<p>Earth Science Chapter 10 – Geologic Time</p><p>Fossil – _____  Most form when living things die and are buried by sediments. Usually found in sedimentary rock.  Must be covered quickly to avoid decay and predators so it can leave an impression  No heat or extreme pressure (not found in metamorphic or igneous rocks)  If just bones, then less can be seen about the organism  Must have hard parts</p><p>Types 1. molds and casts  Mold – _____, forms when _____  Water carrying minerals and sediment seep into empty space of a mold once organic material is gone  Cast – _____ 2. petrified fossils – _____ 3. carbon films – _____  When sediment buries an organism some of the materials that make up the organism evaporate, leaving carbon behind. 4. trace fossils – _____ 5. preserved remains – _____</p><p>Past environments – fossils show evidence of past environments.  Cold or warm weather  Seas or land or swamp  Show evidence of life forms that once existed and _____.</p><p>Absolute age – _____. Relative age of rocks – _____  Law of Superposition – _____.  Uniformitarianism – _____.  Extrusion – _____  Intrusion – _____  Faults – _____. Fault is always _____ than the rock it cuts through  Unconformity – _____ (due to erosion sometimes)  Index fossil – _____. Know a range for the rock age in which the fossil is found</p><p>Atoms – tiny particles make up all matter Element – all atoms of same structure are the same element. Some elements are not stable. Radioactive decay – _____.  They form _____.  Elements break down in predictable ways  Half-life – _____. The time it takes for _____.</p><p>Determining absolute ages  Choose the correct radioactive element for the estimate of the age of the rock.  Potassium-argon dating. _____ years half-life and used in most ancient rocks  C-14 dating. _____year half-life. All life contains C and some C14. Used for life forms from _____years ago  Rock layers – does not work on _____ rocks because they contain pieces of other rocks. However, it works well with _____ rocks so scientists use intrusions and extrusions to get an approximate/relative age.</p><p>Geologic time scale is a record of the life forms and geologic events in Earth’s history.  Precambrian Time – _____% of earth’s history ended _____years ago (mya).  After Precambrian time the scale is broken into _____.  Era – 3, _____.  Periods – divisions of Eras. Periods are split into Epochs.  Divisions are based on _____.</p><p>Early Earth  Earth formed at the same time as the other planets and sun, about 4.6 billion years ago.  Found age using radioactive dating  Moon formed when _____ (moon rocks are about 4.6 billion years old)  Earth began as a _____  Believe that the Earth was very hot due to collisions and melted, denser material sinking into the center forming the Earth’s interior layers  Due to contact with space the outside lost heat and the _____ formed  Earth’s gravity captured gasses to form the 1st atmosphere of H and He. 1. atmosphere – 2nd atmosphere formed by _____ 2. oceans – earth was so hot that all water evaporated. As it cooled it _____ 3. continents – higher parts where water didn’t cover. Remember plate tectonics, the lighter plates float higher – continental plates 4. life – _____years ago 1st single-celled organisms formed. _____years ago photosynthesis began and put oxygen in the atmosphere. </p>