A theory explaining ice ages must also address the fact that during the Pleistocene IceAge (2.6 million to 11,700 years ago) several intervals of glacial expansion separated by warmerinterglacial periods occurred. At least four major episodes of glaciation have been recognized inNorth America, and six or seven glacial advances and retreats occurred in Europe. Theseintermediate-term climatic events took place on timescales of tens to hundreds of thousands ofyears. The cyclic nature of this most recent episode of glaciation (i.e., during the Pleistocene) haslong presented a problem in formulating a comprehensive theory of climatic change.2. The word “comprehensive ”in the passage in meaning toA: complete B: convincing C: well supported D: widely accepted3. According to paragraph 3, which of the following is a fact that theories about ice ageshave had difficulty explaining?A: The Pleistocene was separated from the previous ice age by a long interval of mild climate.B: During the Pleistocene Ice Age, glacial advances and retreats alternated in a cyclic pattern.C: There have been notably fewer episodes of glaciation in North America than in Europe.D: The Pleistocene Ice Age gave way to milder climate about 10,000 years ago.

Over the last 700,00 years, how many glacial periods have there been?

Paragraph5: Milankovitch attributed the onset of the Pleistocene Ice Age to variations in threeparameters of Earth's orbit. The first of these is orbital eccentricity, which is the degree that Earth'sorbit departs from a perfect circle in its orbit around the Sun. The orbit varies from nearly a circle toan ellipse (an oval-shaped, elongated circle) and back again in about 100,000 years. Thiscorresponds closely to 20 warm-cold climatic cycles that occurred during the Pleistocene. Thesecond parameter is the angle between Earth's axis and a line perpendicular to the plane of theecliptic (the path along which the Sun appears to move). This angle shifts about 1.5 degrees duringa 41,000-year cycle. The third parameter relates to another complicated movement pattern with a23,000-year cycle. Milankovitch proposed, and now many scientists agree, that the interaction ofthese three parameters provided the triggering mechanism for the glacial-interglacial episodesduring the Pleistocene.5. The word “this” in the passage refers toA: the variation in three parameters of Earth’s orbitB: the amount of time it takes for Earth to orbit around the SunC: the length of the Pleistocene AgeD: the variation of Earth’s orbit from a circle to an ellipse and back to a circle

around 1310 C.E. Europe went into a climactic phase known as the "Little Ice Age"?Group of answer choicesTrueFalse

(Q020) Recent studies of ice agesGroup of answer choicesreveal fewer ice ages and less complexity than was originally thought.have identified paleosols that form during glacial periods.have identified glacial events by analyzing oxygen-isotope ratios in marine sediments.suggest that the entire Earth was covered by glacial ice in the Pleistocene.

A: It has been extremely difficult for scientists to identify the causes of glaciation because most iceages occurred millions of years ago and left behind little geologic record.B: Some scientists have noted similarities between long-term and short-term climatic cycles of thePleistocene.C: Changes within the Sun itself are known to have a major influence on the amount of solarradiation received at any given latitude on Earth.D: Long-term glaciation is most likely caused by the movement and interaction of Earth's plates.E: The Milankovitch theory uses variations in Earth's rotation and orbit to explain the cyclicoccurrence of glacial periods that last tens to hundreds of thousands of years.F: Volcanic activity and variations in solar energy have been proposed but not established ascauses of climatic events that are hundreds of years long. It has been extremely difficult forscientists to identify the causes of glaciation because most ice ages occurred millions of years agoand left behind little geologic record.