3 cross cutting 3 cross cutting an igneous intrusion

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(3) Cross-cutting: (3) Cross-cutting: an igneous intrusion or fault that cuts through preexisting rock an igneous intrusion or fault that cuts through preexisting rock is younger is younger . . (4) Inclusion: (4) Inclusion: Any inclusion is older than the rock containing it. Any inclusion is older than the rock containing it. 4
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(5) Faunal succession: (5) Faunal succession: different animals throughout the Earth’s past occurred in a definite order. Relative dating of rock layers is made by application of all these principles (cross-cutting relationships, faunal succession, superposition.) 14. A surface of erosion between rocks that represents a gap in Earth history is called an unconformity. Unconformities provide information on geological processes that interrupt the normal sequence of deposition (weathering and erosion, crustal uplifts, etc.) 15 . Radiometric dating . Radiometric dating method determines the age of rocks by measuring the ratio of radioactive isotopes to their decay products. 16. According to most estimates, the Earth is approximately 4.5 billion years ol d. To date the age of the Earth, researchers look for uranium bearing rocks with a high percentage of lead -206 to uranium-238 . The half-life of uranium-238 is 4.5 billion years! 17. To date relatively young rocks and materials we use the decay of carbon-14 (Carbon - 14 dating). The half- life of carbon-14 is 5730 years. 18. The period is the basic unit of geological time in which a single type of rock system is formed. Two or more periods comprise a geological Era . Two or more Eras form an Eon , the largest division of geologic time. Some periods are divided into epochs. In the geologic history of the Earth, it is widely used the abbreviation Mya or Ma which means million years ago. 19. The time period of the Earth that spans from the formation of Earth of around 4500 Mya to 544 Mya is called the Precambrian which includes several eons. 20 . Organic life during the Precambrian era. First simple organisms - stromatolites have been found at 3.5 billion years. During the middle of the Precambrian era, simple organisms via photosynthesis began to supply atmosphere with free oxygen . A primitive ozone layer began to develop above the Earth’s surface and protect the Earth’s surface from harmful ultraviolet radiation. More complex, single-cell organisms such as algae and bacteria appeared 1.3-1.5 billion years ago. 21. Development of the Earth’s early oceans was likely due to volcanic outgassing in Precambrian era. 22. The Cambrian period was the beginning of three main Earth’s eras: Paleozoic, Mesozoic, and Cenozoic . The Paleozoic era (from 544 million years ago to 244 million 5
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years ago) is divided into six periods Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. 23. Evolution of organic life during Paleozoic era The Cambrian era – all major groups of marine organisms came into existence.
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  • Fall '08
  • Khankasayev
  • Plate Tectonics, Magnetic Field, deep ocean trenches, liquid outer core

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