Terrain rating due to >.5 mile walk to cache area, then rough
boulders to climb around on in the vicinity of the cache. Watch
your step.
ROCK
Rock is a naturally occurring, solid mixture of minerals and
organic matter. There are three types of rock. Sedimentary
rock forms when the weight of sediments press down on layers of
sediment, cementing them together. So when rocks of any kind are
weathered -- or broken down into little pieces to become small bits
of sediment -- they have the potential of being recycled and remade
back into rock (sedimentary rock) again!
The other two types of rock are igneous rock-- which is
formed out of the cooling of lava -- and metamorphic rock.
Metamorphic rock forms when heat and temperature change the
texture and mineral content of other types of rock. These rocks can
be weathered and broken down too, and in time that sediment can be
cemented into sedimentary rock.
FOSSILS
When organisms die, they usually decay quickly. If they are covered
by sediment or soil right away, their bones or shells may be
protected from decaying. Over a long time, that sediment gets
pressed down and cementented together, making a sedimentary
rock. The trapped bones or shells become part of the rock! This
is called fossilization and it usually happens in
sedimentary rock.
ROCK LAYERS AND GEOLOGIC TIME
Over tens of thousands and even millions of years, all those rocks
end up in layers under our feet and of course under our oceans. If
we could look at a cross section of the rocks underneath us, we'd
see all those layers! The ones closer to us are younger. The ones
way down deep are ancient! That is, if there hasn't been any
faulting or folding -- shifting around -- of the original layers.
This logical rule about the youngest rocks being above the older
rocks in undistrubed rock layers is called the law of
superposition. We use this law to figure out the order of
events in Earth's history. Determining the age of objects and rocks
this way is called relative dating.
THE FOSSIL RECORD
Relative dating can also be used with fossils we find, the
fossil record. You can see thousands of fossils right here
under your feet! Fossils of plants and animals show how they
changed and evolved throughout Earth's history. An organism that
changes a lot, that develops visible adaptations as it evolves,
helps us in figuring out geologic time too. For example, a fish
that lived 50 million years ago may look a lot different than its
ancestor that lived 200 million years ago. When we find a fossil of
the older fish, we know the rock around it is 200 million years
old. If the fish didn't change at all over time, we wouldn't be
able to tell the younger rocks with that fossil from the older
rocks with the same type of animal.
TO LOG THIS CACHE
1. First, find the largest fossilized shell you can, at or within a
few feet of ground zero. It is shaped like the logo for Shell gas
stations, and it was a scallop when it lived. You can find the same
type of shells on the beaches that are just a mile away. They look
exactly alike! Not much evolution going on there.
Would this be a good fossil to use to try to figure out how old
this limestone is? ____ Why or why not?
2. Do you find any plant or animal fossils here? I only see
fossils of shell and coral. Find the closest coral fossil to GZ.
There is a picture of it in the Gallery of this listing. Living
here in Florida, we know that corals thrive in warm saltwater.
What can you infer about the environment in which this fossil
probably formed?