地球科学 1788

《地球理论》

詹姆斯·赫顿

陆地本身并不长存——它被无尽地磨蚀、又重建，循环往复，时间没有起点，也没有终点。

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In depth · the introduction

你脚下的土地，曾经是海的底部——而总有一天，它还会再成为海底。

核心想法

赫顿凑近去看坚硬的岩石，发现它竟是由更古老岩石的碎屑——砂、贝壳、卵石——构成的：这些碎屑曾沉落在海底，后来变成了石头。所以陆地并非长存、并非最初就有。它是被回收再造的：今天的大陆，是用从前那些陆地磨损后的残骸堆起来的。

而且它一直在继续。河流把陆地磨成泥与沙；这些沉积物在海床上堆积；地球的内热把它烘成岩石，再把它顶回成新的山脉；接着雨与河又开始把它磨下去。如此循环往复，一个没有「关机键」的循环——而要让这循环运转足够多次、堆出我们眼前的世界，地球就必须老得无法想象。

那个在岩石里读出深时的农夫

詹姆斯·赫顿是苏格兰启蒙运动中人——受过医师训练，以务农与化工制造为业，是爱丁堡那个璀璨智识圈子里亚当·斯密（smith-1776）与詹姆斯·瓦特的朋友。几十年里看着泥土从自家田地上被雨水冲走，让他开始思索：失去的泥土都去了哪儿，新的陆地又从何而来。1785 年，他把自己的理论摆到了爱丁堡皇家学会面前；1788 年，他沿苏格兰海岸去寻找证据。在锡卡角，他和朋友们找到了：平铺的红砂岩层，横压在那截被锯断、被掀立起来、古老得多的灰色岩石的边缘之上——一整片悬崖里，叠着一个世界的两轮循环。他的同伴约翰·普莱费尔写道，望进时间的深渊望得那样远，人的心智「仿佛要发起晕来」。

它为何重要

在赫顿之前，欧洲多数人相信地球只有几千岁，而且很久以前一次成形。赫顿把「深时」交给了世界——让人意识到：过去浩瀚得几乎无法想象，看不到一个起点。仅此一念，就重塑了其后的一切。它让莱尔把地质学变成一门严谨的科学（lyell-1830）；它给了查尔斯·达尔文那片演化所需的、海洋般浩瀚的时间，去缓缓施展（darwin-1859）。后来几乎每一幅关于地球历史的图景，都立在赫顿铺下的这块地板上。

给大陆的一座堆肥堆

想象一座堆肥堆。你扔进枯叶与残渣；它们腐烂、下沉，化成肥黑的土；你把这土铺开，种出新的植物，植物死后又回到堆上。没有什么是永久的，可也没有什么被浪费——它只是在循环。赫顿看见整颗星球都这样运转，只不过把枯叶换成了岩石，把「季节」拉长到几百万年。山，并不是故事的结局；它们是等着变成堆肥的材料。

之前与之后

赫顿不是第一个注意到山岩里有海贝的人——尼古拉斯·斯坦诺早在 1669 年就立下了层状地层的诸原理——但他是第一个把这一切捆成一个运转着、由热驱动的循环，并要求一段几乎无限的过去的人。他自己的文字太过晦涩，这想法险些随他一同湮没；它得以存活，是因为约翰·普莱费尔在 1802 年把它清晰重述，也因为查尔斯·莱尔把它建进了那赢得地质学界的三卷书里（lyell-1830）。从那里，它径直奔向达尔文的演化（darwin-1859）；很久以后，放射性为赫顿的「深时」填上了真正的数字——约 45 亿年——而板块构造，终于解释了他只能用手指点、却无力解释的抬升（wegener-1912、hess-1962）。

The original document

Original source text

James Hutton (1726–1797) · “Theory of the Earth; or an Investigation of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe” · Transactions of the Royal Society of Edinburgh, Vol. 1 (1788)

The Earth as a machine

Hutton opens not with rocks but with purpose: the globe is a working machine, contrived so as to remain a fit habitation for living things — and to do so, it must repair itself as fast as it wears away.

When we trace the parts of which this terrestrial system is composed, and when we view the general connection of those several parts, the whole presents a machine of a peculiar construction by which it is adapted to a certain end.

The present land is made of the ruins of a former land

His first observation is the hinge of the whole theory. Look closely at the solid rock of the continents — sandstones, limestones, shales — and you find it built of sand, shells, and the worn debris of older rock: materials that once lay loose on the floor of the sea.

The solid parts of the present land appear, in general, to have been composed of the productions of the sea, and of other materials similar to those now found upon the shores.

Two operations: consolidation and uplift

For loose sea-floor sediment to become dry, solid land, two things are needed, and Hutton attributes both to the Earth's internal heat (his “Plutonist” stance, against the rival “Neptunists” who derived all rock from a universal ocean): first the consolidation of the loose materials into stone, and then the elevation of those consolidated masses from the bottom of the sea to the heights they now occupy. (Annotation of Hutton's argument.)

A circulation in the matter of the globe

Erosion destroys the land; consolidation and uplift build it anew. The two are not opposites but halves of one cycle — a circulation of matter that keeps the world habitable.

We are thus led to see a circulation in the matter of this globe, and a system of beautiful economy in the works of nature.

A succession of worlds

If today's land is built from the wreck of an earlier land, then that earlier land was itself built from one before it — and so on, a succession of former worlds, each recorded where new flat strata rest on the upturned, eroded edges of the old (an angular unconformity, which Hutton read in the field at Siccar Point in 1788).

But if the succession of worlds is established in the system of nature, it is in vain to look for any thing higher in the origin of the earth.

No vestige of a beginning

The cycle has run so many times, over a span so immense, that the rock record shows no first chapter and points to no last. Hutton claims no age in years — his point is precisely that the time is beyond measure.

The result, therefore, of our present enquiry is, that we find no vestige of a beginning,—no prospect of an end.

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Royal Society of Edinburgh · read 1785, published 1788 — expanded into Theory of the Earth, 2 vols., 1795