Milankovitch Cycles Theory & 冰山时期形成的原因

delan714

V1:
冰山时期形成的原因
第一段说M提出冰山时期是由于月球运动造成的，V支持这个观点，并且举了一个证据，这样很多人都接受了这个观点
第二段说有个人MM，他提出冰山时期是由于气候造成的
第三段说V在同意M观点的同时也部分的同意MM的观点

V2:
共3段。文章短，只有一屏。
开始讲有人认为是地球绕着太阳转导致北极有不同的日照时间，所以产生了periodical的Ice Age，即地球上冷暖时间交替。此理论被一个天文学家K什么提出来之后，又被一个海洋生物学家从海底沉积物发现的同位素衰减予以佐证。
第二段讲另外一个地理学家I什么在内华达的地下深水里做的试验的结果表明K的理论不对，因为根据I的同位素衰减结果，地球Ice Age的warm period时间应该是K推测的两倍长。
第三段讲一些科学家认为I的数据不对。然后K自己出来说话说I没有考虑到淡水和海水的取样不同造成的差异。所以关于Ice Age没有定论。

V3:
by catdog1124
有一个讲考察冰川时期，最开始一个科学家通过一种生物做实验，证明赤道在那时降温没有其他地方大。后来一个科学家出来说，用那种生物做实验不靠谱，因为那个生物不能很好显示极端的温差变化，然后科学家用珊瑚做实验，做出来结果差不多。

V4:
by alex6219 （690）
还有个第几篇也不知道了，说呀冰川时代赤道那边降温的事情，说是一开始认为赤道降的比一般的少好象，然后有个鸟人说是他用什么方法研究出来的呢？原来啊，用的某个叫F**的动物，额，反正是个生物，用他们的骨架子研究的，还搀和到什么SEDIMENT，我没好好看，好象有某题某选项里有SEDIMENT这个词语出现，我不管了最后。然后啊到了某某年，另一个鸟人就来了，他说这个研究不对啊，说是骨架子没不说明问题，对的，说骨架子不ACCURATE，然后他用了个在珊瑚里的化学物质，说是这个物质和该珊瑚所在的区域的水温是有关系的，记得一个题目，怎么问忘了，但很坏，文章里只说了化学物质DEPEND ON THE CHANGE OF海水温度，没说成正反比，然后有一选项说化合物随温度增加而增加，坏透坏透，我曾经被骗进了那么半分多钟

V5:
by babee2queen (v34)
冰川时期温差变化的实验
钩子写的很全，文章最后的方向是，第二组人做实验证明第一组人的实验不对。实际上全球温度变化是一样的。
有一个是用第二组人用什么证明第一组人做的是错的，定位文章中间位置
问题……实在是残念了……

V6:
by 崦嵫渺渺 (710)
是说什么冰河时期热带的温度下降的没有两极地区及其他地区快，探讨原因。一个科学家C做过一个调查，用热带地区海洋里的一种动物，什么什么的，没大看懂。后来人们发现的实际数据跟这个科学家预测的相悖，另外一个科学家G，又去做调查，根据C的方法，测量海洋里面的一种珊瑚里面的一种化学物质，得出一个什么结论。最后没时间了，大概看的，其他遇到的童鞋在补充吧。第一题是问G发现了什么的。后面忘了

V7:
by chenggong12 （710）
Ice age 关于热带温度两极温度下降的争论
内容机警很详细了,但问题挺绕的，都是推论题。
1．  C这个人的研究的结论不正确，跟一下那个选项有矛盾？
2．  从D(就是反对C的那个人)的研究可以推论出什么？

