About 23 million years ago, a huge ice sheet spread over Antarctica, temporarily reversing a general trend of global warming and decreasing ice volume. Now a team of researchers has discovered that this climatic blip at the boundary between the Oligocene and Miocene epochs corresponded with a rare combination of events in the pattern of the Earths orbit around the Sun. Researchers show the transient glaciations and other climatic variations in the Earths orbit known as Milankovitch cycles. Although the concept of such relationships is not new, some of the results were surprising. The astrophysicist Milutin Milankovitch first proposed that cyclical variations in certain elements of Earth-Sun geometry can cause major changes in Earths climate. The main variables are eccentricity, obliquity, and precession. Eccentricity refers to the changing shape of Earths orbit around the Sun, which varies from nearly circular to elliptical over a cycle of about 100,000 years. Obliquity refers to the angle at which Earths axis is tilted with respect to the plane of its orbit, varying between 22.1 degrees and 24.5 degrees over a 41,000 year cycle. And precession is the gradual change in the direction Earths axis is pointing, which completes a cycle every 21,000 years. Because there are several components of orbital variability, each with lower frequency components of amplitude modulation, there is the potential for unusual interaction between them on long timescales of tens of millions of years. The result of this rare congruence was a period of about 200,000 years when there was unusually low variability in the planets climate, with reduced extremes of seasonal warmth and coldness. Earths orbit was nearly circular, so its distance from the Sun stayed about the same throughout the year. In addition, the tilt of Earths axis, which gives rise to the seasons, varied less than usual.
1. The primary purpose of the passage is to
A. Discuss temperature fluctuations in the Antarctica.
B. Question the validity of the cyclical hypothesis.
C. Explain how earth-sun geometry affects climate.
D. Propose a new method to estimate the age of the earth.
E. Summarize research findings in astrophysics.
2. If the assertions in the passage are true, which of the following must also be true?
A. The shape of the Earths orbit around the Sun doesnt remain constant.
B. The Earths orbit around the sun remained elliptical most of the time in the history of Earth.
C. The shape of the Earths orbit varies with the changes in the Earths axis.
D. Unusual interactions between the components of orbital variability occur in hundreds of millions of years.
E. It is impossible to predict the actual causes that result in the tilting of the earths axis.
3. According to the passage, the factors that contribute to climatic change is/are
I. The changing shape of earths orbit.
II. The angle at which the earths axis is tilted.
III. Lack of change in the directions the Earths axis is pointing.
A. II only B. I and III C. II and III D. I and II E. I, II, III
4. It can be inferred from the passage that, an unusual interaction between components of orbital variability results in which of the following?
A. Maximum variation in climate.
B. Extreme warmth or coldness.
C. The tilting of Earths axis varied more than usual.
D. Unusually low change in climatic conditions.
E. The Earths orbits becoming elliptical.
Ans.
1-c
2-a
3-d
4-d
