History Of The Earth PDF

the 17th to 19th centuries based upon the work of Steno, ☞ Is concerned with the James Hutton, and William development of the Planet Earth...

the 17th to 19th centuries based upon the work of Steno, ☞ Is concerned with the James Hutton, and William development of the Planet Earth Smith. from its formation to the ☞ As early as the mid 1600’s, present day. Nicholas Steno, a Danish ☞ In order to tackle Earth’s history, Scientist studied the relative position of sedimentary rocks. Scientist utilized methods to refer to the time periods in which events happened, and organisms ☞ He found that solid particles thrived. settles according to their relative weight or size. ☞ With the information they gathered from fossil evidence and ☞ The largest and heaviest rocks and applying Nicholas settles first; the smallest and Steno’s Principle’s, they were able lightest is the last one to settle. to create a listing of rock layers from older to youngest. ☞ Slight changes in particles size or composition results in the ☞ Then they divided the History of formation of layers. Earth into blocks of time with each block characterized by important events. ☞ Sedimentary rocks are formed particles by particles and layer by ☞ Most sediments when deposited, ☞ Sedimentary rock, also called layer. form a horizontal or nearly stratified rock, is formed over time horizontal layers. by wind, rain and glacial ☞ The layer are piled on top of the formations. other. ☞ This means that if there are non- ☞ The characteristics of rocks horizontal layers they could have ☞ Rock layers are also called been tilted or folded from their show a record of events that strata and stratigraphy is the original horizontal position by happened involving them. science of rock strata or layers. events such as episodes of mountain building. ☞ But if you just consider one rock ☞ Layering occurs in sedimentary it will give you very limited rocks as they accumulate information. Instead, what through time, so rock layers hold happened in the past can be the key in learning about the explained by examining the cross environment of long ago ----- in section of large masses of rocks unlocking the successive events in their particular location. of the Earth’s historical past. ☞ We shall use the term “Rock Formation” ☞ Are basic principles that all geologist use in deciphering the age and characteristics of rock layers. ☞ Rock layers, as originally laid down, are bounded by the edge of ☞ These laws were developed in the basin of deposition.  that the same vertical changes in layers, producing an angular ☞ Layers of sedimentary rocks the fossils that are embedded in discordance with the overlying extend sideways in the same order. rocks occurred in different places. horizontal layers. ☞ A later event such as river ☞ He recognized that fossil cutting may form a gap, but the groups were succeeded by other connection between strata can fossil groups through time. still be established. The point is ☞ The oldest rock in the Grand that scientist can relate layers at ☞ A kind of living thing had Canyon that are exposed at the one location to layers at another succeeded another when its base are Proterozoic-age rocks. location. population increased after the population of the other kind disappears from the Earth. ☞ This is an appreciation of the ☞ This is critical for stratigraphic principle of superposition. correlation. ☞ This allowed geologist to develop a fossil stratigraphy ☞ In a pile of sediments, the and provided a means to oldest deposits are at the bottom correlate rock throughout the world. and on top are the younger deposits. ☞ Each major layer of sedimentary rocks in the Grand Canyon contains different kind of fossils. ☞ The Grand Canyon serves as a very good example of the principles ☞ The succession of fossils is ☞ As undisturbed layers of stratigraphy. consistent everywhere in the accumulate through time; older canyon and is also like the layers are buried beneath ☞ The Grand Canyon Spectacularly succession of fossils in the other younger layers. exposes rocks spanning parts of North America and on hundreds of millions of years of other continents. ☞ This principle also states that Earth’s History. rock fragments must be older than the rock containing the fragments. ☞ Many of the rock layers exposed ☞ This is an appreciation of the on the walls of the Grand Canyon principle of faunal succession. were left undisturbed by mountain building or any other form of deformation ever since they were ☞ The principle has also been used laid down on the Earth Surface. to recognize the that the Grand Canyon includes rocks ☞ This is an appreciation of the from the Cambrian, Devonian, principle of Horizontality. Permian and other geologic periods, each characterized by ☞ Some older layers, however, different fossils. have been tilted and the surface where these tilted layers are overlaid by a stratum that is not deformed is called angular unconformity. ☞ Dating Techniques are ☞ The principle was developed by procedures used by scientist to determine the age of rocks. William Smith, an English Engineer in the late 1700s. ☞ An angular unconformity is an unconformity where horizontally ☞ Geologist establish the age of ☞ Smith noticed