V8:
by dshimuro
我補一下, 文章只有一段, 開頭說一個scientist D(還是C?) 對於tropical region 那做了一個實驗, 結果說 tropical ocean 的溫度remains high, whereas其他地方的水在最近一次的 ice age 降了5度.  
而那個D用來研究溫度的媒介, 就是一種在tropical 海底的sediment (沉澱物), D的研究同時也反映了 tropical land和其他地方的land的溫度比較關係, 我沒細看這.
後來有一個recent study (沒說誰) 說溫度變化是universal的, 並非tropical 地區降溫比較少(也沒給解釋), 進而質疑了D的實驗(這邊重要).  基於這個原因, 另外一個scientist G 就著手往一個 Ba 開頭的海岸去找尋證據. 他用了一種coral 中的chemical sensitive to temperature. G 的實驗結果證實了再最近一次的溫度下降是universal.
題目有一題是說G的實驗結果證明了什麼?
選項有什麼ocean and land 溫度差多少多少啦, tropical land 和其他地方溫度怎麼樣啦, 不過都不是我選的, 因為文章沒有直接給.
我選了D, 說G的實驗證明了Ba那個海岸的海水in fact cooled.  我肯定. 這個是以最少的文章資訊能得到最broad的答案.
另外一題說recent study 說明了D的研究的什麼:
有一個干擾選項: D’s study is inaccurate because the sediment used 還是什麼的. 那個不對, 文章沒有給這個inaccurate的形容詞.
我選了, D’s study is limited it can not support a hypothesis about ocean water 還是類似的.

V9:
by linkoo07
冰川时代温差变化（最后一题问第二个学者的研究indicate了什么，我选的是什么海水cool off减慢了某钟海洋生物的成长

V10:
by chenxiaomiao(740)
1.第二个科学家G的实验infer什么，我选了E 说temperature cooling 会让珊瑚生长缓慢什么的。但现在又琢磨着不太对了，文中只是说珊瑚跟temperature有关，但没说是变慢……
2.第一个科学家的结论为什么是problematic 这个我比较确定，选的是因为跟existing finding矛盾，因为原文说了since1976好多别的studies就说他不对了，A选项是说他认为热带比别的地方 cool less，跟prior 1976之前的观点比，我觉得不对，文中没说之前的研究吧
3.主旨：我选的compare两种观点，有个选项是advocate后者，但我觉得作者没有明确态度支持谁
最后一篇时我其实时间非常充裕，但心里像有把火在烧似的就是静不下心读，不然寂静能再好一点

V11:
原来观点认为：在冰川期，热带气温下降的少，其他地方下降多。
一个人从植物角度发现：热带气温下降多
另一个人从化学角度发现：某东西的化学浓度显示在冰川期，热带气温下降非常多。
结论：热带气温与其他地方同步下降。


V12:
1976年某个人的观点认为在ice age期间tropic的温度没有象其他地方那样变化大。这个人是通过对tropic ocean中某种生物的研究得出的结论。因为这种生物的骨骼是temperature sensitive的。但是后来人们对tropic land的chemical substance的研究发现至少tropic land的温度是和其他地方一样变化大的。最后说现在另外一个人开始怀疑1976年观点所基于的论据了。说可能那种生物的骨骼不是temperature sensitive的。
?  
V13:
然后还有一篇很长很长的是讲冰川的.第一段基本不考(大家大概扫扫好了,这文章有一屏半), 全是highlight的第二段.大意就是有一个专家提出了一个理论研究冰川的layer可以计算出时间还是什么的.第二段有人提出质疑,通过什么新的技术证明专家说的不对(有一个题目提到highlight的theorist起什么作用),但是1970年又有人重新做了research,发现其实质疑是错误的,于是还专家一个清白(有一道题目就是问1970年的研究做什么了,我觉得貌似应该是revise专家的提议).还有主旨题目.

V14:
第一段：1920年，一个科学家M.M.（首字母）提出一个Claim/Theory说貌似地球的Orbit和Ice Age有关系。他的证据是在一些（可能是南北极的）冰川Layer里面发现了一些植物的标本。
第二段：但是到了1950年，有一个根据CO2的研究指出M.M.的理论有问题，貌似指出问题的关键也是植物的标本问题。后来1970年研究技术更新之后，通过新技术表明，M.M.的理论还是可以被接受的~

V15:
冰川那一篇。说M发现通过什么东西可以考证冰川的年代  而且这个东西受地球自转的影响。而且冰川会在世界各地周期性出现（澳大利亚除外，这里看似重要，但是没考）  
后来第二段有科学家用新的 carbon dating技术推翻了他的结论，很多细节 完全没看懂   最后1970年以后一个什么技术的出现又还了M一个清白

