Geology begets biology. North facing vs. South facing slopes

I taught High School biology for a long time, almost my whole K-12 career. Of course, that meant my biology classes had a decidedly geological slant to them. One concept I tried to instill in my biology students was that the literal underpinnings of the ecosystem was the underlying geology.

I called these explorations "Geology begets Biology"

One idea that seems simple but created problems with many students was north facing slopes vs. south facing slopes. Both sides of a hill receive approximately the same amount of precipitation, have similar soils and experience the same temperatures but can appear very different from each other. However, the south facing slopes receive more direct sunlight and snow will melt faster, soil moisture will evaporate faster creating a dryer micro climate than the shady north facing slope which might be only meters away. The slower evaporation on the north side means that plants (that biology connection) will have more available moisture. With the snow melting at a slower rate, there is more water available longer in to the spring.

Ultimately, the species of plants found on south facing slopes will be more drought tolerant while their north facing cousins less skilled at surviving with low water amounts. Here, in Colorado's southern mountains, the north facing slopes are full of large evergreen trees, while the south side has more shrubs like the ubiquitous sage brush. So, in just a glance we should be able to roughly decide on "north" even without a compass.

In the foreground, the grassy slope is facing south and west while the heavily treed area is more north and east.

Notice the scrub oak. What you can't experience is the snow depth under the oak is only a few inches.
Looking across the gully at the fully melted south facing slope. I was traveling on the north facing slope in 8-10 inches of snow from a recent storm while the other side is clear.
Again, looking across the gully at the melted out slope. I was in the shade of a large Ponderosa pine tree. The south facing side is home to a large population of scrub oak trees

A visit to our Grandson and the Pacific Plate

We spent the MLK weekend visiting our almost one year old grandson (and family) in California. One day, we traveled across the Santa Cruz mountains to the ocean and visited a small state park, Natural Bridges State Beach with its namesake natural bridge sitting just a little bit off shore. I will admit, I was too busy making faces and goofy sounds and generally playing grandfather with the baby to notice when we crossed over from the North American Plate to the Pacific Plate. I guess I will pay more attention on the next visit.

Once at the state park we spent some time exploring the beach. Having spent most of my geology career in Colorado and Utah, I find visiting a current beach to be lots of fun. The beaches I usually frequent were sea side back in the Permian.
The rock was a fun mudstone. A very fine grained sedimentary rock, Miocene in age. Again, I am used to pretty soft sedimentary rock in the canyons of Utah. This mudstone was, pardon the expression, rock hard! The cementing agent of SiO2 has created a very erosion resistant rock that made some great tide pools, ocean side cliffs and
... of course the natural bridges. In the recent (historical) past there were three bridges present. Two have succumbed to the power of erosion leaving the sole remaining bridge, for now. Reading a web site from the University at Santa Cruz the author suggests that the bridges have been transformed from a natural wonder into an educational resource.As for being on the Pacific plate. It didn't feel very different, but I thought I could just faintly detect a little more northward motion instead of the constant westward traveling I have been doing my whole life.

The earth will survive

I had the chance to visit an upper elementary classroom just a few days ago. While there I shared how the earth's climate has changed over time. I led them through the idea that we have all kinds of clues about past climate by looking at rocks. So, we examined hand samples of sandstone, shale and limestone and compared the clues from each rock type. We discussed how differences in temperature, atmosphere, proximity to water can change how a rock looks (not bad for a group of kids with no chemistry in their academic history) And if the weather cooperated we would have taken a field trip to some nearby cliffs to see the story they tell.

One student, obviously getting information from her parents, decided to trap me about climate change. She was pretty smug when I replied that yes, the planet itself has survived past changes and will survive any future climate change except perhaps resulting from a large impact or our sun growing into a Red Giant.

Her face fell though when I said, we weren't concerned about the planet as much as we were concerned with the animals and even the human beings on the planet. I am amazed that we must still argue over the presence of climate change here on earth. I guess I'll just keep taking my show on the road one classroom at a time.

I bet the dinner discussion that night was interesting.