succession of parallel strata of sedimentary rock Rocks in two ways: Relative are deposited on tilted and eroded dating and Absolute Dating. rocks layers; furthermore, he saw  ☞ To correlate means to link and examining which species or genera of animals are buried in match in time rocks from different it. places. ☞ Correlations can be made by ☞ The technique works best if tracing rock strata from one area the animals belonged to species to another using the Principle of that evolved quickly, expanded Lateral Continuity or by relating rapidly over a larger area or the fossils of the two areas using suffered a mass extinction. the Principle of Faunal Succession. ☞ Faunal analysis can ☞ Relative dating requires an provide relative ages for materials buried in extensive knowledge of the faunal encasing stratigraphic succession, a term layers. for the way strata are built up and changed by geologic process. ☞ Stratigraphic ranges ☞ By studying the strata, and origins of some major groups of Geologist and paleontologist animals and plants. interpret the strata formation to ☞ Is used to arrange geological learn about the environment long events and the rocks they leave time ago. behind in a sequence. It is based on the Principle of Superposition ☞ If the sediment layer is thick, which enables scientist to arrange geological events in order. the climate was stable. ☞ Rock succession are ☞ When new layers appear in the sequences of rocks that are strata, a change occurred. established by the order in which ☞ Radioactivity – Emission of they are deposited. Ionizing Radiation or particles caused by the spontaneous ☞ Relative dating cannot specify disintegration of Atomic Nuclei. the absolute age, whether one rock is older or younger. ☞ Ionizing radiation - is a type of energy released by atoms that ☞ The relative age of a rock is travels in the form electromagnetic determined by its position within waves (gamma or X-rays) or the strata. particles (neutrons, beta or alpha). ☞ The spontaneous disintegration of atoms is called radioactivity, and the excess energy emitted is a form of ionizing radiation. ☞ Radioactive isotopes – an ☞ Faunal means - relating to the unstable form of a chemical animals of a particular region, element that release radiation as it habitat, or geological period. breaks down and becomes more stable. ☞ Refers to the use of animal bones to determine the age ☞ Isotopes – With the same of sedimentary layers and number of proton but different the materials embedded number of Neutrons ☞ Relating the succession of within those layers. events in one region to those in ☞ Share the the same chemical another requires that the two areas ☞ Scientist can determine an properties but differs in mass and be stratigraphically correlated. approximate age for a layer by therefore in physical properties ☞ Unstable Isotopes – Emits ☞ By measuring the amount of Radiations radioactive decay of a radioactive isotopes with a known half-life, ☞ C-14 – Carbon 14 (6 Protons Geologist can establish the and 8 Neutrons) Radioactive in the absolute age of the parent form of Beta Rays. material. ☞ Half – Life - The rate of decay of ☞ A number of radioactive a radioactive isotope is measured isotopes are used for this in terms of its half-life, or the purpose and depending on the amount of time required for a rate of decay, are used for material to decrease by one-half. dating different geological periods. ☞ Isotopes that decay slowly are useful for longer periods ☞ Absolute dating relies on the of time but are less accurate principles of radiometric dating, in absolute years. where scientists measure the decay of radioactive isotopes in rocks and fossils. ☞ Fossils can be dated by looking ☞ For example, in radiocarbon at the ratio of two different types of dating, the decay of carbon-14 carbon atoms. into nitrogen-14 is used to date materials that were once living, ☞ Every living thing is made of such as bones or wood. carbon, plants grab CO2 in the atmosphere and use it to form ☞ Other common methods include complex organic molecules. uranium-lead dating, potassium- argon dating, and argon-argon ☞ Animals get their carbon by dating. eating these plants. ☞ Absolute dating is a method ☞ But there are more than 1 used to determine the actual age carbon atoms. of a rock, fossil, or geologic event in years. ☞ Most carbon atoms have six protons and six neutrons we call ☞ Isotope used: Uranium-238 ☞ It is different from relative this carbon 12 which is stable. (²³⁸U) decays into Lead-206 (²⁰⁶Pb), dating, which only places events and Uranium-235 (²³⁵U) decays into or objects in sequential order ☞ High up in the atmosphere, Lead-207 (²⁰⁷Pb). without providing a specific sometimes cosmic rays hit numerical age. nitrogen atoms these creates ☞ Half-life: 4.47 billion years (²³⁸U) carbon with six protons and eight and 704 million years (²³⁵U). neutrons we call this carbon – 14 which is unstable. ☞ Uses: Best for dating rocks over a million years old. ☞ So once an animal dies the ☞ Until the advent of radiometric Carbon – 14 in its body will start to ☞ Application: Zircon crystals in dating, there was no independent go away every 5,730 years on way to test the accuracy of relative igneous rocks. dating of sedimentary