V16:
有一个讲考察冰川时期，最开始一个科学家通过一种生物做实验，证明赤道在那时降温没有其他地方大。后来一个科学家出来说，用那种生物做实验不靠谱，因为那个生物不能很好显示极端的温差变化，然后科学家用珊瑚做实验，做出来结果差不多。

V17:
by babee2queen (v34)
冰川时期温差变化的实验
钩子写的很全，文章最后的方向是，第二组人做实验证明第一组人的实验不对。实际上全球温度变化是一样的。
有一个是问第二组人用什么证明第一组人做的是错的，定位文章中间位置

V18:
第一段介绍这个paradox，第二段好像试图carbon oxide解释这个东西，第三段是说有一个科学家提出了一个假设，但是另外一些科学家反驳了这个假设。
记得有个题目是说该文章提供了以下哪条信息，我选择的是有“glacier”的那个……记不大清楚了~
还有个题目是说文章第一段提***（忘记了，不好意思）有什么用，我选择的是“帮助定义该paradox”

V19:
太阳的发光, 地球的冰川。（呵呵，只记得关键词和“一屏半”的长度了）最后一段是某人的学说。但是，该学说被最近的research发现了flaw (有题：问最后一段的结构)

V20:
by chenggong12 （710）
Ice age 关于热带温度两极温度下降的争论。内容机警很详细了,但问题挺绕的，都是推论题。
C这个人的研究的结论不正确，跟一下那个选项有矛盾？
从D (就是反对C的那个人)的研究可以推论出什么？

V21:
第一段说M提出冰山时期是由于月球运动造成的，V支持这个观点，并且举了一个证据，这样很多人都接受了这个观点
第二段说有个人MM，他提出冰山时期是由于气候造成的
第三段说V在同意M观点的同时也部分的同意MM的观点
这个也是很长，但是结构比较清晰

V22:
by linkoo07
冰川时代温差变化（最后一题问第二个学者的研究indicate了什么，我选的是什么海水cool off减慢了某钟海洋生物的成长）

V23:
讲的是冰川时代的什么模型的错误。很简单。先说一个人的观点，第一段最后一句话有个题问。第二段一个人又提出一个。最后一段，一个人又说是数据的问题。（这里有题）。实在想不起来了，想起来补充

V24:?
第一段讲M的理论多牛B，第二段讲50年代的什么试验证明M是错的，然后第二段的后半部分又说原来50年代的试验方法（还是数据？）是错误的，这样的话M的理论又被证明是对的了。

V25:
1976年某个人的观点认为在ice age期间tropic的温度没有象其他地方那样变化大。这个人是通过对tropic ocean中某种生物的研究得出的结论。因为这种生物的骨骼是temperature sensitive的。但是后来人们对tropic land的chemical substance的研究发现至少tropic land的温度是和其他地方一样变化大的。最后说现在另外一个人开始怀疑1976年观点所基于的论据了。说可能那种生物的骨骼不是temperature sensitive的。

V26:
1920某科学家M提出一个理论认为地球orbit和冰川layer有关。证据是冰川中发现的植物标本
1950，基于二氧化碳的研究表明M理论是错的
1970，研究技术革新之后，认为M理论可以被接受。

V27:
第三个RC就是JJ提到的, 可惜提的太少, 而且我看完文章了才发现是jj, 说一个M的研究人员认为冰川的变迁是由于地球的轨道变化引起来的, 后面说1950年一个人通过研究岩层的放射性画出时间轴推翻了这个M的人的预期, 结果最近有发现1950年做的实验数据有问题, 新的实验正好支持M这个人的预期, 因此他的理论又被接收.
这个题的问题的确比较难, 都是建立在对全文的把握上的. 有一道是问如果1950年的实验数据没问题会怎么样, 我选了就会让人们怀疑M的理论

