8 Other laws of relative dating: Principle of Inclusions – fragments rock contained within a body of rock must be older than the “host” rockEx. ConglomeratePrinciple of Faunal Successions – specific fossils follow one another in a specific orderEx. Dinosaur fossils in both Montana and China
9 Determining Absolute Age of Rocks radioactive decay: over time, radioactive elements release a proton(s) to make a new, lighter, more stable element.
10 Major isotopes used for Radiometric Dating: U 238 Pb 206U 235 Pb 207Th 232 Pb 208
11 Radioactive elements decay at CONSTANT rates half-life: the time it takes for ½ of the atoms of a radioactive element to decay
12 Major isotopes used for Radiometric/Absolute Dating: ParentDaughterHalf-LifeU – 238Pb – 2064.5 billion yearsU – 235Pb – 207713 million yearsTh – 232Pb – 20814.1 billion years
13 C-14 dating: used only to date things that were once alive - half-life is only 5800 years; C-14 decays into N-14 - can date more recent remains (up to about 50,000 years)
14 Other dating techniques: Dendrochronology: counting rings on treesRings look different in times of drought and other extreme climate conditionsVarve chronology – looking at glacial sediments in lake bedshelps us find weather patterns for studying global warming
15 fossil: the remains or traces of organisms that lived long ago What is a fossil?fossil: the remains or traces of organisms that lived long ago
16 Formation of a dinosaur fossil: Fossils can form in various ways.Typically, the body material is replaced by minerals.
17 Mold & Cast Formation Process Organism becomes encased in sediment that is compressing to form a rock.Water gradually dissolves organism.
18 This leaves a hole in the rock shaped like the organism – a mold Water carries minerals that recrystallize in the mold making a cast
19 Replacement of Minerals: Water partially or completely dissolves an organism, depositing minerals (like quartz) in its place.Minerals are actually harder than the original bone.
20 trace fossil: evidence of life other than the remains of plants or animals ex. footprints, tracks, burrows
21 index fossil: fossils that are found over a wide geographic area but lived over a narrow range of time - help to identify the relative age of the rock in which they occur
22 The Geologic Timetable era: a long time segment defined by dominant life formsEras are broken down into segments called periods.
23 period: a subdivision of an era epoch: a subdivision of a period
24 The Earth is 4.6 billion years old How do we know?Oldest “Earth” rocks found are about 3.5 billion years oldMoon rocks (no plate tectonics/no recycling of rock) taken during the lunar landing have been dated at 4.53 billion years oldMeteorites (remnants of our early solar system) have been dated at 4.6 billion years
25 PRECAMBRIAN TIMEFrom beginning (4.6 billion years ago) to 545 million years ago (mya)Makes up 90% of Earth’s history
26 many rocks eroded significantly main life form was cyanobacteria (photosynthetic bacteria)
27 cyanobacteria added large amounts of oxygen (through photosynthesis) to the atmosphere... made it possible for other life (plants and animals) to evolve
28 PALEOZOIC ERA “The Age of Invertebrates” From 545 mya to 245 mya (about 300 million years ago)
29 Divided into 6 periods Cambrian Ordovician Silurian Devonian – Age of FishesCarboniferous – Age of AmphibiansPermian – largest mass of extinction of recorded life
30 In the US, the carboniferous period is divided into the Upper Carboniferous or PennsylvanianLower Carboniferous or Mississippian
31 warm, shallow seasPennsylvania was underwaterNorth America was at the equator
32 Marine life forms:trilobites - relative of horseshoe crabbrachiopods - look like clamscrinoids - relative of starfish