The Age of the Earth How old is the Earth James Ussher o Age of the Earth 6 018 years old Based on biblical events in the Old Testament he found that the world was crated on October 23 rd 4004 BC at 9 a m Scientists calculations o Age of the Earth 4 6 billion years old Based on evidence found in rocks and radiometric dating Rocks and Geological Time Scale Oldest Rocks 4 0 billion years old Oldest Minerals 4 5 billion year old 540 million years ago Pre Cambrian beginning of life o The first evidence of fossilized life within rocks Time Scale o 14 billion years ago The Big Bang o 3 5 to 4 0 billion years ago earliest form of life o 100 000 years more or less modern human life Anthropocene most recent period of time in Earth history past few hundred years in which humans have significant global impact on the planet Paul Crutzen Geologic Time Holocene last 10 000 years since the end of the last Ice Age Geochronology the science of determining the age of rocks Nicholas Steno 1669 studied strata rocks to determine age o Principle of Superposition in any sequence of undisturbed strata of sedimentary rocks the oldest layer is on the bottom and the higher layers and younger o Sedimentary Rocks rocks formed from weathered products of pre existing rocks sediments that have been transported deposited and lithified converted into rock Principle of Uniformitarianism the physical chemical and biological laws that operate today have also operated in the geologic past Sequence of Geologic Events 1 Deposition 2 Folding and Uplifting 3 Erosion 4 Subsidence and Renewed Deposition Relative Age vs Absolute Age Absolute age of the Earth amount of time since the Earth solidified o When did the Earth cool and solidify into its present state from the hot molten rocky material it used to be Methods to Estimating the Age of the Earth Fossils and evolution Rates of deposition of sediments Cooling of the Earth from a molten state Radiometric Dating Principle of Parsimony Oscam s Razor Fossils remains of ancient life o Charles Lyell mid 1800s used evolution to estimate absolute ages of rocks He needed to find a natural process that leaves a tangible record in the rocks THEN he estimated the amount of time associated with such process SO the age of the rock can be estimated Lord Kelvin believed the earth was 10s of millions of years old o Based on cooling of the earth from molten state physics math Quantitative arguments o VS geologists and biologists who believed the earth was 100s of millions of years old based on fossils evolution intuition arguments Qualitative Radioactivity Cir 1890s proved that geologists and biologists were right o Radiometric dating o Radioactivity as an internal heat source Radiometric Dating Henri Becquerel AND Marie and Pierre Curie Phenomenon some elements are unstable and decay spontaneously o ex uranium As radioactive elements decay in the Earth they heat up the surrounding rocks o Kelvin didn t realize that there is a source of heat inside the earth due to the Earth s cooling radioactive decaying process The Earth took much longer to cool than Kelvin had thought Parent vs Daughter rate of decay o The more time passed the more daughter exists o The less time passed the more parent exists o Being in a state of molten rock begins the rate of decay clock Potassium Argon Dating K40 Proton becomes neutron Half life 1 3 billion years 19 e Ar40 18 or K40 Ar40 o If K40 Ar40 1 less than 1 3 billion years old o If K40 Ar40 1 more than 1 3 billion years old o If K40 Ar40 1 1 3 billion years old K Ar clock begins when K bearing minerals crystallize in a rock o The new material will contain K40 but NOT Ar40 because Ar40 does not combine with other elements o Uniformitarianism The Moon Craters on the moon meteors were created near the same time the Earth was Maria black holes water basins o Water doesn t actually exist on the moon o Black debris from volcanic eruptions Planets Active vs Dead o Radioactivity o Heat from within Smaller planets cool off faster Nebular Hypothesis o Planets formed from the collection of tiny particles that condensed out of a primitive nebula o German philosopher Immanuel Kant 1755 o French mathematician Pierre Simon La Place 1796