Geologic Time and Earth's Biological History PDF

Geologic Time and Earth’s Biological History Geologic Time and Earth’s Biological History What is the Geologic Time Scale and What does it Represent? The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation...

Geologic Time and Earth’s Biological History Geologic Time and Earth’s Biological History What is the Geologic Time Scale and What does it Represent? The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet. These divisions are called geochronologic units (geo: rock, chronology: time). Most of these life-forms are found as fossils, which are the remains or traces of an organism from the geologic past that has been preserved in sediment or rock. Without fossils, scientists may not have concluded that the earth has a history that long precedes mankind. Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale: The Geologic Time Scale is divided by the following divisions  Eons: Longest subdivision; based on the abundance of certain fossils  Eras: Next to longest subdivision; marked by major changes in the fossil record  Periods: Based on types of life existing at the time  Epochs: Shortest subdivision; marked by differences in life forms and can vary from continent to continent Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale  The Earth Through Time The Proterozoic: No life possible as the Earth initially forms 4.6 billion years ago. Simple, single-celled forms of life appear 3.8 billion years ago, becoming more complex and successful over the next 3 billion years: Prokaryotes then Eukaryotes Cyanobacteria begins producing free oxygen (photosynthesis) Land masses gather to make up a continent called “Rodinia”  The Earth Through Time Cambrian: Explosion of life All existing phyla come into being at this time Life forms in warm seas as oxygen levels rise enough to support life Dominant animals: Marine invertebrates (trilobites and brachiopods) Supercontinent Gondwana forms near the South Pole (note position of present-day Florida)  The Earth Through Time Silurian:  First land plants appears, and land animals follow  Laurentia collides with Baltica and closes Iapetus Sea.  Coral reefs expand and land plants begin to colonize barren land.  First millipede fossils and sea scorpions (Euryptides) found in this period  The Earth Through Time Permian:  Last period of the Paleozoic  Pangea forms. Reptiles spread across continents.  The Appalachians rise  90% of Earth‟s species become extinct due to volcanism in Siberia. This marks the end of trilobites, ammonoids, blastoids, and most fish.  The Earth Through Time Triassic:  First dinosaurs appear  First mammals- small rodents appear  Life and fauna re- diversify  Rocky Mountains form.  First turtle fossil from this period  Pangea breaks apart  The Earth Through Time Jurassic:  Pangea still breaking apart  Dinosaurs flourish “Golden age of dinosaurs”  First birds appear  North America continues to rotate away from Africa  The Earth Through Time Cretaceous:  T-Rex develops  First snakes and primates appear  Deciduous trees and grasses common  First flowering plants  Mass extinction marks the end of the Mesozoic Era, with the demise of dinosaurs and 25% of all marine life.  The Earth Through Time Tertiary:  First horses appear and tropical plants dominate (Paleocene)  Grasses spread and whales, rhinos, elephants and other large mammals develop. Sea level rises and limestone deposits form in S.C. (Eocene)  Dogs, cats, and apes appear (Oligocene)  Horses, mastadons, camels, and tigers roam free in S.C. (Miocene)  Hominids develop and the Grand Canyon forms (Pliocene)  The Earth Through Time Quaternary:  Modern humans develop and ice sheets are predominant- Ice age (Pleistocene)  Holocene Humans flourish (Holocene) Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale Geologic Time and Earth’s Biological History Geologic Time Scale Evolution of Living organisms Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale Due to the fact that early geologists had no way of knowing how the discoveries of the Earth were going to develop, geologist over time have put the time scale together piece by piece. Units were named as they were discovered. Sometimes unit names were borrowed from local geography, from a person, or from the type of rock that dominated the unit. Examples  Cambrian: From the Latin name for Wales. Named for exposures of strata found in a type-section in Wales by British geologist Adam Sedgwick  Devonian: Named after significant outcrops first discovered near Devonshire, England  Jurassic: Named for representative strata first seen in the Jura Mountains by German geologist Humboldt in 1795)  Cretaceous: From the Latin “creta” meaning chalk by a Belgian geologist Geologic Time and Earth’s Biological History Divisions of Geologic Time Scale  Hadean: This is the earliest time of the Earth and refers to a period of time for which we have no rock record  Archean: This corresponds to the ages of the oldest known rocks on earth.  