Secrets in Sedementary Rocks

[This is a follow-up post to the first Geology post from a few weeks ago.] 

These rocks need names.  Each of the big limestone boulders in the circle in our outdoor classroom has something unique to offer the curious eye.  I'm sure by now most students have decided which rock is their favorite to sit on when they visit the outdoor classroom.  For now, I'll number the rocks 1-8, but hopefully students will come up with actual names for them. 

Rocks 1-4, left to right in the picture.

If you follow the main path into the circle, rock number one is on the left.  Then continue counting around the circle.  The fence is between 4 and 5.  Rocks 7 and 8 are the last ones, and they have been placed right next to each other.

Stand in the center of the circle and look around at the rocks.  What are the first things you see?  I see scrape marks, those lighter marks on the rocks where some serious equipment carried them from somewhere else in TN to here.  Next I notice that the rocks look layered.  These rocks are sedimentary rocks, formed over thousands of years as water dropped off layer after layer of tiny mineral particles (more below).

Let's take a look at a few specific rocks in more detail and see what they have to tell us.

Rock #1:
Most of the rock does not contain visible fossils, but there is a gigantic nautiloid fossil that is fairly easy to locate on the surface of the rock.  Hard structures of ancient creatures formed fossils easily, and nautiloids had hard, segmented structures that left fossils like the one to the right of my finger below.  Nautiloids were predators, and where there are predators, we know there has to be prey.  Nautiloids' prey organisms were soft-bodied, so they didn't tend to leave fossils.  The amount of rock that contains a nautiloid is small compared to the rest of the rock because nautiloids were fairly rare in their ecosystem.

Rock # 2:
This rock has a fossil from an organism called a bryozoan.  Bryozoans are filter feeding animals that live in colonies.  They are much like corals, though they are not closely related to corals.  It's common for organisms to be similar and yet unrelated.  For example, penguins and dolphins have many similarities (shape, color, swimming style), yet they are very different types of organisms: penguins are birds and dolphins are mammals.  In the same way, bryozoans and corals are similar in shape and habit yet unrelated.  Bryozoans were much more common when these rocks were formed (300-500 million years ago!) than corals were, and there are several bryozoan fossils on our rocks.

T-shaped Bryozoan fossil on Rock 2.

Rock 3:
Find the crystal-lined hole in Rock 3.  You have found a geode-like structure.  Geodes can form in different ways, but it is likely that this one formed when part of the original sedimentary rock dissolved and washed away to leave a hole, or cavity.  Then over thousands of years, water seeped through the cavity.  Water usually has dissolved minerals in it, and sometimes those dissolved minerals crystallize into solid minerals.  If you have an older faucet at home, look for a whitish crust around it - the white crust is crystallized minerals from the water that is carried through the pipes.  I suppose if the conditions were right your faucet could be covered with pretty crystals in a few thousand years as more and more minerals are deposited on it.  The same process that makes the crust on your faucet made the geode you see in this rock.

A geode-like cavity in Rock 3.

Rock 7:
Rock 7 is my favorite for looking at the layers of sediment that formed the rock.  For some reason, this rock was placed on its side, so the layers are more easily visible.  Flowing water makes sedimentary rocks.  Fast-moving water picks up larger, sand-sized sediment and carries it until the water slows down.  Then the sediment falls out of the water and settles on the ground in a flat layer.  Slower-moving water picks up smaller particles, like the particles that make up mud.  When slow water stops moving, it drops its particles onto the ground.  If the speed of the water above the ground changes through the decades, the sediments that settle onto the ground will have different textures.  The darker, smoother bands in Rock 7 were formed from slow-moving water's particles.  The lighter, rougher bands were formed from faster water's particles.

Layers in this sedimentary limestone reveal the speed of the water that deposited the particles.

There are lots more treasures to find on these rocks, so look carefully.  There are many more fossils, interesting rock layers, geode-like structures and other strange features.  I would like to thank Mr. Smail for teaching me about our rocks.  Feel free to email him if you have more Geology questions!

Looking Over Clover

To any person who has spent enough time sitting on a patch of lawn to get a little bored, the leaf in the picture below will be instantly familiar. 

One clover leaf.

It's a leaf of the white clover plant, and there is plenty of it at out outdoor classroom right now.  One clover leaf has three parts, which is reflected in the Latin name of the plant: Trifolium repens.  Tri- means three, and folium means leaf.  Repens means reclining, which this plant does well, as it spends its entire life within about 3 inches of the ground.  Clover leaves usually have faint white lines in them, and they are never heart-shaped.  Another common lawn plant called oxalis has leaves divided into three heart shapes, and sometimes people get confused about it.

A patch of clover.  See any lucky ones?

