Foothill High School Science Department The History of Life The Fossil Record

Foothill High School Science DepartmentFoothill High School Science Department

The History of LifeThe History of Life

The Fossil RecordThe Fossil Record


Fossils & Ancient LifeFossils & Ancient Life

• PaleontologistsPaleontologists– Scientists Who Study FossilsScientists Who Study Fossils– Infer What Past LifeInfer What Past Life• Looked LikeLooked Like• What They Ate & What Ate What They Ate & What Ate

ThemThem• BehaviorBehavior• Environment They Lived InEnvironment They Lived In

What They Looked Like


What They AteWhat They Ate


Behavior & EnvironmentBehavior & EnvironmentBehavior & EnvironmentBehavior & Environment

3.6 MYA3.6 MYA



• Fossil RecordFossil Record– Organization Of Fossils Organization Of Fossils

From Oldest To Newest From Oldest To Newest Including Supporting Including Supporting Information Of Other Life Information Of Other Life Forms In Their EnvironmentForms In Their Environment



Key ConceptKey ConceptThe Fossil Record Provides Evidence The Fossil Record Provides Evidence

About The History Of Life On Earth. It About The History Of Life On Earth. It Also Shows How Different Groups of Also Shows How Different Groups of Organisms Have Changed Over Time.Organisms Have Changed Over Time.



• Each Fossil Is Found Only In It’s Each Fossil Is Found Only In It’s Particular Time Period or LayerParticular Time Period or Layer

• A Kind Of Fossil ClockA Kind Of Fossil Clock• Of All The Life Forms That Have Of All The Life Forms That Have

Ever Lived On Earth -----Ever Lived On Earth -----– 99% Are Extinct99% Are Extinct• No Longer AliveNo Longer Alive


How Fossils Are FormedHow Fossils Are Formed

• Most Form In Sedimentary Most Form In Sedimentary RockRock

• Plants & Animals Die In A Plants & Animals Die In A Water Environment And Are Water Environment And Are Covered With SiltCovered With Silt

• Others Covered With Fine Others Covered With Fine Sand or Volcanic AshSand or Volcanic Ash

• Compressed Into RockCompressed Into Rock


How Fossils Are FormedHow Fossils Are Formed

• Organic Materials Are Replaced By MineralsOrganic Materials Are Replaced By Minerals• Quality Of Preservation VariesQuality Of Preservation Varies• Fossils Include:Fossils Include:– BonesBones– EggsEggs– FootprintsFootprints– Skin Impressions, etc.Skin Impressions, etc.


Interpreting Fossil EvidenceInterpreting Fossil Evidence

• Fossils Are Released ByFossils Are Released By– Tectonic ForcesTectonic Forces– ErosionErosion–MiningMining– ConstructionConstruction


Interpreting Fossil EvidenceInterpreting Fossil Evidence

• Most Fossils DisarticulatedMost Fossils Disarticulated– PredationPredation– ScavengersScavengers– RotRot

• Catastrophic Events May Bury & Catastrophic Events May Bury & Preserve Whole Animals and/or Preserve Whole Animals and/or EcosystemsEcosystems


Life On EarthLife On Earth


Dating FossilsDating Fossils

Two Types of DatingTwo Types of Dating1.1. Relative DatingRelative Dating

Organizes Fossils By Order (1Organizes Fossils By Order (1stst, 2, 2ndnd, 3, 3rdrd, etc.), etc.)Tells You Which Organisms Lived In What OrderTells You Which Organisms Lived In What OrderDoes Not Give You Actual YearsDoes Not Give You Actual Years

2.2. Absolute DatingAbsolute DatingGives You Age In Years Before PresentGives You Age In Years Before Presente.g. 150 Million Years Agoe.g. 150 Million Years Ago


Relative DatingRelative Dating





• The Age of a Fossil Is Determined By The Age of a Fossil Is Determined By Comparing Its Placement With Other Comparing Its Placement With Other Fossils In Other Layers Of Sedimentary Fossils In Other Layers Of Sedimentary RockRock– Allows Comparison Of Layers World WideAllows Comparison Of Layers World Wide



• Index FossilsIndex Fossils– Easily RecognizedEasily Recognized– Existed For A Short (?) Existed For A Short (?)

PeriodPeriod–Wide Geographic Wide Geographic

DistributionDistribution–Does Not Give Absolute Does Not Give Absolute

AgeAge



Key Concept:Key Concept:

Relative Dating Allows Relative Dating Allows Paleontologists To Estimate A Paleontologists To Estimate A Fossils Age Compared With That Fossils Age Compared With That Of Other FossilsOf Other Fossils


Radioactive DatingRadioactive Dating

Uses The Half Lives Of Certain Radioactive Uses The Half Lives Of Certain Radioactive Isotopes In Isotopes In IgneousIgneous Rocks To Calculate The Rocks To Calculate The

Age Of A FossilAge Of A Fossil

Half LifeHalf LifeThe Length Of Time Required For Half Of The Length Of Time Required For Half Of

The Radioactive Atoms In A Sample To The Radioactive Atoms In A Sample To Decay Decay



Key Concept:Key Concept:In Radioactive Dating, Scientists In Radioactive Dating, Scientists

Calculate The Age Of A Sample Based Calculate The Age Of A Sample Based On The Amount Of Remaining On The Amount Of Remaining Radioactive Isotopes It ContainsRadioactive Isotopes It Contains



Different Radioactive Elements Have Different Radioactive Elements Have Different “tick rates”Different “tick rates”

Carbon-14Carbon-14Half-life = Half-life = 5,730 years5,730 yearsDecays to Nitrogen-14Decays to Nitrogen-14

Useful Back 60,000 yearsUseful Back 60,000 years

Absolute Age Radioactive Dating

IsotopeIsotope StableStableDaughterDaughter

ParentParentHalf-Life (years)Half-Life (years)

RangeRange(years)(years)

SampleSampleMaterialMaterial

Carbon 14Carbon 14 Nitrogen 14Nitrogen 14 5,7305,730 20 to 60,00020 to 60,000 Carbon Bearing Carbon Bearing Plants, AnimalsPlants, Animals

Potassium 40Potassium 40 Argon 40Argon 40 1.3 Billion1.3 Billion 50,000 to50,000 to4.6 Billion4.6 Billion

Volcanic igneous Volcanic igneous rocks; micas, rocks; micas,

feldspars, hornblendfeldspars, hornblend

Rubidium 87Rubidium 87 Strontium 87Strontium 87 48.8 Billion48.8 Billion 10 Million to10 Million to4.6 Billion4.6 Billion

Metamorphic and Metamorphic and igneous rocks; igneous rocks;

feldspars, micas, feldspars, micas, hornblendhornblend

Thorium 232Thorium 232 Lead 208Lead 208 14 Billion14 Billion 10 Million10 Million Zircon, Uranium & Zircon, Uranium & ThoriumThorium

Uranium 235Uranium 235 Lead 207Lead 207 704 Million704 Million 4.6 Billion4.6 Billion

Uranium 238Uranium 238 Lead 206Lead 206 4.5 Billion4.5 Billion


Geologic Time ScaleGeologic Time Scale

Developed By Paleontologists To Classify Developed By Paleontologists To Classify Geologic And Biologic EventsGeologic And Biologic Events

Rock LayersRock LayersFossils PresentFossils Present

Documents

Foothill High School Science Department The History of Life The Fossil Record