Earth Systems and Resources Earth Science Concepts
Earth Science Concepts • Geologic Time Scale • Plate Tectonics • Earthquakes • Volcanism • Seasons • Solar intensity and Latitude
Geologic Time Scale • The geologic time scale is a system of chronological measurement that relates stratigraphy to time • Used by geologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history.
The clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth. • Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Paleozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. • The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.
Eons • An eon is the largest interval into which geologic time is divided. Four eons are: • Hadean Eon - oldest • Some of the samples brought back from the moon were formed during the Hadean Eon. • Archean Eon follows the Hadean. • Archean rocks are the oldest rocks we know of on the Earth. • Proterozoic Eon follows the Archean. • Phanerozoic Eon is the most recent of the four eons.
Eras • Each of the eons is subdivided into shorter time units called eras. • The Phanerozoic Eon is divided into: • Paleozoic (old life) Era. • Mesozoic (middle life) Era. • Cenozoic (recent life) Era.
PaleozoicEra – Rapid blooming of life: marine invertebrates, fishes, amphibians, and reptiles.
The Mesozoic Era saw the rise of the dinosaurs, which became the dominant vertebrates on land. Mammals first appeared during the Mesozoic Era, as did flowering plants.
Mammals dominated theCenozoic Era. Grasses evolved during the Cenozoic Era, becoming an important food for grazing mammals.
Periods • The Eras of the Phanerozoic Eon are divided into periods. • Periods defined on the basis of the fossils contained in the equivalent rocks. • Two recent divisions are the Quaternary Period and Tertiary Period
Epochs • Periods - subdivided into epochs - based on the fossil record • Tertiary Period divided into 5 epochs: • Pliocene • Miocene • Oligocene • Eocene • Paleocene • Quaternary Period divided into 2 epochs: • Holocene • Pleistocene
Relative Age • Placing geologic events in a chronological order as determined from their position • When discussing relative age, one rock is simply older or younger than another
Absolute Age • Using various methods of producing an actual age of a rock unit expressed in years. • Most useful and widely used method of determining absolute age is radiometric dating. (aka radioactive decay)
Half-Life • The amount of time required for one-half of the original parent radioactive isotope to decay to its stable daughter isotope • The amount of parent isotope will never reach zero. (This means if we graph the ratio of parent to daughter changes with age, we will obtain a decay curve, which approaches, but never intersects the horizontal axis.)
Plate Tectonics • Plate tectonics - scientific theory that describes the large-scale motions of Earth's lithosphere • continental drift - developed during the first decades of the 20th century • seafloor spreading - developed in the late 1950s and early 1960s
Plate Tectonics Because the continents are merely “passengers” on the larger plates – we no longer refer to “continental drift” but now call the process plate tectonics*. *from the Greek “tektonicos” for building or construction
Sea-Floor Spreading Harry Hess’s idea of how the mountain ranges formed on the ocean floor – however, he had no proof that this actually happened (1950’s).
Mid-Ocean Ridges World’s largest mountain ranges are found under the oceans
Plate Movement • Tectonic plates move because the Earth's lithosphere has a higher strength and lower density than the underlying asthenosphere. • Density variations in the mantle result in convection.
Lithosphere Broken up into tectonic plates - 7 or 8 major plates and many minor ones Where plates meet, relative motion determines the type of boundary: - convergent - divergent - transform Earthquakes, volcanoes, mountain-building, and ocean trenches occur along plate boundaries. Lateral relative movement of the plates typically varies from zero to 100 mm annually.
Types of Plate Boundaries Plate margins: divergent (where two plates move apart from each other); convergent (where two plates collide); and transform (where two plates slide past each other)
Tectonic Plates • Types: oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust • Along convergent boundaries - • Subduction carries plates into the mantle; the material lost = the formation of new (oceanic) crust along divergent margins by seafloor spreading • Total surface of the globe remains the same • Also referred to as the conveyor belt principle
Plate Boundaries Where the plates join, most of the world’s volcanoes, earthquakes, and major mountain belts occur.
Ocean-Continent Convergent When an oceanic plate collides with a continent, it will always be the oceanic plate that subducts. Features are similar to those of ocean-ocean margins. Volcanic arcs caused by ocean-continent convergent margins include the Cascades (the mountain range containing Mount Saint Helens) and the Andes.
Continent-Continent Divergent Active continent-continent divergent margins include the East African Rift, the Red Sea and the Rio Grande Rift. Where continental plates split apart, a continent-continent divergent margin or continental rift forms. Normal faulting because of the tensional stress will develop down-dropped rift valleys and thinner crust. Because of the thin crust, there is usually a high geothermal gradient as evidenced by hot springs and volcanic activity.
Active Continental Rifting Rio Grande Rift (New Mexico) East African Rift
Transform Margins Transform margins may also occur along continental margins, such as the San Andreas fault. The San Andreas fault is a transform margin joining the divergent margin in the Gulf of California to the convergent margin of the Cascades. To the east of the San Andreas is the North American Plate; to the west, the Pacific Plate.
Triple Junction • Triple junction - place where 3 tectonic plates meet • Roughly 50 plates on Earth with about 100 triple junctions among them • At any boundary they are either: • spreading apart (making mid-ocean ridges at spreading centers), • pushing together (making deep-sea trenches at subduction zones), or • sliding sideways (making transform faults) • A meeting of three plates - also a meeting of three boundaries, each with its own motion
EARS The East African Rift System (EARS) is one the geologic wonders of the world, a place where the earth's tectonic forces are presently trying to create new plates by splitting apart old ones.
EARS Triple Junction
Natural Geologic Hazards • Earthquakes • Volcanic Eruptions
Earthquakes • When the Earth quakes, energy stored in elastically strained rocks is suddenly released. • More energy released = stronger quake • Massive bodies of rock slip along fault surfaces deep underground. • Earthquakes - key indicators of plate motion
“Parts” of an earthquake • - focus - the point where earthquake starts to release the elastic strain of surrounding rock • - epicenter - the point on Earth’s surface that lies vertically above the focus of an earthquake • rupture front – the place where fault slippage begins at the focus and spreads across a fault surface (The rupture front travels at roughly 3 kilometers per second for earthquakes in the crust)
Earthquake “parts” Epicenter Rupture front Focus
Primary Effects • Shaking • Permanent displacement of ground
Not Designed to Withstand an Earthquake Collapse of city buildings – Armenia - December 7, 1988.
Shaking Causes Liquefaction Destruction of part of Anchorage, Alaska, caused liquefaction as a result of the earthquake of 1964.