A Billion Years: My Escape from a Life in the Highest Ranks of Scientology

Product Information

In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. [19] [20] He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value. His calculations did not account for heat produced via radioactive decay (a then unknown process) or, more significantly, convection inside Earth, which allows the temperature in the upper mantle to remain high much longer, maintaining a high thermal gradient in the crust much longer. [19] Even more constraining were Kelvin's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Kelvin estimated that the Sun is about 20 million years old. [21] [22] William Thomson (Lord Kelvin) Stearns, Beverly Peterson; Stearns, S.C.; Stearns, Stephen C. (2000). Watching, from the Edge of Extinction. Yale University Press. p.preface x. ISBN 978-0-300-08469-6. Lindsey, Rebecca; Morrison, David; Simmon, Robert (March 1, 2006). "Ancient crystals suggest earlier ocean". Earth Observatory. NASA . Retrieved April 18, 2012.

Photosynthetic organisms appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, and culminated in the Cambrian Explosion about 538.8 million years ago. This sudden diversification of life forms produced most of the major phyla known today, and divided the Proterozoic Eon from the Cambrian Period of the Paleozoic Era. It is estimated that 99 percent of all species that ever lived on Earth, over five billion, [18] have gone extinct. [19] [20] Estimates on the number of Earth's current species range from 10 million to 14 million, [21] of which about 1.2 million are documented, but over 86 percent have not been described. [22] However, it was recently claimed that 1 trillion species currently live on Earth, with only one-thousandth of one percent described. [23]a b c Boltwood, B. B. (1907). "On the ultimate disintegration products of the radio-active elements. Part II. The disintegration products of uranium". American Journal of Science. 23 (134): 77–88. doi: 10.2475/ajs.s4-23.134.78. S2CID 131688682. The boundary between avian and non-avian dinosaurs is not clear, but Archaeopteryx, traditionally considered one of the first birds, lived around 150Ma. [177] In the same way, during the Snowball Earths most of the continental surface was covered with permafrost, which decreased chemical weathering again, leading to the end of the glaciations. An alternative hypothesis is that enough carbon dioxide escaped through volcanic outgassing that the resulting greenhouse effect raised global temperatures. [142] Increased volcanic activity resulted from the break-up of Rodinia at about the same time. [144] An age of 4.55 ± 0.07 billion years, very close to today's accepted age, was determined by Clair Cameron Patterson using uranium–lead isotope dating (specifically lead–lead dating) on several meteorites including the Canyon Diablo meteorite and published in 1956. [42] Lead isotope isochron diagram showing data used by Patterson to determine the age of Earth in 1956.

In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the universe [ citation needed]. Lomonosov's ideas were mostly speculative [ citation needed]. In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75,000 years old. [18]Thus, Arthur Holmes' report concluded that radioactive dating was the only reliable means of pinning down geological time scales. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations. [ citation needed] Modern radiometric dating Kleine, T.; Palme, H.; Mezger, K.; Halliday, A.N. (2005). "Hf-W Chronometry of Lunar Metals and the Age and Early Differentiation of the Moon". Science. 310 (5754): 1671–1674. Bibcode: 2005Sci...310.1671K. doi: 10.1126/science.1118842. PMID 16308422. S2CID 34172110.