Soil, Rocks, Fossils, & Geologic Time

1. Soil, Rocks, Fossils, & Geologic Time

2. Soil: a mixture of weathered rock, decomposed organic matter (humus), water & gases • Layers: Horizon A – Topsoil – rich humus layer one foot or less Horizon B – Subsoil – clay & minerals washed down from above Horizon C – Regolith – transition layer of partly weathered rock Bedrock • Soil Conservation (conservation is using natural resources wisely) • Can take more than 100 years to create 1 inch of topsoil

3. Rock Cycle: the process where rocks are formed, destroyed, and formed again in Earth’s crust • Igneous Rock : formed by cooled molten material (grainy or glassy). • Metamorphic Rock: formed by changing existing rock through heat and pressure • Sedimentary Rock: formed through deposition of sediment called lithification (thin layers). • Lithification: the process of turning sediment into sedimentary rock: Weathering → Erosion → Deposition → Compaction → Cementation → Sedimentary Rock

4. Pluton: an intrusive igneous rock body • Sill forms when magma intrudes parallel rock layers • Dike forms when magma invades vertical cracks in rock layers, cutting across preexisting rocks • Batholith is a large, irregular shaped pluton of at least 100 km2 (stock if less than 100 km2) • Laccolith is a lens shaped pluton with a round top and flat bottom. It is relatively small, no more than 16 km wide.

5. Weathering → Erosion → Deposition Cycle Weathering: the process that breaks rock into smaller pieces • physical/mechanical : Breaking rocks into smaller pieces that does not involve any change in the composition of the rock, only changes in size or shape occur. examples: Wind, water, abrasion, temperature, plant roots, & animal actions. • Frost wedging occurs because water expands when it freezes.

6. Chemical weathering: the process by which rocks and minerals undergo changes in their composition due to water & acids from nature (plants, fungi, gases in the air, etc.) • Erosion: the process of carrying weathered rocks away • Agents of erosion: wind, water, ice, & gravity

7. Mass Movement. • Slump: when the mass of material in a landslide moves in large mass, leaving crescent shape scars • Slide: a rapid, down slope movement of Earth materials that occurs when a sudden separation from underlying materials • Creep: a slow, steady, downhill flow of loose, weathered Earth materials (as little as a few cm/year) • Flow: Earth materials flow as if they were a thick liquid (a few cm/year up to 100’s km/hr) • Fall: when a rock loosened by weathering, breaks off and falls directly downward off a cliff or overhang. • Increases in water increases total weight and lubricates grains between sediment reducing friction between particles contributing to mass movements.

8. Relative Dating • Law of Superposition: the geologic principal that states that in horizontal layers of sedimentary rock, each layer is older than the one above it, and younger than the one below it. • Intrusions and Extrusions are used in relative dating of rock layers. • Extrusion: igneous rock that is younger than rock below it • Intrusion: igneous rock that is younger than rock below it or around it • Law of Cross-Cutting Relationships: any fault or intrusion is younger than the layer it cuts through. • Law of Included Fragments: any fossils or rock fragments found in layers were deposited at the time the layer formed .

9. Fossils • A fossil is the the preserved remains or impression of a prehistoric organism • A scientist who studies fossils to learn about organisms that lived long ago is a Paleontologist . • Types of fossils: 1. Preserved Remains – unchanged, or nearly unchanged remains preserved in tar, amber, or ice protecting it from decay 2. Petrified – minerals replace all or part of an organism

10. Carbon Film – a thin coating of carbon left on rock by organic gases of decomposition. 4. Molds & Casts – a hollow place in the sediment forms from the dead organism, the mold is later filled in with new sediment to form a cast. 5. Trace Fossils – show evidence of organism activities • To be classified as an index fossil that is used to tell the age of a rock layer, the fossil must be found in many areas and the organism must have existed for only a short geologic time frame.

11. Radiometric Dating: using radioactive decay to give an exact age to a fossil or rock • Half-Life: used in dating of radioactive substances. Every half-life the radioactive substance decays into another substance. Example: C-14 has a half-life of 5730 years in which half of it decays into N-14. If a fossil contains 50% C-14 & 50% N-14 it is 5730 years old; if it’s 25% C-14 & 75% N-14 it is 11,460 years old. • Other examples: P-40 to A-40 in 1.25 billion years • U-235 to Pb-207 in 704million years

12. Geologic Time Scale: • Precambrian Era covers 88% of Earth History • Paleozoic Era covers 7% of Earth History - 3 major events in life development during the Paleozoic: 1. Life Explodes in the water 2. Life reaches land – amphibians & plants 3. ended with a mass extinction – 95+% • Mesozoic Era covers 4% of Earth History - the major groups of organisms that developed were: Reptiles (dinosaur), Birds, & Mammals - At the end of the Mesozoic Era, approximately 50% of all life on Earth became extinct • Cenozoic (current) Era covers 1% of Earth History. several ice ages have occurred. The dominant animal life is the mammal.

13. Past Environmental evidence found in rock layers • Ripple marks found in sandstone in a desert tell you that the climate/environment used to be a shallow sea. • Limestone in KY tells us that KY use to be under a shallow sea. • Tropical plant fossils in cold climate (Alaska) tell us at one time its climate use to be warm, moist, tropical. • Glacier tracks in warm areas (Ohio) tell us at one time it’s climate used to be cold & under glacial ice.