Layers of Time EarthCache
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The rocks that form this layered mountain are sedimentary. "Sedimentary" means that particles, like soil or sand, or minerals, have dropped or crystallized out of the water. These sediments then built up in layers and turned to rock over a long period of time. Here you find them in nearly in horizontal layers. You can see this layering exposed along the bluffs and natural outcrops and most clearly in highway roadcuts. This layering shows that these rocks began as layers, or beds, of mud on the floor of the stream. These sedimentary beds vary from inches to several feet in thickness. The different beds, and the lines called bedding planes that separate them, record changing conditions while sand and mud were being deposited on the floor. By studying this layering, geologists learn volumes about the ancient environments in which the sediments were deposited. If you observe the layering in the mud at the bottom of a puddle or a stream, it seems obvious that the layers on the bottom of the pile were there before the ones on top and are therefore older. This simple observation has given geologists a means of telling relative time in the history of the development of the rock layers. Those layers on the bottom are older than those on top. Therefore, this pile of layered rocks becomes a record of time - a history of the events that occurred during the formation of the rocks.
The layering you see in a roadcut is just a small part of the overall picture. Geologists have grouped these layers into major units called "formations", which can be hundreds of feet thick. These formations can be traced or correlated across wide areas over hundreds of miles.
TO LOG THIS EARTH CACHE EMAIL THE GC# ALONG WITH THE ANSWERS TO THE QUESTIONS BELOW:
1. How tall do you think this mountain is from top to bottom?
2. How do the layers of rock feel at the base of the mountain? Compare it to something you find in your home.
3. How do you think the layers towards the middle of the mountain feel?
4. Which layers of the mountain are older?
RESOURCES:
1. Wikipedia: Sedimentary Rock
2. Wikipedia: Mountain
Additional Hints
(Decrypt)
Hfr gur ynetr cnexvat gheabhg gb cnex naq hfr gur jryy sbezrq genvyf gb TM, orpnershyy naq unir sha. :)