Tidal Theory

By: Jackelyn DiazBSEd-Bio. Sci.II

Tidal theory-- a theory of the evolution of a celestial body that is based on the action of tidal forces; specify : such a theory explaining the moon's evolution.

It is the application of continuum mechanics to interpret and predict the tidal deformations of planetary and satellite bodies and their atmospheres and oceans, under the gravitational loading of another astronomical body or bodies. It commonly refers to the fluid dynamic motions for the Earth's oceans.

Tides—motion caused by the gravitational attraction between the earth, moon and sun.

Newton (Theory of Gravity)—tides are caused by a differential gravitational pull.

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Spring tides—sun, moon and earth are all aligned. The tides are high. It occurs twice a month during full moon and new moon.

♥The gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low.

Neap tides—moon and sun are at right angles to each other. Tidal extremes are reduced. It occurs during 1st and 3rd quarter of the moon.

Absolute and Relati

ve Dating

Relative Dating—It is the science determining the relative order of past events, without necessarily determining their absolute age.

♦It is when you know the age of a certain rock layer is by comparing the fossils.

♦It can only determine the sequential order in which a series of events occurred, not when they occur.

• Superposition: The most basic concept used in relative dating is the law of superposition. Simply stated, each bed in a sequence of sedimentary rocks (or layered volcanic rocks) is younger than the bed below it and older than the bed above it. This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.

• Faunal Succession: Similar to the law of superposition is the law of faunal succession, which states that groups of fossil animals and plants occur throughout the geologic record in a distinct and identifiable order. Following this law, sedimentary rocks can be "dated" by their characteristic fossil content. Particularly useful are index fossils, geographically widespread fossils that evolved rapidly through time.

Crosscutting Relationships: Relative ages of rocks and events may also be determined using the law of crosscutting relationships, which states that geologic features such as igneous intrusions or faults are younger than the units they cut across.

Inclusions: Inclusions, which are fragments of older rock within a younger igneous rock or coarse-grained sedimentary rock, also facilitate relative dating. Inclusions are useful at contacts with igneous rock bodies where magma moving upward through the crust has dislodged and engulfed pieces of the older surrounding rock.

Determining Relative Age• Extrusion—it’s a lava hardens on

the surface . It’s younger than the rocks below it.

• