Harlow Shapley, who wrote an article in on the subject, was an astronomer, responsible for the detection of the redshift in distant nebulae and hence, indirectly, for our present concept of an expanding universe. Russell, author of the article on radioactive dating, was familiar to me for his part in developing the Hetzsprung-Russell diagram for stars, but I was surprised to discover that he was also the Russell of Russell-Saunders coupling, important in atomic structure theory.
Sollas , assumed that physical processes would eventually be discovered to power the great engine of erosion and uplift. The second act of the drama sees a prolonged attempt by a new generation of geologists to estimate the age of the earth from observational evidence, to come up with an answer that would satisfy the demands of newly dominant evolutionary thinking, and to reconcile this answer with the constraints imposed by thermodynamics.
The third act sees the entry of a newly discovered set of physical laws—those governing radioactivity. Lord Kelvin and his allies used three kinds of argument.
The first of these referred to the rate of heat loss from the earth and the length of time it would have taken to form its solid crust. The second referred to such topics as the detailed shape of the earth bulging slightly at the equator and the dynamics of the earth-moon system. The third referred to the heat of the sun, particularly the rate at which such heat is being lost, compared with the total amount of energy initially available. The first argument was completely undermined after taking into account the amount of heat generated by radioactive decay.
The second depended on highly dubious theories of formation of the earth and moon and plays relatively little role in this compilation. The third, which by the end was the most acute, presented a problem that outlasted the controversy itself. He did not need to wait long. In Sir Arthur Eddington came up with the answer: the fusion of hydrogen into helium. One referred to the depth of the sediments and the time they would have taken to accumulate; the other referred to the salinity of the oceans, compared with the rate at which rivers are supplying them with sodium salts.
In hindsight, both theories were deeply misguided, for similar reasons. Scientists have dated these rocks using uranium-lead isotopes at 4. Also, scientists recently reported 4. Narryer and the Jack Hills in Western Australia Nutman , which suggests the erosion of granite-like crust older than the oldest known preserved crust Cooper Thus, we can be confident that the minimum age for the Earth exceeds 4 billion years by examining Earth materials.
It overlaps with the 4. Annual rotations of the stars in the Universe were noted by many civilizations. Universe was considered ageless, without beginning and end. Time therefore was loop of cycles. The Vedic ages are named Satya, Treta, Dvapara, and Kali; each one declines in moral excellence due to an increasing deficiency of Dharma.
At the top of the cycle, is the Golden Age or Satya truth Yuga, a period of 1,, years four Kali yugas where the human life span is , years; Then comes the Treta, 1,, years three Kali yugas where the human life span is 10, years; Next is the Dvapara Yuga, , years two Kali yugas where the human life span is years; Last comes the Kali Yuga, , years where the human life span is years.
One thousand Maha yugas — 4,,, years by human count — constitute one day, or Kalpa, for Brahma which begins with Sristi, the emanation of a universe out of the Divine; and terminates with Pralaya, re-absorption back into the Divine. Brahma lives for Brahma years of Brahma days and nights and concludes with universal dissolution of all three worlds of being earth, heaven and the space between , even the highest worlds.
Re-absorption prevails for another Brahma years, after which the entire cycle ,,,, human years begins again. What is interesting from the above information is that one day of Brahma equal to 4. Skip to main content. Scientists measure how much of the parent element still exists in a rock or mineral.
This comparison tells them how much time has passed since the rock formed. What element they choose to measure depends on many factors. It also depends on whether the rock had been heated or chemically altered in the past.
The decay of potassium to argon, uranium to lead, and one isotope of lead to another are some common yardsticks used to date very old rocks. These dating methods allow scientists to put real ages on rocks with astonishing accuracy. The exact timing and even the names of some geologic divisions are still not set in stone. Every year, geochronologists GEE-oh-kron-OL-oh-gizts — scientists who specialize in dating geologic ages — improve the methods to zoom in more accurately.
They can now distinguish events that occurred just a few thousand years apart, back tens of millions of years ago. Rivers move gravel and clay that will someday become rock. Volcanoes spew out new lava. These deposits slowly add layers that will end up marking the current geologic period. And now that people have been around for the equivalent of 12 seconds, some geologists propose adding a new period to the Geologic Time Scale.
It will mark the time since humans began altering Earth. Starting about 10, years ago, it is tentatively being called the Anthropocene. Its geologic layers will be quite a mix. They will hold plastics, petrified food wastes, graveyards, discarded cell phones, old tires, construction debris and millions of miles of pavement.
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