Stories in rock

Most people notice the different layers, thicknesses, and colors of rocks. They are the ubiquitous backbone of our scenery and when uplifted and eroded into shapes like mountains, arches, mesas, buttes, caves, canyons, and cliffs they become the focal points of parks and scenic overlooks. Other than that, rocks usually don't get much attention except from geologists. Not only do we admire them from afar, we look at them with microscopes, x-rays, and MRI. We crush them, dissolve them, sort them by size, and dye them. We see which parts float in what liquids. The things geologists haven't done to rocks to try and tease out a bit more information probably just haven't been thought of yet.

The rocks that contain fossils are sedimentary rocks. As part of the rock cycle, erosion breaks rocks into particles. These particles are moved around by wind, water, or ice and eventually settle into layers. Each process, blowing wind, still or flowing water, and creeping ice leave traces in the rocks. Wind blown dust is small. The particles are often sharp, angular, and frosted like ground glass. Swiftly flowing water rapidly rounds and polishes particles and sorts them by size. As flowing water slows down, bigger particles settle first followed by smaller ones.

Each environment places its own characteristic mark on rocks. Geologists study many modern environments: beach, estuary, swamp, marsh, reefs, barrier islands, sabkha, tidal channel, river, delta, pond, lake, desert, and more. The conditions that prevail in each environment leave clues in rocks that can be used as analogs to determine how ancient layers were deposited; this is Hutton's "uniformitarianism". The type of rock deposited is often limited by the environment. Most limestones form in relatively shallow, warm tropical seas; they don't indicate arctic conditions. Coal forms in swamps. The rocks on an ocean beach pile up differently than the rocks forming in a delta where a river meets that same ocean.

Fossils also are characteristic of the environments where rocks form. A mixture of fish, shells, and star fish indicate ocean conditions. The tree trunks, branches, and leaves (as in coal) indicate swamps. Some environments don't have many fossils. Creatures that die in open, temperate grass lands are scavenged, scattered, and crushed. Bugs and microbes finish the job breaking down the bones into the soil. In other places, the relentless action of waves grinds any fossils to tiny particles you wouldn't recognize as a fossil, but geologists with a microscope would.

It is the type of rock (limestone, sandstone, shale, and others), the mixture of particle sizes and shapes, the abundance and types of fossils, the marks left by wind, water, and ice (ripples, cross bedding, striae, and more) that all tell stories about how a rock layer came to be. The rock layers are stacked one upon another in somewhat predictable patterns. Rock types formed side-by-side over large distances can often be stacked as well. For example, along the Gulf Coast from New Orleans to Key West several different rock types are being deposited. As these environments shift over time, the places where mud (Mississippi River delta), quartz sand (Destin), and lime sand (Key West) will shift and stack.

The processes responsible for depositing rocks occur at different rates. Floods, storms, landslides, slumps, and earthquakes are all very fast and each can change the rocks being deposited in the course of seconds to weeks. Glaciers, lakes, and rivers are slow, the processes often persisting for thousands of years. Regular daily tides move mud around broad flats (like the Bahamas) but show variations related to spring and neap tides; the deposition of a single layer may be fast (a day), but the environmental conditions may persist for millennia. All of these processes are dynamic, a continuous cycle of eroding and depositing, shifting environments, and drifting continents.

It is the stacking of rock layers that demonstrate the many layers weren't deposited by a single catastrophic flood. The variations of rock layers over time show rocks were deposited by many different processes. In geology, the studies of the environments and processes whereby rocks are deposited and then relating that information to understanding ancient layered rocks are stratigraphy and sedimentology.

Of Fossils and Floods

Fossils are the remains of ancient life preserved in rocks. Fossils may be the hard parts of animals (teeth, skeletons, shells, stems, and the like), impressions (trees, leaves), traces (tracks and trails), and organic chemicals (collagen as in the recent T. Rex study and others). "Fossil" fuels, coal, oil, and natural gas, are the cooked and altered remains of plants and animals.

In the early 1500's, the exact nature of fossils was a topic of much debate. There were several prevailing theories: they were creatures that lived and grew in the rocks; or, they were creatures that had perished in the Biblical flood. Another theory claimed they were marks left in the rock by Satan to vex humanity. Leonardo da Vinci thought a great deal about fossils and between 1506 and 1510 he wrote down his ideas in a manuscript that is now known as the Codex Leicester.¹ Observing that there was a mixture of large and small shells, that they showed growth lines, that there were no nutrients, and the creatures couldn't move around, Leonardo concluded the fossils were once living creatures that had been buried. This left the question of how the fossils came to be on dry land and at the top of mountains.

Leonardo dismissed the notion that fossils originated as a result of a global flood. Leonardo reasoned that if there were a global flood:

1. There would be nowhere for the water to go when it receded.
2. The rocks containing fossils would be a single layer containing a vast and jumbled mixture of shells rather than in the regular steps and layers that characterize the rocks.
3. The torrential rains of a great flood would carry fossils downhill and away from mountaintops and land.

