1. Earth’s History The Rock Record

2. Topic 1 – Telling Time Kinds of Time –2 types 1. Relative time – places an event in order by comparing it with other events –Example: Sedimentary Rock layers »A – Oldest (Lower) »B – Middle Age »C – Youngest (Upper) –Actual age not known, only relative! Relative time – place in a sequence

3. Topic 1 – Telling Time 2. Absolute time – specific age –Example: Sedimentary Rock »Rock Layer B deposited 30 Ma (mega anna = million years ago) »B is 10 million years older than C »B is 5 million years younger than A Rock LayerAbsolute Age A35 Ma B30 Ma C20 Ma Two things told with absolute time 1. Actual age 2. Length of time between events -- used to determine rate of geologic process

4. So... What’s the story? List observations Do not write down interpretations

5. Finding Age with Relative Time Law of superposition – in a sequence of horizontal sedimentary rocks, the oldest in on the bottom Originally Horizontal Younger Timing Grand Canyon, Arizona, Copyright Larry Fellows http://www.earthscienceworld.org/imagebank/search/results.html?ImageID=hmwnq6 Older

6. Finding Age with Relative Time http://www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903page03.cfm

7. Finding Age with Relative Time What happened here? Originally layers deposited horizontally Then they were tilted USGS/Jennifer Loomis, TERCTilted limestone beds in the Mojave Desert, California http ://www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903page04.cfm.www.classzone.com/books/earth_science/terc/content/investigations/es2903/es2903page04.cfm

8. Finding Age with Relative Time Law of Cross-cutting relationships – igneous rocks are younger than rocks that they intrude into Cross- cutting MOST recent

9. Finding Age with Relative Time Law of (fragmented) Inclusion –Rock fragments found in another rock must be older than the rock it is found in Examples – pebbles in a conglomerate –Sand grains in a sandstone http://www.geology.sfasu.edu/rocks/conglomerate02.jp g http://www.zionnationalpark.com/zioninfo/photos/Sandstone-2.jpg

10. Finding Age with Relative Time Unconformity – break in the rock record –Eroded surface then buried –Parts of rock record missing like pages in a book –Gap in geologic time http://www.bamboo.hc.edu.tw/~sts/course-2003/course/textbook/text05/ch14/images/ch14-032.jpg

11. Geologic Time___________ ____________ http://www.astro.lsa.umich.edu/users/cowley/grand33.jpg 250 Ma 600 Ma TIMING: RELATIVE vs. ABSOLUTE

12. M. d’Alessio, 2004 Murder Mystery? How is this picture explained using relative dating? List observations From your observations make interpretations Law of Superposition Principles of: Original Horizontality Cross-Cutting Rel. Inclusions Unconformities

13. Topic 9 – Measuring Absolute Time http://home.earthlink.net/~colorado_hiking/1_Hiking_topics/pics/bristleconepineT.jpg 4,862 – Prometheus 4,767 -- Methuselah http://www.championtrees.org/champions/articles/AP21010.htm Tree rings can be used to measure specific dates –1 ring = 1 year –Width of ring correlates to temperature and rainfall –Wide ring = high temperature and rain –Oldest tree is the bristle cone pine

14. Radioactive Elements & Absolute Time Radioactive decay used to date much farther back in time Some elements naturally “decay” in the nucleus –Radioactive decay occurs until a stable element is formed http://www.pbs.org/wgbh/nova/first/radiocarbonce.html

15. Topic 12 – Half-Life Half-life = rate of decay –Time needed for ½ radioactive items to decay Ranges from seconds to billions of years Radioactive material Found inHalf-life (years) C-14Wood, peat, coal, bones, shells ~5,700 K-40Mica, feldspars~1.3 billion Rb-87Mica, feldspars~47 billion U-235Many rocks713 million U-238Oldest igneous rocks 4.5 billion

