Age of Earth Flashcards
two distinct process of estimation to determine the age of the earth
- Dating of geological formations and geological events by indirect methods (relative age)
- Radioactive methods
Includes various processes of determining the age. attempts were made to determine the age of the earth from the evolutionary changes of animals
Indirect Methods
Uses the fine sedimentary deposits of glacial origin which represents the annual accumulation of the layers marked by variation in color and gradation in the size of materials constituting the layers.
0-10,000 YEARS ONLY
Varve-clock Method
The average annual rate of deposition of sediments and the thickness of all strata deposited during the whole geological history are taken into account. This method is full of imperfections and variations from place to place, the age of the cambrian as determined by this and other accurate methods closely approach each other.
Sedimentation-Clock Method
All the salts of the seas of today have been acquired from the land by its erosion and weathering thru ages. By determining the yearly rate of increase of salinity the age of the earth was calculated to be 100 my by Joly
Salinity-Clock Method
Assuming the initial temp of the earth to be 3900 C, Kelvin determined the age of earth to be 20 to 400 my, full of imperfections since the generation of radioactive heat and other factors were not taken into account
Rate of the cooling of the earth
First formed animals were unicellular and and multi-cellular with more complexities came into being gradually and man is considered to be the most evolved one
Evolutionary changes of animals
” a radioactive parent element decays into a stable daughter element at a constant rate”
Radioactive Methods
U 238 and U 235 are two isotopes used ; half lives which are 4498 my and 713 my respectively
Uranium-lead Method
Rb 87 yields Sr 87 and its half-life is about 50my.
Valuable method for metamorphic rocks and pre-cambrian rocks
Rubidium- Strontium Method
Thorium 232 yields lead 208 thru radioactive decay and the half-life of thorium is 13,900 my
Thorium lead Method
Potassium is having 3 isotopes like K39, K40, K41, but only K 40 is radioactive. The half-life of K40 to convert itself in Ar40 is 11,850 my
Potassium-argon Method
The carbo-14 is radioactive with a half-life of 5570 years. All organisms take in C14 and a constant level of this isotope is maintained by all living organisms. This method is useful for dating relatively recent materials up to 70,000 years ago.
Radio-carbon method
Up to what range of years does radioactive methods estimates?
4500MYA to 4.5BYA