White clover has several claims to fame.  First, they are tough little plants, and they survive well on lawns even under heavy foot traffic, so they grow everywhere there is a lawn.  People who are sticklers for uniform-looking lawns consider the plant a weed, but many people value the plant for its ability to grow in harsh conditions where grass can't grow.  Second, clovers are known and loved for their sweet-smelling flowers, which are white or pinkish clusters on stems.  I bet you have made a flower chain from clovers before.  Bees love the flowers even more than humans do, and they make great honey from it.  The sight of clover flowers on a lawn should serve as a warning to wear shoes, since bees are likely to be on the flowers, and stepping on a bee will get you stung.  Clover's third well-known benefit is its value as a food source for animals.  Clover seed is often included in the mix of seeds farmers plant for growing cattle forage (the plants cattle eat).

A small clover plant with leaves, stems and roots.

Clover also has a secret.  Most people don't know much about the hidden power that makes clover so important in nature and explains some of its better-known characteristics.  If you dig up a small clover plant and look at the roots, you see something that is not usually present on plant roots: tiny lumps.  Those lumps are called nodules, and they are actually little areas where clover keeps its own pet bacteria.  The clover provides food and housing (and maybe even affection) to the bacteria in return for the services the bacteria provides to the clover.  The bacteria produce an otherwise almost unobtainable nutrient called nitrogen.  Nitrogen is a nutrient used to make protein - the microscopic parts of organisms that provide much of their actual structure as well as much of the machinery to conduct life's processes.  Other plants can only get nitrogen by absorbing leftover nitrogen from dead clover-type plants or from decomposing animals or animal manure, but clover has its own constant supply.

Root nodules on a clover - where nitrogen is fixed.

Clover's source of nitrogen means it can grow on poor soil where grass can't.  It also means it has a high nitrogen content, making it more nutritious than grass for animals to eat.  When clovers die, they leave behind richer soil with more nitrogen, where other plants can now grow.

Clover is related to bean-type plants (pinto beans, Limas, black beans, lentils, peas), and all types of bean plants have the same pet bacteria for making nitrogen (actually called fixing nitrogen).  This type of interaction between two organisms that live in close contact and help each other is called mutualism.   Can you think of other examples of mutualisms?

Have you ever found a four-leaf clover?  Sometimes the plant makes an error when growing its leaves, resulting in our four-leaf symbol of good luck.  If you look at a patch of clover for long enough, you will probably find a four-leaf clover.  If you do, press it flat between pages of a book for a week or so, then you can glue it to paper or press it between clear tape to preserve it.

Nandina: A Berry Interesting Problem

Oh, nandina, nandina, you trouble my heart!  You are so beautiful all winter with your green foliage and bright red berries, but you are an invasive plant.  What is a good naturalist to do?

Nandina, AKA heavenly bamboo.

Invasive species (species = type of organism) are a problem in Tennessee, and in the rest of the world as well.  They are currently the #2 cause of extinction of other species, just after habitat destruction.   Invasive species are non-native organisms that grow like crazy and take over.  Non-native organisms are moved from one part of the world to another, mostly by humans.  This is usually not a problem, except that for some non-native species, the new habitat has none of their usual diseases and predators, and the habitat seems to fit just right.  In that case....they can take over and crowd out the habitat of other organisms.  Nandina is native in Asia - from Japan west to India.  It is a beloved plant there, also used in landscaping like we use it here. 

Poisonous beauty: these berries contain nandina seeds and cyanide!

In Tennessee, some of our most harmful invasives are bush honeysuckle and kudzu.  Bush honeysuckle uses up habitat for other plants.  Also, birds that nest in it are more likely to get eaten (not sure why).  Kudzu simply crowds out every living organism where it grows.  Nandina is not that bad!  It is usually only found growing wild near where humans have intentionally planted it.  The Tennessee organization that helps keep invasive plants under control (TN-EPPC)  wants more information about nandina in order to keep tabs on the problem.  If you are ever out hiking in the wild (not in a landscaped yard) and you see a nandina, TN-EPPC would like to know about it.  You can report an escaped nandina at the TN-EPPC website: http://www.tneppc.org/

A nandina draws your gaze from behind a sedimentary rock.

Biologists worry about invasive species because they cause the total number of species to decrease.  The loss of a species, or extinction, causes the loss of a participant in an ecosystem.  For example, when a bird species dies out, an ecosystem might lose a seed-disperser.  If honeybees died out, there would be way fewer pollinators and thus way fewer fruits and seeds.  If a type of beetle died out, we might lose a soil recycler. 

Nandina is guilty of taking up a tiny bit habitat that would otherwise be used by native species, though it doesn't appear extremely aggressive.  It has another problem, though.  Nandina berries contain a toxin called cyanide.  Birds in the US haven't figured out how to deal with the poison, and some cedar waxwing birds have died from eating lots of the berries.  The berries can be toxic to any other animal too, so don't eat them. (It probably takes a lot of berries to hurt a large animal such as a human...still...don't eat them.)

Back to the original question: what's a good naturalist to do?  That depends on who you ask.  Some will say to never plant nandinas.  Others say plant them but clip off the berries this time of year when birds start foraging.  Others say don't worry about it - eventually the other species will adapt and nandina will become another important part of our ecosystem.  The only problem with this last option is that adaptation takes hundreds to thousands of years, so we won't find out how nandinas mesh with our Middle Tenneessee ecosystem for a looooonnnngggg time!  What do you think we should do?