16. Fossil Preservation 1. Original Remains Frozen Resin (Amber) –Sticky substance from evergreens –Usually insects Tar Pits –LaBrea

17. Fossil Preservation Replaced Remains Hard parts replaced by minerals Usually done by groundwater –Ex: petrified Wood Mold or Cast Mold – shape of where fossil was Cast – new material fills mold & hardens –Ex: Shells

18. Fossil Preservation Trace Fossils Evidence of life other than remains –trails –Footprints –Burrows –copralites http://www.delargy.com/images/2004_7_Colorado/dinosaur%20footprint.JPG http://csd.unl.edu/csd-esic/ResourceNotesImages/volume16/page-24.jpg http://www.scienceviews.com/photo/thumb/SIA0651.jpg

19. Topic 5 – Fossils as Evidence for Evolution Oldest rocks with fossils show simple life forms (only) As time goes by, some simpler life forms become more complex This process of change is called: EVOLUTION Theory of Evolution: Scientific explanation for the past and present diversity of life http://www.thezreview.co.uk/posters/posterimages/e/evolution1.jpg

20. Topic 5 – Fossils as Evidence for Evolution Charles Darwin – “The Origin of Species”, 1859 - theory states that species evolve slowly over geologic time Modern science - species remain fairly constant for millenia, then abruptly change within a relatively short time, often less than 1 million years http://earth.ast.smith.edu/courses/ast215/darwin.jpg

21. Topic 6 – Index Fossils and Key Beds Index fossils (guide fossils) Lived for a “short geologic” time period in a lot of places Allow dating of rock layers with relative age 3 Characteristics 1. Easily recognized (unique) 2. Found over large geographic area –Continental drift theory evidence 3. Limited in time –Only lived over short period of time, therefore, only found in FEW rock layers http://www.paleocurrents.com/img/2002_09_13FI/HTML/138-3848_img_std.jpg

22. Topic 6 – Index Fossils and Key Beds Key Bed Single rock layer that acts like an index fossil Easily recognized Large area –Ex: Ash from volcanic eruptions Iridium layer from Chicxulub impact (K-T) http://www.astro.uva.nl/encyclopedie/images/chicxulub.gif Iridium Layer Clay with high rare element (Ir) found in Mexico, Italy, Denmark & New Zealand

23. Topic 7 – Rock Correlation Correlation: matching of rock layers from one area to another Index Fossils Key Beds Allow correlating over great distances Iridium Layer Clay with high rare element (Ir) found in Mexico, Italy, Denmark & New Zealand

24. Topic 8 – Other Uses for fossils 1. Determine relative age of rocks 2. Correlate rock layers 3. Indicate past climate Ex: coal only from warm, swampy areas 4. Oil exploration Microfossils – seen only with microscope Help correlate layers of rock to oil rich layers in other places

25. Topic 10 – Varves Varve Any sediment that shows a yearly cycle Sedimentary layers resemble tree rings Can date ~15,000 years ago –Often associated with lakes annual turnover

26. Geologic Timetable (p. 600-601) Eon – greatest division of geologic time Era – 2 or more of these form an eon Period – basic unit of geologic time in which a single type of rock system is formed (named for specific occurrence) Epoch – subdivision of a period Age – subdivision of an epoch –All changes based on significant changes in the fossil record The greater the changes, the larger division Fossil – ANY evidence of earlier life or environments preserved in rock record

27. Geologic Timetable The geologic time scale can be represented in many ways

29. Geologic Timetable

31. ERAAttributes Archean (Beginning Earth) Began ~4.6 Ga Beginning of Earth, almost no fossils Proterozoic (Earliest Life) Began 2.5 Ga Simple plants & animals (worms) No life on land Paleozoic (Ancient Life) Began 570 Ma Plant & Animal Fossils Land & Ocean Mesozoic Began 250 Ma Middle Life Age of Reptiles (dinosaurs) Cenozoic (Recent Life) Began 65 Ma Age of Mammals