Leonardo described oysters and corals and considered it impossible that a single flood could have carried them 300 miles inland and uphill, nor could they swim or walk there. Leonardo's reasoning was clear and simple. He concluded that fossils were creatures that once lived in the seas and the rocks formed when those seas were somehow lifted up to the mountains. This uplift wasn't adequately until the mid 20th century when Alfred Wegener proposed continental drift which was expanded into the idea of Plate Tectonics.

¹ The Codex Leicester has been scanned, translated, indexed, and produced as a multimedia CD by Corbis. Unfortunately, it is out of print and you may have to look for it at your local library (where I found a copy). Other print editions are also available.

Principles of Geology

Each branch of science is based on fundamental principles. The periodic table in chemistry and conservation of matter and energy in physics are examples. The founding principles of geology are:

1. (Nicholas Steno, 1638-1686) Superposition. In an undisturbed sequence, a rock layer is younger than the layer upon which it rests and older than the rocks that rest on it. Like a brick wall, older rocks (like the first laid bricks) are at the base of a sequence and younger layers (later courses of brick) are on top.
   

2. (Steno) Original horizontality. Sedimentary rocks were originally deposited in nearly flat layers.

3. (Steno) Lateral continuity. Within the limits of a particular environment, similar sequences of rocks from one area can be matched to those in another area: across a valley, extending underground, and even across continents.

4. (James Hutton, 1726-1797) Cross-cutting relations. A fold, fault, or volcanic rock is younger than the rocks it effects.

5. (Hutton) Unconformities. Some boundaries between rock layers represent significant time during which either no rocks were deposited or pre-existing rocks were removed by erosion.

6. (Hutton) Uniformitarianism. The “present is the key to the past” idea. Environments and processes we see shaping the Earth around us today can be used as models for what happened in the past.

7. (William "Strata" Smith, 1769-1839) Faunal succession. The fossils in a rock are unique to that unit. This modern name implies change through time, but succession is a more recent idea than the original concept. Charles Darwin didn't publish Origin of the Species until 20 years after Smith died.

These principles form a set of guidelines for studying rocks. They are not unbreakable laws like the law of gravity, for example. They do, however, establish an orderly way to begin the study of rocks. When a sequence of rocks doesn't conform to these principles, geologists know to look closely and carefully to determine what the story is that the rocks are telling.

Apparent violations of Superposition, like the Lewis Overthrust, for example, are often cited as cause to reject geology and the fossil record. This criticism fails to admit that geologists (and many others): 1) have observed rocks moving in earthquakes; 2) have seen and investigated the structures and marks left in rocks by that movement; and 3) have found those same features in faults and overthrusts that may have moved millions of years ago. Geologists have been able to trace the movement of the rocks over time and match the rocks that moved to their original positions.

Before I leave this subject, a couple of terms should be defined:

1. Fault -- a break in a sequence of rocks along which movement has occurred, the San Andreas Fault for example
2. Fold -- an upward (anticline) or downward (syncline) bending of rocks (occurs after they were formed or deposited)
3. Overthrust -- a type of fault that is nearly flat and where the rocks above the fault have moved a long way relative to the rocks below
   
4. Thrust fault -- a type of fault implying a specific movement of one side of the fault relative to the other

As a geologist, I'm sorely tempted to define such minutiae as hanging wall, foot wall, normal fault, slickensides, recumbent folds, facies, and others, but I hear the patter of patter of dodos approaching.

Faith and Open Minds

Conservative and "fundamentalist" Christians often the criticize the scientific world view for its failure to consider their viewpoint; scientists are closed minded. This critique is incorrect.

Faith is "a belief that does not rest on logical proof or evidence"¹, see Heb 11:1. Faith is thus immune to evidence. No scientific claims made, evidence collected, or logic applied can ever be expected to dissuade someone of their faith-based notions. Faith itself is considered evidence of things not seen. This argument is transparently false; faith that the Sun is a horse-drawn chariot driven across the sky doesn't make it so.

Openminded, on the other hand, is defined as "having or showing a mind receptive to new ideas or arguments".² Science is malleable. As new evidence and ideas are tested and verified, scientists change their minds. Conservative Christians label this provisional nature of science a weakness. It certainly doesn't help that some philosophers question whether an objective reality exists and if anything can be known at all.

In Biblical times, the world's best thinkers knew the Earth was flat and the sky supported by pillars (see for example Job 9:6 and Psalms 75:3). Copernicus, Galileo, Columbus and others demonstrated otherwise. Without their foundation for a spherical earth and a heliocentric solar system, the ability to launch weather, communication, and digital television satellites would be impossible.

Scientists change their mind for good reasons. That doesn't mean they can't fool themselves or be fooled by others. Science, unlike faith, is self-correcting. Self-delusion and fraud will not stand the scrutiny of reasoned testing and evidence.

1. faith. (n.d.). The American Heritage® Dictionary of the English Language, Fourth Edition. Retrieved April 22, 2007, from Dictionary.com website: http://dictionary.reference.com/browse/faith

2. openminded. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved April 22, 2007, from Dictionary.com website: http://dictionary.reference.com/browse/openminded