V28:
冰山并不像原来理论推测的那样不变，会逐渐消减。提出了2个原因

V29:
有一道说冰川融化的。第一段是说本来融化的冰川汇入海洋之后会通过降雪再回到雪地上。因此海洋中水不会更多。然而一个satellite什么的发现western Atlantic 的情况不是这么回事。第二段，一个研究者和她助手去研究这个现象，发现两个原因，第一个不记得，第二个说水面之下会有flint (类似的单词)。第三段举了个例子说另一个地方B的情况。证明了温室效应会使海平面上升。
题目有：那个研究者研究是为了干什么？我选的是给出一个解释。有主题题，选了有Discrepancy不符合(之处)，不一致(之处)这个词的一项。

V30:
冰川应该是分三段，
第一段说南极的冰川受气候变暖影响化了，
第二段好像是有个科学家检验了一个什么flow还是什么的，
第三段就是总结说气候变暖导致了那个中间因素使得冰川化了。
题目第一道是细节题，后面还有道主旨题，我选的时候都挺纠结的，问题出在定位完了找答案不太像，确实记的不太清，不好意思

V31:
old Antarctica南极洲冰河是stable
但衛星照片發現是有變化的(decline)
某人&colleagues去研究可能的explanation
發現融化的水會使lubrication上升,導致冰河變化
in 2002 Ruth-B 冰棚collapse
支持冰河是有變化的

V32:
第二篇文章就是那个关于冰川的，但是和jj里面讲的似乎都不一样，是说旧的观点认为，北极的冰川应该是固定不变的就是说每年融化的冰川，比如飘到海里的iceberg，又会被降雪所补偿。但是卫星拍到的画面，又确实证明了北极的冰川在缩小，这是什么原因呢？
说虽然冰川的底部和空气的温度是隔开的isolated的，但是，因为最底层和岩石的摩擦（这里有个题），会产生一些stream，冰流，然后会造成冰川下面的湖溢出，然后然后冰流会越来越大。
因为全球变暖，温室效应，这个冰川会继续融化，可能会造成更多的崩塌之类的。
文章不长，不到一屏，问题有主题题，说文章讲的是什么，有冰流的作用和潜在的后果，还有为什么有一天冰川会彻底崩塌等等。我选的是冰流的作用和潜在的后果，也不是很确定。还有就是冰流怎么形成的，原因，我选的是那个摩擦。

V33:
第二篇是change in earth orbit. 第一段讲M的理论多牛B，第二段讲50年代的什么试验证明M是错的，然后第二段的后半部分又说原来50年代的试验方法（还是数据？）是错误的，这样的话M的理论又被证明是对的了。

delan714

1：
地球轨道根数变化与第四纪冰期 Changes of the Earth's Orbital Elements and the Quaternary Glacial Epoch
米兰柯维奇(Milankovitch)天文气候学理论和第四纪地质时期以来冰期的研究进展.研究结果表明,地球上的冰体积具有近10万yr的变化周期,并伴有近4万yr和2万yr的变化周期,它们是由于地球的轨道根数变化导致的气候变迁所致;不同的地球物理资料中均存在上述类似的变化周期,表明气候变迁所导致的变化是全球性效应,证实米兰柯维奇天文理论是基本正确的。
2：
At the recent American Geophysical Union meeting in San Francisco, the 25th anniversary of one of the great papers in paleoclimatology was celebrated. The paper, entitled “Variations in the Earth’s orbit: Pacemaker of the Ice Ages,” presented important new evidence supporting the orbital theory of glaciation. Orbital theory goes back over a century but is most closely associated with Milankovitch, who calculated the effects of gravitational perturbations on the seasonal cycle of Earth’s insolation (the radiation incident at the top of the atmosphere). Insolation varies on several time scales, including ~20,000 years (termed precession), ~40,000.
在最近举行的美国地球物理联合会在旧金山会议上，在古气候伟大的报纸之一的25周年庆祝。该文件，题为“变化中的地球轨道：冰河时代的心脏起搏器”，提出了重要的新证据支持他们的冰川轨道理论。轨道理论可以追溯到一个多世纪，但最密切的米兰科维奇，谁计算地球的日照季节性周期的影响引力扰动在大气顶层（辐射事件有关）。暴晒几个不同时间尺度上，包括?2.0万年（称为岁差），?40,000。



Milankovitch Cycles Theory背景知识

http://forum.chasedream.com/GMAT_Math/thread-424461-1-1.html

delan714

Causes of Ice Ages

1.  Geologists have shown that for about 80 percent of the past 2.5 million years, ice-age conditions have prevailed on the Earth's surface. During the past one million years, increased glacial conditions have run in cycles of approximately 100,000 years.  