sequence. average about have of the Carbon – 14 atoms will decay into nitrogen this is its half-life. ☞ With the discovery of radioactive in the late 1800’s, scientist were able to measure the exact age in years of different ☞ Isotope used: Potassium- 40 rocks. (⁴⁰K) decays into Argon- 40 (⁴⁰Ar). ☞ Half-life: 1.25 billion years. ☞ In fact, the general climactic system of chronological measurement that relates conditions as well as existing stratigraphy to time. ☞ Uses: Commonly used to species are used to define distinct date volcanic rocks. geologic time periods in the history of the Earth. ☞ It is used by geologist and paleontologists to describe ☞ Application: Igneous and the timing and relationship ☞ For example, a periodic warming metamorphic rocks. between events that have of the Earth during the Jurassic occurred throughout Earths and Cretaceous periods resulted History. in a profuse population of the decayed plants and animals that lived at that particular time. ☞ Geologist have divided Earths History into a series of time ☞ These organic materials built intervals. These time intervals are not equal in length like the hours in ☞ Another cool thing they have up and formed undisturbed layers. a day. Instead, the time intervals found in rocks tells us more about vary in length. the story of the historical parts of the Earth – The Fossils. ☞ They were eventually covered by ☞ This is because the GTS is younger, overlying sediments and then were compressed giving us divided using significant events in ☞ Scientist define fossils as any the history of the Earth. now fossil fuels such as coal, trace of living creatures such as petroleum and natural gas. a recognizable structure or impression of a structure of an organisms, trails or fecal remains that are embedded in very old rocks which are at least 5000 years old. ☞ There are certain fossils of animals or plants that are preserved in the rock record of the Earth that identify a particular span of geologic time or environment. ☞ They are called Marker Fossils ☞ The Boundary between the or Guide fossils or index fossils. Permian and Triassic is marked by a mass extinction in which a large percentage of Earths plant and animal species were eliminated. ☞ Geologic time is the chronology of the Earths ☞ Another boundary between the Formation, changes, development and existence. Precambrian and the Paleozoic These events are measured on a which is marked by the first geological time scale. appearance of animals with hard parts. ☞ Scientist do not measure geologic time on a clock or calendar. They use a linear timeline based on the age of rocks and their corresponding fossils as well as the change in ☞ By studying fossil record, life that occurred over millions of scientist were able to tell that the years. Earth has experienced different climates in the past. ☞ The Geological time scale is a ☞ The history of the Earth is another has been continuously developed and updated broken into a hierarchical set of over the last two centuries. divisions for describing geologic time. ☞ Since many scientist who first ☞ The Geology of deep time of assigned names to times in Earth’s History were from Europe, many of Earths has been organized into the names they used came from various units according to events towns or other local places where which took place in each period. ☞ Different spans of time on the GTS are usually delimited by changes in the compositions of strata which correspond to them, indicating major geological or paleontological event. ☞ EON - A very large division of geologic time equal to a billion years, or a very long period of time. On the time scale, the Phanerozoic Eon is the most recent eon and began more than 500 million years ago ☞ ERA - is the smaller time interval that divides an EON. The Phanerozoic is divided into three eras: Cenozoic, Mesozoic and Paleozoic. Very significant events in the earths history are used to determine the boundaries of the era. ☞ Ordering rock layers from the ☞ PERIOD - Eras are subdivided oldest to the youngest was the first into periods. The events that bound in creating the GTS. It showed the the periods are widespread in the order in which life on earth changed. extent but are not as significant as those which bound the eras. Each ☞ It also showed us how certain era has at least two periods. areas changed over time with regard to climate or type o ☞ EPOCH - Finer subdivisions of environment. However, the early time are possible, and the periods geologic time scale only showed are frequently subdivided into the order of events. epochs. Subdivision of periods into epoch can be done for the most ☞ It did not show the actual years recent portion of the geological that those events had happened. time scale. With the discovery of radioactivity scientist were able to assign ☞ This is because older rocks absolute age dates to critical have been buried deeply, intervals. intensely deformed and severely modified by long term earth ☞ The GTS is the product of many processes. years of research work, as well as a variety of dating techniques. ☞ As a result, the history contained within these rocks ☞ The Modern Geologic Time cannot be as clearly interpreted. Scale documents intervals of geologic time relative to one