Fossils, Geologic , Absolute & , and Natural Resources

Chapters 5 & 6 How Do Form?

 Fossils are found in sedimentary rocks like sandstone, limestone, and shale  In , most fossils are marine in origin. Our state , Chesapecten jeffersonius, is a large extinct species of that dates to approximately 4.5 million ago. It was the first fossil ever described in and is named after Thomas Jefferson, one of our founding fathers, and an amateur paleontologist.  Special conditions need to exist for a fossil to form: 1. Must be protected from scavengers 2. Must be protected from bacteria or micro- organisms that can speed up the decay process 3. Must have hard parts like teeth or bones 4. Be near water so they can be buried fast Can You Name That Fossil? 1 4

Cast Petrified

2 5

Carbonaceous Mold

3 6 Trace Amber and/or Mold

 All events in Earth’s geologic are recorded on the geologic time scale  Divisions of geologic time are eons, , periods, and epochs  Fossils from each major (Paleozoic, Mesozoic, Cenozoic) are found in the rocks of Virginia.  The end of each era is typically marked by a major event.  We are currently in the Cenozoic Era, the Quaternary Period, and the Recent .  By using relative and methods, we have been able to roughly estimate the age of the Earth to be about 4.6 billion years. Virginia Fossils  Paleozoic fossils: , , , and sedimentary rocks crop out in the and Ridge and Appalachian Plateau provinces and preserve abundant marine fossils, indicating the presence of extensive, shallow seas. By the (i.e., 350 million years ago), the western part of the state was covered in lush, dense forests of “scale trees” (lycophytes), horsetails, and ferns. The accumulation of organic material in these large coastal swamps eventually produced Virginia’s coal seams.  Mesozoic fossils: In the Piedmont province, fossils of dinosaur footprints, freshwater fish, and insects are found in rift basin deposits of the . In the eastern part of the state, where the sea had not yet retreated, fossil oysters and belemnites have been recovered from a few outcrops.  Cenozoic fossils: Dramatic changes in sea level occurred throughout the Cenozoic. The rise and fall of sea level is recorded in the richly fossiliferous rocks of Virginia’s Coastal Plain. Amazing numbers of fossil clams, snails, and sand dollars can be found in these marine rocks, along with fossilized whale bones and shark teeth. Mastodon and mammoth fossils, while not common, can be found in Quaternary that were deposited along rivers and lakes. Relative Dating

 Placing events in the order in which they occurred.  The states that the oldest rocks are on the bottom of a sequence.  The Law of Horizontality states that all layers are originally deposited horizontally. Then, they may be disturbed by faulting, folding, tilting, , or intrusions.  The Law of Cross-Cutting states that the intrusion is always younger than the surrounding rock. Number of Fraction Percentage half-lives remaining remaining Absolute Dating elapsed 1 0 /1 100 1 1 /2 50 1  Placing a numerical age on an 2 /4 25 3 1/ 12.5 event. 8 1 4 /16 6.25 5 1/ 3.125  Radioactive isotopes are used 32 1 6 /64 1.563 1 to determine the ages of rocks 7 /128 0.781 and fossils...... 1 n n n /2 100/(2 )  Radioactive isotopes (the parent) decay, or change, at a regular rate into elements that are stable (the daughter).  The rate of decay of the parent is called its half-life. This is the time it takes for half of the parent to change into the daughter.  Common radioactive isotopes are -14, Uranium-238, Strontium-90, and Potassium-40

Natural Resources

 Renewable resources are those that when used up, are replenished in a reasonable amount of time  Examples of renewable resources are sunlight, water, and wood  Nonrenewable resources are the fossil fuels that, when used, take millions of years to be replenished  Fossil fuels consist of coal, petroleum, and natural gas Virginia Resources

 Coal for energy  and crushed stone for construction  Silica for electronics  Zirconium and titanium for advanced metallurgy (The scientific study and technology of extracting metals from ores, refining them for use, and creating alloys and useful objects from them)  Limestone for making concrete