万物简史 第612期:冰河时代(9)

Part of the problem was that Croll's computations suggested that the most recent ice age occurred eighty thousand years ago, whereas the geological evidence increasingly indicated that Earth had undergone some sort of dramatic perturbation much more recently than that. Without a plausible¹ explanation for what might have provoked an ice age, the whole theory fell into abeyance². There it might have remained for some time except that in the early 1900s a Serbian academic named Milutin Milankovitch, who had no background in celestial³ motions at all—he was a mechanical engineer by training—developed an unexpected interest in the matter. Milankovitch realized that the problem with Croll's theory was not that it was incorrect but that it was too simple.

在一定程度上，问题在于克罗尔的计算认为，最后一次冰川期出现在8000年前，但是地质学证据越来越表明，地球在比3000年近得多的一段时期内曾经历过某种严重的摄动。不对造成一个冰川时代的原因作出合理的解释，整个理论就没法站住脚。要不是一位名叫米卢廷·米兰柯维契的塞尔维亚学者的出现这个问题本来会存在一段时间。米兰柯维契根本没有研究天体运动的背景——他是一个训练有素的机械工程师——但他在20世纪初突然对这一问题产生了兴趣。他发现，克罗尔的理论的问题并不是它不正确，而是它太简单。

As Earth moves through space, it is subject not just to variations in the length and shape of its orbit, but also to rhythmic⁴ shifts in its angle of orientation⁵ to the Sun—its tilt⁶ and pitch and wobble—all affecting the length and intensity⁷ of sunlight falling on any patch of land. In particular it is subject to three changes in position, known formally as its obliquity⁸, precession, and eccentricity⁹, over long periods of time. Milankovitch wondered if there might be a relationship between these complex cycles and the comings and goings of ice ages. The difficulty was that the cycles were of widely different lengths—of approximately 20,000, 40,000, and 100,000 years, but varying in each case by up to a few thousand years—which meant that determining their points of intersection¹⁰ over long spans of time involved a nearly endless amount of devoted¹¹ computation. Essentially¹² Milankovitch had to work out the angle and duration of incoming solar radiation at every latitude¹³ on Earth, in every season, for a million years, adjusted for three ever-changing variables.

地球在空间运动时，不仅轨道的长度和形状会有所变化，而且朝向太阳的角度——它的倾斜度、偏侧度和离心度，也会有规律地发生变化，所有这些都影响了照射到地面任何一点的阳光的时间长度和强度。尤其是，地球在漫长的时间内要经历三种位置变化，即所谓的黄道交角、岁差和偏心度。米兰柯维契觉得，这些周期性的复杂变化与冰川期的产生和消退也许存在某种关系。困难在于，这种周期性交化的时间跨度相差过大——有的大约2万年，有的4万年，还有的10万年，差不多每个周期的差别都长达几千年——这就意味着，要想确定它们在漫长的时间段里的交叉点，必须经过几乎是无休止的精心演算。最主要的是，米兰柯维契必须计算出，100万年来，随着上述三种因素的不断变化，阳光在每一季节照射地球上每一纬度的角度和持续时间。

1 plausible   

adj.似真实的，似乎有理的，似乎可信的

参考例句：

• His story sounded plausible.他说的那番话似乎是真实的。
• Her story sounded perfectly plausible.她的说辞听起来言之有理。

2 abeyance   

n.搁置，缓办，中止，产权未定

参考例句：

• The question is in abeyance until we know more about it.问题暂时搁置，直到我们了解更多有关情况再行研究。
• The law was held in abeyance for well over twenty years.这项法律被搁置了二十多年。

3 celestial   

adj.天体的；天上的

参考例句：

• The rosy light yet beamed like a celestial dawn.玫瑰色的红光依然象天上的朝霞一样绚丽。
• Gravity governs the motions of celestial bodies.万有引力控制着天体的运动。

4 rhythmic   

adj.有节奏的，有韵律的

参考例句：

• Her breathing became more rhythmic.她的呼吸变得更有规律了。
• Good breathing is slow,rhythmic and deep.健康的呼吸方式缓慢深沉而有节奏。

5 orientation   

n.方向，目标；熟悉，适应，情况介绍

参考例句：

• Children need some orientation when they go to school.小孩子上学时需要适应。
• The traveller found his orientation with the aid of a good map.旅行者借助一幅好地图得知自己的方向。

6 tilt   

v.(使)倾侧；(使)倾斜；n.倾侧；倾斜

参考例句：

• She wore her hat at a tilt over her left eye.她歪戴着帽子遮住左眼。
• The table is at a slight tilt.这张桌子没放平，有点儿歪.

7 intensity   

n.强烈，剧烈；强度；烈度

参考例句：

• I didn't realize the intensity of people's feelings on this issue.我没有意识到这一问题能引起群情激奋。
• The strike is growing in intensity.罢工日益加剧。

8 obliquity   

n.倾斜度

参考例句：

• It is here that the obliquity factor makes a crucial difference. 正是在这里，倾斜因子构成了重要的差别。 来自辞典例句
• The obliquity of the ecliptic is the fundamental cause of the seasons. 黄道的倾角是季节的基本成因。 来自辞典例句

9 eccentricity   

n.古怪，反常，怪癖

参考例句：

• I can't understand the eccentricity of Henry's behavior.我不理解亨利的古怪举止。
• His eccentricity had become legendary long before he died.在他去世之前他的古怪脾气就早已闻名遐尔了。

10 intersection   

n.交集，十字路口，交叉点；[计算机] 交集

参考例句：

• There is a stop sign at an intersection.在交叉路口处有停车标志。
• Bridges are used to avoid the intersection of a railway and a highway.桥用来避免铁路和公路直接交叉。

11 devoted   

adj.忠诚的，忠实的，热心的，献身于...的

参考例句：

• He devoted his life to the educational cause of the motherland.他为祖国的教育事业贡献了一生。
• We devoted a lengthy and full discussion to this topic.我们对这个题目进行了长时间的充分讨论。

12 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。

13 latitude   

n.纬度，行动或言论的自由(范围)，(pl.)地区

参考例句：

• The latitude of the island is 20 degrees south.该岛的纬度是南纬20度。
• The two cities are at approximately the same latitude.这两个城市差不多位于同一纬度上。