2Relative DatingIs a series of Principles and lawsThe Doctrine of UniformitarianismPrinciple of Original HorizontalityLaw of SuperpositionLaw of Cross-cutting relationshipsLaw of Inclusions
3Doctrine of Uniformitarianism Proposed by James Hutton in 1700’s.The present is the key to the past.States that the physical, chemical and biological process that occur today have occurred throughout the Earth’s history.The process have not changed, but the rates and intensities at which they occur can change.
4Principle of Original Horizontality 1st proposed by the Danish geologist Nicholas Steno ( )This applies to sedimentary rocks.Sediments when deposited form horizontal layers.If we see sedimentary rocks that are folded or inclined, we can assume that something has occurred after the sediments were deposited.
6Law of Superposition1st proposed in the 11th century by the Persian geologist, Avicenna (Ibn Sina), and later formulated more clearly Nicolas StenoThis applies to Sedimentary rocks.Each layer is a bed. The oldest is at the bottom, and the youngest is at the top.Each layer of rock represent a specific period in time.
7Law of Cross-Cutting Relationship. If a layers cut diagonally through another then the diagonal layer is younger.The layer that is cutting through another has to be younger because the original layer had to be there before the newer one could cut through it.
8Law of Superposition & Cross-Cutting Relationship
9Law of InclusionInclusions are pieces of one rock that is contained within another.Consequently, the one the pieces are from is older than the one the pieces are in.
10This is a gap in the geologic record. UnconformityThis is a gap in the geologic record.Occurs when sedimentation stops because the area is above sea level, thus no sediments can be deposited.i.e. - this location was once the surface of the Earth.They can be Disconformity (Sedimentary Rock) or Nonconformity (Igneous or Metamorphic Rocks)
11Sedimentary layers are parallel above and below the erosional contact. 124356
12NonconformityOlder Igneous or Metamorphic rocks are separated from younger Sedimentary layers.Uplift and erosion of overlying rocks had to occur.Once these rocks are on the surface, they are weathered and erosion take place.After erosion sedimentation occurred.
13Nonconformity K Q J P IM Deposition of rocks Uplift, & erosion J & K. Intrusion orMetamorphism ofRock IMUplift, & erosionOf rocks J,K,& IMSubsidence & Depositionof rocks P & QSea LevelNonconformityKJIMPQ
14Development of Angular Unconformity When the angle of the rock below is different then the angle of the rocks above.During the pause in sedimentation, folding and or tilting has occurred.
15Faults A movement of rock . The movement has to be younger then the rock it cuts through.
16Absolute Dating Quantify the date in years. We use fossils and Radiometric Dating (half lives) to determine the age of a layer.
17Fossils and Principle of Fossil Succession Fossils - evidence of past life.For fossils to occur you must have a rapid burial; if not the remains will be destroyed.Bones, shells make good fossils.We know that different organisms lived during the same time; if one is found then the other should be found in the same layerUsed for relating age of rocks regardless of depth or distance apart.
20Principles of Radiometric Dating Discovered in 1896 by Henri Becquerel.Radioactive Decay- radioactive materials break down into other materials at known rates.Radioactive parent elements decay to stable daughter elements. (Carbon14 → Carbon12)Once this rate is known, geologists can estimate the length of time over which decay has been occurring.
22Types of Radiometric Dating Radiocarbon dating - Measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.Uranium-lead dating - Measures the ratio of two lead isotopes (lead-206 and lead-207) to the amount of uranium in a mineral or rock.This method is one of the two most commonly used (along with argon-argon dating) for geologic dating, applied to samples older than about 1 million years.Uranium-thorium dating - Used to date corals, carbonates, and fossil bones. Its range is from a few years to about 700,000 years.Potassium-argon and argon-argon dating - These techniques date metamorphic, igneous and volcanic rocks, for samples older then a few thousand years.
23Geologic Scale The largest time unit Eon Era Period EpochEraPeriodThe largest time unitThe smallest time unit
25Geologic Timeline Precambrian Eon Three Eras 4.5 Billion-to 540 million years agoNo life forms to multi cell organismsPhanerozoic EonPaleozoic Era (Ancient Life)540 million years ago to 248 million years agoMarine invertebrates dominant then undergo mass extinctionOn land, insects evolveMesozoic Era (Middle Life)The age of Reptiles 248 million years ago - ~65 million years agoPangea & early dinosaursMass extinction of dinosaurs and early trees bloom.
26Cenozoic Era (Recent Life) 2 periods Tertiary & QuaternaryTertiary Period: (Age of Mammals)~65 to ~2.6 million years agoMammalian life diversifies to all modern mammals presentQuaternary period (Humans Develop)~2.6 million years ago to the presentThe oldest species of Homohabilis evolves to Human civilization develop.