Reflections on Geologic Time, The Problem with Granite vol. I

Da Vinci and Steno's observations and conclusions about the nature of fossils concerned layered rocks, rocks formed from particles ("sediment") that are moved about by common processes active at the Earth's surface: gravity, wind, water, and ice. There was, of course, another problem. How did granite form?

Whiston and Burnet were proponents of explanations consistent with Biblical accounts. Aristotle had advocated that knowledge was rational and independent of the senses; it was to acquired by reasoning, intuition, and revelation of the innate properties of things. This approach was very successful at preserving the knowledge of books that had survived the Middle Ages and presented a consistent picture. Fossils were in the rocks because they had always been there; fossils on mountaintops were consistent with the Biblical account of a global flood. However, Da Vinci and Steno were neither satisfied nor complacent with the status quo and these renegades relied, instead, on what they could observe.

This division between what is known or knowable and what can be observed had a profound effect on infant science. The rationalist approach of Aristotle was on its way to the wings while Rene Descartes (1596-1650) and empiricism took center stage. Descartes advocated a method of doubt and argued propositions should not be accepted until logically proven. What you could see and touch took precedence over intellectual reasoning alone.

Abraham Gottlob Werner (1750-1817) was the leading Neptunist of the time. He advocated the idea that granite had crystallized from minerals in Earth's early oceans. He based much of his reasoning on Whitson's 1696 book, New Theory of the Earth and assumed the inerrantcy of the Biblical accounts of creation and the flood. Werner applied Steno's Law of Superposition and proposed five divisions of rock units that is often recognized as the first attempt at a scale of relative geologic time.

• Volcanic or Quaternary was applied to lava fields and other young rocks on top of the Tertiary. Werner felt the heat required to melt rock was from coal burning underground.
• Tertiary or Alluvial referred to unconsolidated sand and gravels
• Secondary or Stratified were solid layered rocks with fossils that originated as mountains that emerged from global oceans (the seashells were now on the mountaintops)
  
• Transition referred to world wide rocks deposited by flood. Werner proposed these rocks generally contain no fossils.
• Primitive rocks were the crystalline rocks representing the first precipitates from the ocean before land emerged

Werner and the Neptunists were opposed by the Plutonists. Anton Moro (1687-1750) published concerning the seashell on the mountain top problem (no, I don't speak or read Italian) and studied volcanic islands. Based on his studies of volcanic islands, he proposed that granites had originated as molten liquids. The chief proponent of Plutonism and Moro's thoughts on the origin of granite was James Hutton (1726-1797) who became known as the Father of Geology. Hutton's Theory of the Earth (and here) was first read before the Royal Society of Edinburgh in 1785, but was considered by many to be essentially unreadable. Hutton felt the core of the Earth was the source of the heat for melting rocks (like lava). He demonstrated that granites were formed, not by precipitation from an ocean, but by crystallization during cooling of melted rock. He did this by tracing granites laterally to where they contacted sedimentary rocks and had baked the sediments like bricks. Hutton argued for uniformitarianism, the idea that the processes that are forming rocks today formed rocks in the past and at essentially the same rates. Hutton also expanded Steno's three principles with the principle of cross-cutting relationships: a rock unit (dike), fault, or fracture that cuts across other rocks must necessarily be younger than the rocks that hosts the feature.

Hutton is also credited with the discovery of “deep time.” While observing the outcropping of rock at Siccar Point, Scotland, he experienced an epiphany that led to the concept of an “unconformity.” The outcrop exhibits a series of layered rocks that are near-vertical and overlain by horizontal rock layers. Hutton realized that the outcrop couldn’t have been formed in a flood. Rather, the upstanding layers had to have been deposited nearly horizontally (Steno), were bent into their upright position, a younger set of horizontal rocks were deposited on top, and finally everything was uplifted from the sea to its present position where Hutton could see it. The surface between the older upstanding rocks and the younger flat rocks must represent a missing period of time not represented by rocks in that outcropping. Geologists now recognize unconformities as a time of erosion or non-deposition.

Hutton, of course, didn't win the origin of granite debate immediately. It wasn't until John Playfair (1748-1819) and Charles Lyell (1797-1875) expounded upon and popularized his ideas that the origin was solved (at least for the time, more later).

For more on rationalism versus empiricism, see the Stanford Encyclopedia of Philosophy. For more on deep time, see Steven Jay Gould's book, Time's Arrow, Time's Cycle.