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Earth


Geological and Biological Records

A more reliable history for a small part of the Earth can be found in Strathcona Park, Vancouver Island, Canada; or any places
Earth Rock Earth, History where sedimentary rocks, such as clays, shales, and limestones, are exposed. Figure 09-04a depicts the sequence of rocks (stratigraphy) that occurs within the park and immediately adjacent to it, including the names and ages of the natural rock layers or strata. The bottom layer (earliest) corresponds to the Devonian Period when earliest amphibians and first forests appeared about 400 million years ago. The Strathcona Park website carries all the information about the geology of the Park and more. While the events and objects listed in Figure 09-04a are related locally within the Park, the history of the Geological Periods in Figure 09-04b is supposed to be global with events re-constructed by geologists and paleontologists. Table 09-01 depicts the geological and biological events in each of the period.

Figure 09-04a Earth History, Local [view large image]

Figure 09-04b Earth History, Global [view large image]

Era Period (MYA) GEOLOGICAL EVENTS BIOLOGICAL EVENTS
    PRE-CAMBRIAN ERA  
HADEAN 4560-3800 Formation of Earth, solidification of crust, evidence of water, heavy bombardment. Prebiotic.
ARCHEAN 3800-2500 Beginning of rock record, evidence of plate tectonics, magnetic field generation. Protozoa (unicellular organism).
PROTEROZOIC 2500-540 Free oxygen in the atmosphere, glaciation, solidification of inner core. Metazoa (multicellular organism).
    PALAEOZOIC ERA (Era of Ancient Life)
CAMBRIAN 540-500 (new timescale) Deposition of Burgess Shale. Invertebrates (trilobites), corals, sea life of many types proliferating.
ORDOVICIAN 500-425 Sea covered most of the planet. Vertebrates, first fish, mass extinction§.
SILURIAN 425-408   Land plants, jawed fishes, ammonoids.
DEVONIAN 408-362   Amphibians, forests, sharks.
CARBONIFEROUS 362-290 Swamps and coal bearing rocks. Insects, ferns.
PERMIAN 290-245 Formation of Pangaea (the super-continent), desertification occurred. Reptiles, conifers.
    MESOZOIC ERA (Era of Middle Life, Age of Reptiles)
TRIASSIC 245-208   First dinosaurs.
JURASSIC 208-145 Oldest surviving ocean floor. Height of dinosaurs, early mammals and birds.
CRETACEOUS 145-65 Oil and gas deposits, broke up of Pangaea, global mountain building. End of the dinosaurs, first flowering plants.
    CENOZOIC ERA (Era of Modern Life, Age of Mammals)
TERTIARY 65-1.64 Himalayas and Alps folded. Evolutionary separation of apes and monkeys, most mammals established.
QUATERNARY 1.64-present Last ice age. Modern man.

Table 09-01 Geological Periods

Brief History of the Earth Figure 09-04c displays a brief history of the Earth pictorially with key geological and biological events. The terms in the picture are explained briefly below :

Formation of Earth and Core formation - See "Beginning".
Moon Formation - See "Moon".
Jack Hills Zirconµ - Zircons that formed around 4.4 billion years ago were found there.
Acasta Gnesis - Oldest intact crustal fragment about 4 Ga was found in Acasta River, Canada.
Late Bombardment - Period of heavy meteorites shower as witnessed by carters on the Moon.

Figure 09-04c Brief History of the Earth [view large image]

Bio-carbon from Isua - See "Origin of Life".
Apex Chert Fossils - Bacteria fossils from Apex Chert, W. Australia. See also "Life on Mars"
Cyanobacteria (Blue-green Algae) - See "Micro-organisms".
Rise in Atmospheric Oxygen - See "Materials for the Origin of Life".
Hard-shell Animals - See "Cambrian Period".
Dinosaurs - See "Triassic Period".
Humans - See "Hominid Species".
Geological Time Scale - See "Eras", also see "Table 09-01".
Ga - Billion Years ago.

There were four major glaciations over the last 600 million years.
§There were five mass extinctions over the last 500 million years.
µZircon (ZrSiO4) is a hardy mineral which can withstand geologic processes like erosion, transport, and metamorphism (change in structure by external agencies). Another 4.4 billion years old specimen was found also in Jack Hill, Western Australia in 2001. Its age has been identified by two independent methods.

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