2.  Many different factors may contribute to these increases in glaciation at regular intervals throughout Earth's more geologically recent history. The three most prominent factors probably relate to the amount of sunlight that reaches the Earth. This varies over time for three main reasons. First, the planet wobbles as it spins, due to the pull of the sun and moon. Furthermore, the Earth tilts on its axis and the degree of tilt changes over time. Finally, the orbit of the Earth around the sun is elliptical and the length of the major axis of the ellipse changes over a period of about 100,000 years. A mathematician named Milutin Milankovitch discovered in the 1930s that the pattern of insolation, or sunlight, predicted by these eccentricities in the Earth's movement matched the period of the last several eras of intense glaciation.

3.  These Milankovitch insolation cycles were the dominant theory in ice-age research for much of the twentieth century despite the fact that the match between periods of peak insolation and most intense glaciation were not exact. For example, a cycle of 400,000 years predicted by the Milankovitch theory has never shown up in the climate records obtained through the study of microfossils deposited on the sea floor. Also, recent analysis has shown that the insolation theory predicts peaks of sunlight at intervals of 95,000 and 125,000 years. Climatological data do not support this predicted sunlight peaking. Other damaging evidence was the indication of a precisely measured sudden rise in temperature at a water-filled cave in Nevada, which preceded the increase in solar radiation that was supposed to cause it.

4.  These and other problems with the Milankovitch cycles led some researchers to seek alternative explanations for the cyclic arrival of extended ice ages. In the 1990s, it was discovered that the orbital inclination of the Earth to the sun and planets could also be responsible for climate changes. If we imagine a flat plane with the sun in the center and the planets revolving around it, the Earth slowly moves in and out of the flat plane by a few degrees, repeating the cycle every 100,000 years. Two scientists, Muller and MacDonald, have proposed that it is this orbital inclination which is ultimately responsible for the periods of glaciation and warming. They argue that because of the oscillation振动, the Earth periodically travels through clouds of debris, in the form of dust and meteoroids. Such debris could reduce the amount of solar energy reaching the surface of our planet, thus plunging it into regular cold periods.

5.  The advantage of this theory is that it is not confronted with several of the problems associated with the Milankovitch theory. In particular, the new theory fits well with the analysis of ocean sediments taken from eight locations around the world. This analysis yielded data clearly showing the peak of the last several ice ages with a period of 100,000 years and corresponding to the periods when the Earth's oscillating inclination takes it through clouds of extraterrestrial debris.

6.  However, many researchers in this field are not yet persuaded by the inclination hypothesis. The main problem is that the amount of dust that falls to the ground when the Earth travels through space debris is relatively small - not enough to produce radical climate changes. Volcanic eruptions, for example, release much greater amounts of ash and dust and have relatively little effect on climate. Supporters have countered that the by-products created by the dust as it vaporizes on entering the atmosphere cause subtle changes to the energy levels. Nevertheless, the necessary physical proof has yet to be found to convince the skeptics

Questions

1. The word "prevailed" in the passage is closest in meaning to
a) ruled
b) existed
c) survived
d) triumphed

2. What can be inferred from paragraph 2 about the factors that contribute to glaciation冰河作用?
a) They affect the Earth’s spin.
b) They are geologically recent.
c) Only three factors relate to levels of sunlight.
d) Other factors than those relating to the sunlight affect ice buildup.

