Milankovitch Cycles and Glaciation

Milankovitch Cycles and GlaciationAlthough the history of glaciation during the Pleistocene epoch (2 million to10,000 years ago) is well established, we do not know with complete certaintywhy glaciation takes place. For over a century, geologists and climatologistshave struggled with this problem, but it remains unsolved.It is long known that Earth’s orbit around the Sun changes periodically,cyclically affecting the way solar radiation strikes the Earth, but the idea thatthese changes affect climate was first advanced by James Croll in the late1800s. Later, Milutin Milankovitch elaborated the theory with calculations thatconvincingly argued that the cycles, now known as Milankovitch cycles, couldcause climatic variations.The word “elaborated” in the passage is closest in meaning toA.correctedB.defendedC.studiedD.developedAccording to paragraph 2, Milankovitch was the first to do which of thefollowing?A.Introduce the idea that periodic changes in Earth’s orbit couldinfluence Earth’s climateB.Show that periodic changes in Earth’s orbit could be mathematicallycalculatedC.Provide calculations to show that periodic changes in Earth’s orbitcould affect Earth’s climateD.Propose that Earth’s orbit is not fixed but undergoes periodic changesThe Milankovitch cycles emerge from the way three cyclic changes in Earth’sorbit combine. One characteristic of Earth’s orbit is its eccentricity, the degreeto which the orbit is an ellipse rather than a circle. Changes in the eccentricityof Earth’s orbit occur in a cycle of about 96,000 years. The inclination, or tilt, ofEarth’s axis also varies periodically, moving between 22 degrees and 24.5degrees. The tilt of Earth’s axis, toward the Sun at some times of the year andaway from the Sun at other times, is responsible for the annual cycle ofseasons. The greater the tilt, the greater the contrast between summer andwinter temperatures. Changes in the tilt occur in a cycle 41,000 years long.Also, Earth wobbles as it spins, like a slightly unsteady top. The wobble cycleis completed once every 21,700 years. Changes in eccentricity, tilt and wobbledo not affect the total amount of solar radiation Earth receives in a year, butthey do affect how evenly or unevenly this radiation is disturbed over thecourse of a year. According to the Milankovitch theory, about every 40,000years the three separate cycles combine in such a way that the differencebetween summer and winter temperatures is at a minimum. At this point wintertemperatures are milder but so too are summer temperatures. As a result, lessice is melted in the summer than is formed in the winter, so glaciers build upand a period of glaciation results.According to paragraph 3, Milankovitch’s theory holds that periods of glaciationresult from a particular combination of changes in all the following EXCEPTA.the shape of Earth's orbitB.the inclination o...