or steam may be pumped down adjacent wells to help push the oil out.
237. The development of the oil field on the North Slope of Alaska and the construction of the Alaska pipeline are examples of the great expense and difficulty involved in new oil discoveries.
238. Offshore drilling platforms extend the search for oil to the ocean’s continental shelves—those gently sloping submarine regions at the edges of the continents.
239. It may be in a pool too small or too far from a potential market to justify the expense of drilling.
240. Offshore platforms may also lose oil, creating oil slicks that drift ashore and foul the beaches, harming the environment.