3. The phrase "these eccentricities" in the passage refers to all of the following EXCEPT
a) the various movements of the Earth as it spins.
b) the degree of change in the Earth’s tilt over time.
c) the pattern of insolation matching the Earth’s movement
d) the changing distance to the sun during the Earth’s elliptical orbit

4. Scientists accepted the Milankovitch theory even though
a) the peaks of sunlight occurred at intervals of 95,000 and 125,000 years.
b) the peaks of insolation and intense glaciation did not match.
c) there were climate records of a 400,000-year cycle.
d) there were micorfossil deposits on the sea floor.

5. In paragraph 4, why does the author suggest the image of a flat plane?
a) To help the reader visualize the positions and movements of the heavenly bodies.
b) To demonstrate to the reader how the Earth orbits the sun.
c) To support the argument that the orbital inclination increases tilting.
d) To show how the Milankovitch theory doesn’t explain the cyclical changes in climate.

6. The word "it" in paragraph 4 refers to
a) such debris
b) solar energy
c) the surface
d) our planet

7. In paragraph 4, the author explains that
a) Milankovitch did not know about the orbital inclination of the Earth.
b) glaciation occurs when the orbital inclination has entered a new cycle
c) the Earth always travels through clouds of debris after moving out of the plane by a few degrees
d) the amount of solar energy reaching the Earth’s surface casues the changes of temperature.

8. What problems in the Milankovitch theory was mentioned as being explained by the Muller and MacDonald theory?
a) The climate records obtained by studying microfossil deposits not matching his predicted cycle.  
b) The irregularities of the Earth’s movements through orbital inclinations not following any pattern.
c) The Earth’s spin wobbling in relation to the Earth’s oscillating inclination.
d) The peak in the ice ages occurring at intervals between 95,000 and 125000 years instead of 400,000.

9. The word "persuaded" in the passage is closest in meaning to    
a) convinced
b) discouraged
c) affected
d) challenged  

10. What problem is associated with the Muller and MacDonald theory?
a) The amount of debris that is released from volcanoes is proportional to the amount of interstellar dust.
b) The amount of ash from volcanoes and space dust that vaporizes in the atmosphere is too small.
c) The amount of dust entering the atmosphere is less than the amount of ash and dust released by volcanoes.
d) The by-products created by vaporized space dust cause relevant changes to the energy levels.
 

Many different factors may contribute to these increases in glaciation at regular intervals throughout Earth's more geologically recent history. nThe three most prominent factors probably relate to the amount of sunlight that reaches the Earth. This varies over time for three main reasons. First, the planet wobbles as it spins, due to the pull of the sun and moon. nFurthermore, the Earth tilts on its axis and the degree of tilt changes over time. nFinally, the orbit of the Earth around the sun is elliptical and the length of the major axis of the ellipse changes over a period of about 100,000 years. nA mathematician named Milutin Milankovitch discovered in the 1930s that the pattern of insolation, or sunlight, predicted by these eccentricities in the Earth's movement matched the period of the last several eras of intense glaciation.

11. Look at the four squares [n] that indicate where the following sentence can be added to the passage.
 When the Earth is at its furthest from the Sun, less sunlight reaches the surface.
 Where would the sentence best fit?

12. Directions: Select the appropriate phrases from the answer choices and match them to the flaws in the ice-age theories to which they relate. TWO of the answer choices will NOT be used. This question is worth 4 points.

Answer Choices a) Data of climate records not coinciding with predicted intervals of sunlight b) Temperature rises occurring before the increase of sunlight c) The irregularities of the Earth’s movement during its orbit around the Sun. d) The inconsistency between the periods of sunlight and glaciation. e) The relatively mild effect of volcanic eruptions on the climate. f) The orbital inclination of Earth through clouds of debris. g) The relatively small amount of interstellar debris reaching Earth. h) The lack of clear support from ocean sediment data. i)  The lack of physical evidence in support of the effects of the inclination hypothesis.

Flaws in the Milankovitch Cycles Theory   l l           l           l           Flaws in the Muller and MacDonald Theory   l l   l

running2k

ding

delan714

Milankovitch Cycles Theory
Milankovitch Theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milankovi?. Milankovi? mathematically theorised that variations in eccentricity, axial tilt, and precession of the Earth's orbit determined climatic patterns on Earth, resulting in 100,000-year ice age cycles of the Quaternary glaciation over the last few million years. The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 23,000-year cycle between the seasons and the orbit. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Currently, this angle is 23.44 degrees and is decreasing.

