9.1 How do we infer the relative ages of events?
Principle 1: Most sediment is deposited in horizontal layers.
Principle 2: A younger sedimentary or volcanic unit is deposited on top of older units.
Principle 3: A younger sediment or rock can contain pieces of an older rock.
Principle 4: A younger rock or feature can cut across any older rock or feature.
Principle 5: Younger rocks and features can cause change along their contacts with older rocks.
9.2 How do we study ages of landscape?
1. Sequence begins with new sediment on top of igneous rocks. 2. Through time, environment changes and a series of different sedimentary layers form on top. (Younger layer on top) 3. Over time, deposition stops, weathering and erosion can begin. 4. Uplifted/seas withdraw; the area can begin to be eroded by elements. ( Rivers, streams, glaciers, and wind) 5. Tributaries, sculpts a deeper, wider and more intricate canyon.
9.3 What is the significance of an unconformity?
Angular Unconformity 1. Gray limestone is deposited under the sea in horizontal layer. 2. The sea withdraws and the limestone beds are folded. 3. A conglomerate is deposited over the eroded beds.
Nonconformity
1. Begins when granite is uplifted to the surface, and then is weathered into a reddish zone of sand, clay and iron oxides. 2. Weathering of granite, the sediment citifies to produce sandstone and conglomerate.
Disconformity
1. Any type of sediment rock is deposited of horizontal layer. 2. Rock is exposed at surface because its uplifted, weathering and erosion affect the land surface. (sediments stop) 3. Over time, sedimentation resumes and the surface of older rocks is buried by a younger layer of sediment.
9.4 How are ages assigned to rocks and events?
Before any decay After one half-life After two half-lifeAtoms of Parent 100 50 25Atoms of daughters 0 50 75 |
Mass spectrometer measures the ratio of parent isotopes to daughter product in the rock the mineral to be dated.
9.5 What are fossils?
1. Can be preserved in a rock or sediment, differs, depending on what type of life is involved. 2. Encounter footprints called Track way, where geologist can examine how they moved, weight, and whether it traveled alone or in groups. 3. Encounter worms and other creatures dig, or tunnel into mud, forming cavities that can be filled by a different sediment. Worm burrow. 4. Hard parts: preserved as a fossil if it has a shell, bones, teeth, or some other hard parts. 5. Rapid burial: cannot be preserved if on surface, exposure to the atmosphere and water. 6. Dendrites and Concretions.
Dendrites grow in branching patterns along joints and between sedimentary layers.
Concretions grow in sediment during cementation.
9.6 How and why did living change through geologic time?
1. The Cenozoic era, recent life, spans the last 65 million years. Called the age of mammals. 2. The Mesozoic era, known as the age of dinosaurs. (251 MYA) 3. The Paleozoic era, dominated by several major groups of marine animals. Extinct of the great dying. 4. The Precambrian, comprises nearly 90% of geologic time. Only simple life existed, such as bacteria and algae. 1. Environment setting-animals, plants and other organism have certain ways they live. 2. Climate-(change), resulting in loss of water and food sources. Can eliminate entire classes of animals. 3. Reproductive strategy, different plants and animals reproduce in different ways. Some reproductive strategies will be more successful than others. 4. Adaptability, the more adaptable a species is, the more likely it will survive changes in the environment. 5. Competition, two or more species compete for the same sparse resources. 6. Predators and prey, being food
