GEOLOGIC TIME, CONCEPTS, AND PRINCIPLES Sources: www.google.com en.wikipedia.org Thompson Higher Education 2007; Monroe, Wicander, and Hazlett, Physical orgs.usd.edu/esci/age/content/failed_scientific_clocks/ocean_salinity.html https://web.viu.ca/earle/geol305/Radiocarbon%20dating.pdf TCNJ PHY120 2013 GCHERMAN GEOLOGIC TIME, CONCEPTS, AND PRINCIPLES • Early estimates of the age of the Earth • James Hutton and the recognition of geologic time • Relative dating methods • Correlating rock units • Absolute dating methods • Development of the Geologic Time Scale • Geologic time and climate •Relative dating is accomplished by placing events in sequential order with the aid of the principles of historical geology . •Absolute dating provides chronometric dates expressed in years before present from using radioactive decay rates. TCNJ PHY120 2013 GCHERMAN TCNJ PHY120 2013 GCHERMAN Geologic time on Earth • A world-wide relative time scale of Earth's rock record was established by the work of many geologists, primarily during the 19 th century by applying the principles of historical geology and correlation to strata of all ages throughout the world. Covers 4.6 Ba to the present • Eon – billions to hundreds of millions • Era - hundreds to tens of millions • Period – tens of millions • Epoch – tens of millions to hundreds of thousands TCNJ PHY120 2013 GCHERMAN TCNJ PHY120 2013 GCHERMAN EARLY ESTIMATES OF EARTH’S AGE • Scientific attempts to estimate Earth's age were first made during the 18th and 19th centuries. These attempts all resulted in ages far younger than the actual age of Earth. 1778 ‘Iron balls’ Buffon 1710 – 1910 ‘salt clocks’ Georges-Louis Leclerc de Buffon • Biblical account (1600’S) 26 – 150 Ma for the oceans to become 74,832 years old and that as salty as they are from streams humans were relative newcomers. carrying low-concentrations of salt into an initially fresh-water ocean TCNJ PHY120 2013 GCHERMAN THE FOUNDERS OF MODERN GEOLOGY is considered to be the founder of modern geology. •Hutton first suggested that present day processes operating over long periods of time could explain all 1830 Principles of Geology geologic features. •Argued convincingly for Hutton's conclusions and established the •Hutton’s observations led to the principle of uniformitarianism as establishment of the principle of the guiding principle of geology . uniformitarianism . TCNJ PHY120 2013 GCHERMAN PRINCIPLES OF UNIFORMITARIANISM •This principle simply states that all investigations can assume that physical and chemical laws have operated through time, and the same processes which operate today (with allowance for varying rates), have also operated throughout Earth's history. TCNJ PHY120 2013 GCHERMAN PRINCIPLES OF UNIFORMITARIANISM Stephen Jay Gould (September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. He spent most of his career teaching at Harvard University and working at the American Museum of Natural History (NY). In the latter years of his life, Gould also taught biology and evolution at New York University. Gould's most significant contribution to evolutionary biology was the theory of punctuated equilibrium , which he developed with Niles Eldredge in 1972. Gould argued that Hutton's interpretation of uniformitarianism actually included a cyclical series of events in which all of Earth history was repeated with "repair" of the earlier age, much as many primal societies view time as a cyclical, rather than linear, phenomenon. Furthermore, the rates of geological processes were not required to be constant or gradual in either Hutton's or Lyell's concept of uniformitarianism. Similarly, catastrophism was not originally linked to a sequence of "special creations" or similar total recreation of the world geology and life. Instead, each sequence bounded by unconformities and containing a "new biosphere" was believed to be the result of a "revolution" which did not invoke any suspension of presently operating laws of nature. TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING •Relative dating is accomplished by placing events in sequential order with the aid of the principles of historical geology . •Six fundamental principles: 1) Superposition – undisturbed strata are younger on top and older on the bottom 2) Original horizontality – strata are deposited as flat, horizontal layers 3) Lateral continuity – strata are laterally continuous until they pinch out 4) Cross-cutting relationships – younger features cross-cut older features 5) Inclusions – fragments contained in rocks are older than the rock 6) Fossil succession - stratigraphic layers of the same age contain the same fossils TCNJ PHY120 2013 GCHERMAN 3 