Earth History

Earth history Vocab Sedimentary rock layers - formed by the accumulation of sediments (sand, silt, clay) Rock layers provide a history of how life forms have changed over time

Earth history vocab What is a fossil? Fossils – evidence of former life on earth What conditions do they form under? Low oxygen levels, fast burial, low heat Provide proof of how life and environmental conditions have changed

Earth history vocab Lithospheric plates regions of Earth's crust that are divided into plates that move across the surface of the earth

SAMPLE LIFE TIMELINE 1988 – Birth, at the hospital 1991 – little sister is born 1993 – started school (kindergarten) 1999 – my cousin came to live with us 2001 – my cousin moved out 2002 – graduated from 8th grade

Interrupting fossil layering Folding of rock layers due to compression Uplift occurs when areas of the crust move up due to tectonic plate movements Folding video if time

Index Fossils Used to define periods of geologic time Should be… distinctive, widespread, abundant Limited in geologic time

Relative Dating Uses rock layers and fossils to determine age of rocks Example: Law of Superposition - undisturbed sedimentary rock layers are in age order A and B activity

How to use relative dating Fauna A 1 Rapidly spread 2 Dies out quickly 3 Valuable Index Fossil Fauna B 1 Spreads slowly 2 Does not die out quickly 3Poor Index Fossil

Relative dating practice

Absolute dating Allows scientists to date a rock to a specific year or range of years Example : Carbon 14 (radiocarbon) dating Uses the amount of C 14 in a dead organism to estimate how old it is

Is rock layer "A" younger or older than the other rocks Is rock layer "A" younger or older than the other rocks? What evidence explains your answer? Is the fault (dotted line labeled "L") older or younger than layer D? Explain your answer. List the rock layers in order from oldest to youngest. (include the lines "K and L"). E, f, g, h, I, j, l, k, d, c, b, a

Radioactive dating Is a form of absolute dating Calculating age by measuring the amount of radioactive material a substance contains Radioactive material – unstable elements that break down over time Ex : Uranium

Uranium Is radioactive Cannot be altered by temperature or pressure The rate at which it breaks down (decays) is constant Cannot be altered by temperature or pressure Using uranium, scientists have dated the earth to be 4-5 billion years old

Radioactive Dating Practice If 100 grams of pure carbon-14 starts to decay, how many grams of carbon-14 (N-14) will be left after 11,400 years?

Rock Cycle 3 main types of rock All rocks on earth were once igneous rocks Igneous rocks - form as liquid magma cools Intrusive igneous- cooled below the surface Extrusive igneous- cooled on the surface Extrusive igneous rock

Rock Cycle Sedimentary rocks – form from deposits of sediment on the earth’s surface ( usually in aquatic environments) Metamorphic rocks - form deep in the Earth when heat and pressure are applied to igneous or sedimentary rocks http://www.learner.org/interactives/rockcycle/diagram.html

Rock Cycle Questions How was it formed/made? Was it “birthed” in hot or cold conditions? Would you expect it to have layers? Are you likely to find fossils in it? Why? What can it turn into next? Memory trick / picture http://www.learner.org/interactives/rockcycle/diagram.html Question Number Igneous Metamorphic Sedimentary 1 From cooling magma either inside or above the earth From heat and pressure applied to sed or igneous rock 2

Identifying rock layers How can we identify a rock layer? By minerals – color, hardness, metallic or not By temperature – affects size of crystals By how much pressure made it - density of rocks

Rock id challenge Contains numerous bubble-like cavities that may or may not be lined with minerals, Has obvious bubbly or frothy texture, Is fine-grained, uniform in texture, glassy, Made of discrete mineral grains locked together (may be loosened by weathering) Has obvious stratification, Very soft (easily scratched by a knife), Obviously made of particles cemented together, Contains fossils Has a fine texture with an obvious directional grain (foliation) Has obvious bands, streaks or clumps of different minerals Is made mostly of quartz or calcite but is coarse-grained and lacks sedimentary features, May often have features of original rock but is recrystallized or chemically changed

ICE CORE VIDEO QUESTIONS Ice cores provide a high resolution record of hemispheric and ___________ scale climate change. The ice is taken from the _______ of the core so it is not contaminated. Ice cores tell us about the ancient _______________ of Antarctica.

A storm with high winds moves over a large lake A storm with high winds moves over a large lake. What effect does this have on the lake’s water quality? A It decreases the turbidity of the water. B It increases dissolved oxygen levels. C It decreases the acidity of the water. D It increases the pH of the water.

Which energy resource does not ultimately rely on the Sun? A solar cells B biomass C wind D geothermal