The Milankovitch theory of climate change is not perfectly worked out; in particular, the largest observed response is at the 100,000-year timescale, but the forcing is apparently small at this scale, in regard to the ice ages.[1] The frequency modulation[2] or various feedbacks (from carbon dioxide, cosmic rays or from ice sheet dynamics) explain this discrepancy.

Milankovitch-like theories were advanced by Joseph Adhemar, James Croll and others, but verification was difficult due to the absence of reliably dated evidence and doubts as to exactly which periods were important. Not until the advent of deep-ocean cores and a seminal paper by Hays, Imbrie and Shackleton, "Variations in the Earth's Orbit: Pacemaker of the Ice Ages", in Science, 1976,[3] did the theory attain its present state.
Milankovitch cycles theory is about the frequency of ice age. Milankovich proposed that the temperature of earth has something to do with the position of the earth in the orbit around sun. However it did not gain acceptance until 1968 when Dr. Imbrie presented additional evidence for M theory. He measured the isotope level in small seashell deposit and the change of isotope abundance corresponds with the temperature change.

However, later on, a geochemist tested the samples from Devil's Hole, a place in south Nevada and the results did not match with the previous results.
Even thought Dr. Imbrie still think M theory was valid, he conceded that many other factors contribute to the isotope level. It may be why the results did not match.

Can We Date the Ice Ages?
Following improvements in the ability to measure isotope ratios which came about as a spin-off of the wartime Manhattan project, physical chemist Harold Urey began to examine the possibility that the ratio of the two principal isotopes of oxygen found in the atmosphere might provide a clue as to past temperatures. It was based on the idea that the ratio of the heavier isotope (oxygen-18) to the more prevalent isotope (oxygen-16) found at the sea surface would change depending on the temperature of the ocean water near the surface. Urey thought that a careful study of the oxygen isotope ratio in the shells of sea creatures, which build their calcium carbonate shells from oxygen available in the seawater, might serve to indicate the temperature of the water in which they formed. During warmer periods, it was thought, evaporation from the ocean surface would tend to enrich the sea surface water with the heavier isotope of oxygen.

Perhaps, Urey reasoned, the isotope ratios found in the layers of discarded shells of sea organism which form the ocean bottom could thus serve as a record for the past temperatures of the ocean.
The theory is fraught with many ifs, but it was pursued with persistence, starting in the 1950s, by Italian-educated micro paleontologist Cesare Emiliani, a one-time collaborator of Urey at the Argonne Laboratory then associated with University of Chicago. Emiliani identified certain species of small shell-forming sea organisms known as foraminifera有孔虫类, which he thought suitable for oxygen-isotope analysis to determine past climates. The conclusions he drew as to the dating of the ice ages were constantly challenged by leading oceanographers, who found them in contradiction with their studies of ocean bottom cores海底内核学说. The method was also attacked on the grounds that it wasn't clear that the creatures formed their shells壳, known as tests, near enough to the surface to reflect changes in isotope ratios.


p.s.:
Quaternary glaciation：第四纪
一段地质时期，距今180万年至现代。第四纪继第三纪之后，是两个新生代中较近的一个。划分为更新世和全新世。第四纪的特征是气候在全球规模上有大的周期变化。这些变化引起了广大地区遭到冰盖的反复侵袭，所以这个纪常被称为大冰期。从生物学看，第四纪的主要特点是人类的进化和扩散。第四纪气候和环境的激烈变化引起了特别是哺乳类的迅速演化和灭绝。大型哺乳动物的灭绝可能也同当时人类领土的迅速扩大有关。
Earth’s movements
As the Earth spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Although the curves have a large number of sinusoidal components, a few components are dominant[1]. Milankovitch studied changes in the orbital eccentricity, obliquity, and precession of Earth's movements. Such changes in movement and orientation change the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Changes near the north polar area are considered important due to the large amount of land, which reacts to such changes more quickly than the oceans do.

4mmgirl

厉害厉害