Developing Geologic Thought

By Mary Stroh-Twichell

Geologist & Madrone Circle Donor

Lichen on chert. Photo Courtesy of Summer Swallow

I once wrote: “Scientific knowledge can lead to adaptations, and these are best accomplished by first fostering a receptive attitude not only for scientific data, but for an emotional awareness of the natural world. Only then can there be a base for understanding the ramifications of our actions, and to act towards environmental justice.” Let me break this down.

Take the word “science”, which is being bandied about and even attacked these days. It is from the Latin “scientia” meaning knowledge. A simple definition, then, would be that science is the search for knowledge. Emotional awareness implies that observations are made and thought is given to those observations. Nothing else is as important to the natural sciences as observation and thought about what was observed.

The natural world is the Earth itself and it’s history. Earth has a long history, in the vicinity of five thousand million years, aka five billion. Land masses, oceans, and atmospheres have changed multiple times, so thinking about and imagining processes that have sculpted the Earth over time is a daunting but necessary task to understanding life on Earth. Here is where the geological sciences shine. The emphasis is on geological processes OVER TIME and how they influenced life OVER TIME. These processes have been and continue to be at the base of life on Earth. But, what if I am not a geologist or interested in rocks?

Photo Courtesy of Summer Swallow

It does not take a geology degree to think geologic thoughts. What are some of the geological words you already know, such as faults, landslides, outcrops, sediment, rock, etc.? Now give those words more meaning, and think about WHAT they each are, WHERE they occur, WHEN they took or take place, and HOW they came to be. Use your imagination and then a dictionary (or google!). This is a way to build upon geologic thought without a whole lot of effort.

Believe it or not, geologic thought is necessary to understanding biodiversity. The word geodiversity has not been given the prominence of biodiversity. This is probably because when we hear the word “biodiversity,” we immediately think of all the different plants and animals we see around us every day. We don’t usually think about the ground under our house, or what’s under that hill over there, or how that cliff got there.

Geodiversity has basic definitions such as the range of geological, geomorphological, and soil features or, more simply, the variety of Earth materials and processes that constitute the Earth. Pepperwood, at 3,200 acres, has plenty of examples of how to apply geologic thought and the concept of geodiversity. Consider the lay of the land: the topography and relief. There are hills and valleys, drainages of various sizes and lengths, gentle and steep slopes.

Hills are underlain by more resistant bedrock, a term that applies to any solid rock underlying soil, gravel, or other superficial material. Valleys are low-lying land bounded by higher ground. Drainages are the ways in which water leaves an area, either by surface flow or in subsurface conduits. Slopes have soils, which are the unconsolidated material above the bedrock. Geologists call this material regolith, from the Greek rhegos “blanket”, and lithos “stone.” The look of the land is geodiversity on display.

Let’s dig into some more geodiversity thinking. The following are a few examples.

There is a reddish-brown colored slope with sparse chaparral plant cover south of the Dwight Center, and visible from the reserve road. This is an area of serpentine soils. What does this mean? Geologically speaking, serpentine is a group of rock-forming minerals having high concentrations of magnesium and iron, and serpentinite is a metamorphic rock consisting almost entirely of serpentine-group minerals. Serpentinite has a complex beginning. Serpentine minerals form by hydrothermal alteration as oceanic crust is subducted at a tectonic plate boundary. This descending crust is heated, moving through the upper mantle where magnesium- and iron-rich minerals are hydrated to form serpentine minerals and then serpentinite.

The Leopard Lily (Lilium pardalinum), or Tsawaya Kelshi in Wappo, grows in wet mountain meadows, often on serpentine soils, and benefits from diffuse sunlight. An endangered plant, it grows from small, usually clustered bulbs, and typically blooms in July. Photo Courtesy of Summer Swallow

Faults at plate boundaries provide avenues for serpentinite to surface. It is thought that being less dense than surrounding rock, serpentinite can float to the surface. Or, being greasy and plastic, serpentinite may be squeezed upward, like toothpaste out of its tube. These plate processes happened millions of years ago and in a distant place. It took millions more years for other plate tectonic actions to bring this serpentinite to its location, and for it to weather to form the reddish-brown soils that host life as we see it.

What about the hills of Pepperwood? What is some of their bedrock? If the rock is graywacke, that would mean that the rock formed in an ocean, usually from deposits by turbidity currents. Turbidity currents are underwater debris flows that occur in submarine canyons. Graywacke is a sedimentary rock of variable composition: rock fragments, minerals, and mineral fragments held together by a clayey (dark) matrix, hence the nickname “dirty sandstone.” Graywackes of old age, and Pepperwood’s would be millions of years old, are often metamorphosed making them more resistant to weathering and erosion. Soils developed from graywacke bedrock host a diversity of life as we see it.

Geological processes such as faulting and landslides are part of geodiversity. Faults may interrupt bedrock continuity. They may juxtapose different rock formations, and interrupt or divert water movement. Pepperwood is transected by the Mayacama Fault Zone, a major northwest/southeast trending feature whose influence on the geology is bound to be extensive. Landslides change a slope, the soil structure, and water storage. Both these processes may have lasting affects on biodiversity well into the future.

At Pepperwood, the geodiversity amplifies the biodiversity. Geodiversity is especially important for any discussions dealing with habitat connectivity and corridor issues in a changing climate. For instance, hypotheses and data collection should consider geodiversity as it affects the local hydrologic cycle and water storage, because water is a necessity for most life.

Finally, environmental justice should be considered for all life. We are all in this together. The ability to live in a healthy environment should be a right for all life on Earth. Further, a grounding in geologic thought brings the very long natural history of the Earth into perspective. It can inspire wonder, imagination, and awe and, hopefully, a sense of caring about all life on Earth.

Photo Courtesy of Summer Swallow

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