Geologic Time Scale and Origin of Life PDF

Geologic Time and Origin of Life Geological Time Is Vast Time is the dimension that sets geology apart from most other sciences. Geological time is vast, and Earth has changed tremendously during this time. Even though most geological processes are very, very slow, the vast amount o...

Geologic Time and Origin of Life Geological Time Is Vast Time is the dimension that sets geology apart from most other sciences. Geological time is vast, and Earth has changed tremendously during this time. Even though most geological processes are very, very slow, the vast amount of time that has passed has allowed for the formation of extraordinary geological features. Geological Time Is Vast We have numerous ways of measuring geological time. We can tell the relative ages of rocks: - based on their spatial relationships, - we can use fossils to date sedimentary rocks because we have a detailed record of the evolution of life on Earth, and - we can use a range of isotopic techniques to determine the absolute ages (in millions of years) of igneous and metamorphic rocks. Geologic Time Scale Relative dating – placing geologic events in sequential order as determined from their positions in the geologic record. – does not tell how long ago a particular event took place, only that one event preceded another. Numerical dating – provides specific dates for rock units or events expressed in years before the present. Radiometric dating is the most common method of obtaining numerical ages. Dates are calculated from the natural rates of decay of various radioactive elements present in trace amounts in some rocks.  Today, the geologic time scale is really a dual scale — a relative scale based on rock sequences with radiometric dates expressed as years before the present. Early Concepts of Geologic Time and Earth’s Age James Ussher Georges Louis (1581–1656) de Buffon (1707–1788) Archbishop of Armagh, French Ireland zoologist he asserted assumed that Earth gradually that God cooled to its created Earth present on Sunday, condition from October 23, a molten 4004 BC beginning James Hutton works Scottish geologist founder of modern geology principle of uniformitarianism “The present is the key to the past.” viewed Earth history as cyclical recognized the importance of unconformities in his cyclical view of Earth history James Hutton works Siccar Point, Scotland Hutton observed steeply inclined metamorphic rocks that had been eroded and covered by flat-lying younger rocks Hutton was the first to understand and explain the significance of such gaps in the geologic record Lord Kelvin (1824–1907) William Thomson, 1st Baron Kelvin a highly respected English physicist, mathematician, and engineer professor of Natural Philosophy at the University of Glasgow in 1866, claimed to have destroyed the uniformitarian foundation on which Huttonian– Lyellian geology was based Lord Kelvin (1824–1907) with the belief that Earth was originally molten, Kelvin assumed that it has gradually been losing heat and that, by measuring this heat loss, he could determine Earth’s age by knowing the size of Earth, the melting temperature of rocks, and the rate of heat loss, Kelvin calculated the age at which Earth was entirely molten Earth could not be older than 400 million years or younger than 20 million years Lord Kelvin (1824–1907) Kelvin was unaware that Earth has an internal heat source—radioactivity— that has allowed it to maintain a fairly constant temperature through time His “unquestionable calculations” were no longer valid, and his proof for a geologically young Earth collapsed Modern View of Uniformitarianism Geologists today assume that the principles, or laws, of nature are constant but that rates and intensities of change have varied through time. Some geologists prefer to use the term actualism instead of uniformitarianism to remove the idea of “uniformity” from the concept Relative Dating Methods Six fundamental geologic principles are used in relative dating: - superposition, - original horizontality, - lateral continuity, - cross-cutting relationships, - inclusions, and - (fossil) or faunal succession Nicolas Steno Danish anatomist Niels Stensen (1638–1686) native of Copenhagen, Denmark Steno's work on the formation of rock layers and the fossils they contain was crucial to the development of modern geology includes superposition, original horizontality, lateral continuity Cross-cutting relationships originally developed by James Hutton in Theory of the Earth (1795) and embellished by Charles Lyell in Principles of Geology (1830), the principle of cross-cutting relationships states that the geologic feature which cuts another is the younger of the two features Principles of Inclusion and Faunal Succession Sir Charles Lyell (1797–1875) was a great geology teacher and interpreter. he explained what we now call the principle of inclusions, known as the principle of inclusions and components. by discerning that a rock fragment inside another rock mass is older than the rock mass enclosing it Principles of Inclusion and Faunal Succession William ‘Strata’ Smith he discovered that fossils could be used to correlate rocks of the same age credited with creating the first detailed, nationwide geological map of any country Smith’s great geologic map of England and Wales (1815) set the style for modern geologic maps credited with formulating the principle of faunal succession Principles of Inclusion and Faunal Succession The principle of inclusions states that any rock fragments that are included in rock must be older than the rock in which they are included. The principle of faunal succession states that there is a well-defined order in which organisms have evolved through geological time, and therefore the identification of specific fossils in a rock can be used to determine its age. Origin of Life Theories Abiogenesis Miller-Urey experiment Submarine Hydrothermal Vents and the Origin of Life Meteorites and extra-terrestrial origin of life / Panspermia Earth’s Oldest Known Organisms - prokaryotic cells to eukaryotic cells; archaea - stromatolites Importance of Banded Iron Formations Additional Notes: Numerical dating Radioactive decay is the process whereby an unstable atomic nucleus is spontaneously transformed into an atomic nucleus of a different element. The half-life of a radioactive element is the time it takes for one-half of the atoms of the original unstable parent element to decay to atoms of a new, more stable daughter element. The half-life of a given radioactive element is constant and can be precisely measured. Half-lives of various radioactive elements range from less than a billionth of a second to 106 billion years. END