Science - Geology

• types of rocks - sedimentary; igneous; metamorphic
• sedimentary rocks - are made from broken pieces of other rocks that are eroded in the high areas of earth and transported by wind, ice and water to lower areas where they are deposited.
• sedimentary - derived from the word sedimentation which means "settling"
• igneous rocks - are formed by cooling and crystallization of hot, molted rocks called magma; it means "formed by fire"
• metamorphic rocks - are under conditions of heat and pressure similar to the environment in which igneous rocks are formed
• Principles of Original Horizontality - when sediments are deposited, they form essentially horizontal or flat layers. A corollary of this principle is that tilted sedimentary rocks were originally horizontal and that they must have been subjected to rock deformation.
• law of superposition - new rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than those closer to the surface
• principles of lateral continuity - rock layers extends laterally and cover very broad areas, especially if they formed at the bottom of ancient seas
• Principle of unconformity - the surface of non-disposition or erosion
• types of unconformities - angular unconformity; nonconformity; disconformity; paraconformity
• Angular unconformity - attitudes of beds above and below the surface of erosion or unconformity are not the same (beds are not parallel to each other)
• Nonconformity - the layer below the erosional surface is either a metamorphic or igneous rock. The layer above the erosional surface is a sedimentary rock
• Disconformity - sedimentary rock strata above and below the surface of erosion are parallel to each other
• Paraconformity - strata or beds are parallel to each other. There is no discernable erosional surface; however, there is a gap in the ages between the rock units. Represents a period of non-disposition
• the principles of uniformities - relative dating
• Absolute Dating - with the discovery of radioactivity in the late 1800s, scientists were able to measure the absolute age or the exact age of some rocks in years; it allows scientists to assign numbers to the breaks in the geologic time scale and get an absolute age of a rock fossil
• Radiocarbon dating - this is used to find the age of once-living materials between 100 and 50,000 years old. It is usually used to determine the age of human fossils and habitation sites.
• potassium-argon dating - Potassium is common in many minerals, such as feldspar, mica, and amphibole. With its half-life, the technique is used to date rocks from 100,000 years to over billion years old. Potassium-40 decays to Argon-40 with a half-life of 1.26 billion years.
• Uranium-lead dating - Uranium-238 decays to Lead-206 with a half-life of 4.47 billion years; Uranium-235 decays to Lead-207 with a half-life of 704 million years
• Jurassic - when many dinosaurs lived
• Ordovician - earth's first green plants
• Relative Dating - used to arrange geological events and the rocks they leave behind a sequence. It is based on the principle of superposition which enables scientists to arrange geological events in order.
• Index Fossils - a fossil is a remnant impression or trace of an animal or a plant of a past geologic age that has been preserved in Earth's crust that give evidence of their presence in the geologic past.
• Fossils - are not the remains of the organism itself, they are rocks. Petrification occurs when organic matter is completely replaced by minerals and the fossil is turned to stone.
• Geological Time Scale - is a system of chronological dating that relates geological strata to time and is used by paleontologists, geologists, and other Earth scientists to describe the timing and the relationships of events that have occurred.
• Eon - is a very large division of geologic time. This covers an interval of several hundred million years. The Earth's history has been divided into 4 eons: Hadean; Archean; Proterozoic, Phanerozoic. Collectively, the first three are referred to as the Precambrian.
• Era - is a smaller interval that divides an eon. For example, the Phanerozoic eon is divided into three parts: Paleozoic (early life), Mesozoic (middle life), and Cenozoic (recent life).
• Time we live today - Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch
• Precambrian Time - name given for the first super eon in history; lasted for about seven eights of Earth's history.
• Cambrian Explosion - diversification of multicellular life
• Hadean Eon - occurred 4.6 billion to 4 billion years ago. It is named after Hades, an allusion to the probable condition during this time. During this period, the solar system was forming within a cloud of dust and gas known as the solar nebula
• Archean Eon - the continental shield rock began to form. Approx. 70% of continental landmass was formed during this time. Microfossils of this time indicate that life began in the oceans about 3.5 billion to 2.8 billion years ago.
• Proterozoic Eon - also called the cryptozoic (age of hidden life). Started plate tectonics. It is generally accepted that different types of prokaryotic organisms formed symbiotic relationship.
• Paleozoic Era - era of old life began with the Cambrian explosion and ended with the Permian extinction. During this era, invertebrate animals began to diversify in the oceans. The mass extinction during this time caused most marine invertebrates as well as amphibians to disappear.
• Mesozoic Era - was the age pf dinosaurs. Reptiles were dominant animals during this era, including the dinosaurs. During this time- the break-up of the supercontinent Pangaea happened.
• Cenozoic Era - era of modern life; began about 65 million years ago and continues to the present. The Cenozoic is called the age of mammals because the diversification and importance of mammals during this era.