Both Hadean and Archean with the Proterozoic Eon are called the Precambrian Eon. The remainder of geologic time, including present day, belongs to the Phanerozoic Eon.  Units making up the time scale are called geochronologic units  The actual rocks formed during those specific time intervals are called chronostratigraphic units  The actual rock record of a period is called a system, so rocks from the Cambrian Period are of the Cambrian system. Geologic Time and Earth’s Biological History Principles Behind Geologic Time Nicholas Steno, a Danish Physician (1669), described how the position of a rock layer could be used to show the relative age of the layer. He devised three main principles that underlie the interpretation of geologic time:  The principle of superposition: The layer on the bottom was deposited first and so is the oldest  The principle of horizontality: All rock layers were originally deposited horizontally  The principle of original lateral continuity: Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer Geologic Time and Earth’s Biological History Principles Behind Geologic Time These important principles have formed the framework for the geologic area of stratigraphy, which is the study of layered rock (strata) Younger Geologist studying the stratigraphy in the Copper Basin, Idaho. These rock layers were deposited horizontally and uplifted later so Older they are now tilted at an angle (along the red arrow). Decades later, other European scientists rediscovered „Steno’s Laws‟ and began applying them. Abraham Gottlob Werner became famous for his proposal that all rocks came from the ocean environment. He and his followers were called “Neptunists.” An opposing view by Voisins, who argued that all rocks of earth came from volcanic environments. These scientist were called “Platonists” Geologic Time and Earth’s Biological History Principles Behind Geologic Time James Hutton (1726-1797), a Scottish Physician and Geologist, thought the surface of the earth was an ever-changing environment and “the past history of our globe must be explained by what can be seen to be happening now.” This theory was called “uniformitarianism,” which was later catch- phrased as “the present is the key to the past.” William Smith (1769-1839) was a surveyor and in-charge of mapping a large part of England. He was the first to understand that certain rock units could be identified by the particular assemblages of fossils they contained. Using this information, he was able to correlate strata with the same fossils for many miles, giving rise to the Principle of Biologic Succession. Geologic Time and Earth’s Biological History Principles Behind Geologic Time The principle of Biologic Succession: Each age in the earth‟s history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species. Even though these two outcrops Rock Outcrop 1 are separated by a large distance, the same rock layer can be correlated with the other because of the presence of the same shark teeth. This lets scientists know that the two layer were Rock Outcrop 2 deposited at the same time, even if the surrounding rocks look 300 km dissimilar from each other. Geologic Time and Earth’s Biological History Principles Behind Geologic Time During the early 1800‟s, English Geologist, Charles Lyell (1797–1875) published a book called “Principles of Geology,” which became a very important volume in Great Britain. It included all of Hutton‟s ideas, and presented his own contemporary ideas such as: The principle of cross-cutting relationships: A rock feature that cuts across another feature must be younger than the rock that it cuts. Inclusion principle: Small fragments of one type of rock but embedded in a second type of rock must have formed first and were included when the second rock was forming. Geologic Time and Earth’s Biological History Principles Behind Geologic Time Charles Darwin (1809-1882) realized two major points. In spite of all species reproducing, no one species had overwhelmed the earth. He concluded that not all individuals produced in a generation survive. He also found that individuals of the same kind differ from one another. He also concluded that those with the most favorable variations would have the best chance of surviving to create the next generation The theory of natural selection was credited to Darwin (along with Alfred Russel Wallace) and he went on to write the famous “On the Origin of Species” Darwin‟s two goals in that work were:  To convince the world that evolution had occurred, and organisms had changed over geologic time  The mechanism for this evolution was natural selection