of 6 PRINCIPLES OF RELATIVE DATING ESTABLISHED BY NICOLAS STENO 1) Superposition – undisturbed strata are younger on top and older on the bottom 2) Original horizontality – strata are deposited as flat, horizontal layers 3) Lateral continuity – strata are laterally continuous until they pinch out •Observed the burial of organisms on flooplains by gravity-settled sediment. •Subsequent floods covered previous deposits. •Layers are laid-down essentially horizontal, and •Extend laterally until they either pinch out or terminate against the edge of the depositional basin boundary TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING (cont.) 4) Cross-cutting relationships – younger features cross-cut older features Basic dike cuts This principle is attributed to Fault cuts and offsets strata and country rock and is James Hutton who first realized the is therefore a relatively younger therefore a younger significance of unconformities at structure structure Siccar Point, Scotland TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING (cont.) 5) Inclusions – fragments contained in rocks are older than the rock • Sills have two baked margins and may have inclusions from the bounding beds • Lava flows on Earth’s surface and may have pieces ripped up and included in overlying detrital bed. •Only the bottom contact is baked. TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING 5) Inclusions – fragments contained in rocks are older than the rock Top - SS older than igneous activity basalt inclusion in a granite from Wisconsin Bottom - Granite older than SS TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING (cont.) 6) Fossil succession •An English civil engineer noticed while building a canal in England independently recognized the principle of superposition by reasoning that fossils seen in the excavation bottom were older than those in overlying, leading to the principle of faunal and flora succession. TCNJ PHY120 2013 GCHERMAN FUNDAMENTAL PRINCIPLES OF RELATIVE DATING 6) Fossil succession - Stratigraphic layers of the same age contain the same collection of fossils Section B contains the youngest rocks ‘key bed’ or ‘marker horizon’ Section C contains the oldest rocks TCNJ PHY120 2013 GCHERMAN SUMMARY OF PRINCIPLES OF HISTORICAL GEOLOGY •The principles of historical geology, in addition to uniformitarianism , are superposition, original horizontality, cross-cutting relationships, lateral continuity, inclusions, and fossil succession. •These principles are used to determine the sequence of geologic events and to interpret them. TCNJ PHY120 2013 GCHERMAN UNCONFORMITIES are surfaces of discontinuity in the rock deposition sequence which encompass significant periods of time . •Unconformities 1 Ma nondeposition may result from nondeposition and/or erosion . erosion 3 Ma 2 Ma TCNJ PHY120 2013 GCHERMAN UNCONFORMITIES 1) Disconformity – Surface separates parallel strata on either side 2) Angular unconformity – Surface separates strata tilted differently 3) Nonconformity – Surface cut into crystalline (igneous and/or metamorphic) rocks, then covered by sedimentary rocks TCNJ PHY120 2013 GCHERMAN UNCONFORMITIES Nonconformity Angular unconformity Disconformity TCNJ PHY120 2013 GCHERMAN RELATIVE DATING EXAMPLE TCNJ PHY120 2013 GCHERMAN RELATIVE DATING EXAMPLE solution TCNJ PHY120 2013 GCHERMAN STRATIGRAPHIC CORRELATION is the demonstration of equivalency of rock units from one area to another. Key beds are stratigraphic units such as coal beds or ash layers, that are sufficiently distinctive to allow identification of the same unit in different places or area. TCNJ PHY120 2013 GCHERMAN STRATIGRAPHIC CORRELATION An example of using key beds to correlate stratigraphic sections ~65 Ma from three National Parks Key bed 1: in the southwest USA Navajo Sandstone totaling over 400 Ma of rock succession > 1 Ba Key bed 2: ~550 Ma Kaibab Limestone TCNJ PHY120 2013 GCHERMAN GEOLOGIC TIME, CONCEPTS, AND PRINCIPLES • Good guide fossils have • Time equivalence is usually demonstrated rather short intervals of by the occurrence of similar fossils (guide existence fossils) in strata. Note the facies change but time equivalence TCNJ PHY120 2013 GCHERMAN TCNJ PHY120 2013 GCHERMAN TCNJ PHY120 2013 GCHERMAN THE K-T BOUNDARY MARKER HORIZON Cooling at this time is consistent with a global sea-level drop of ~40 m beginning in geomagnetic polarity chron 30n and ending in chron 28r, clearly spanning the K-T boundary. This event followed closely on a sharp sea-level drop and subsequent rise of ~30 m, coincident with the highest δ 18 O values recorded for the 30 My before or afterward, which occurred in the middle of chron 30n, ~1 My before the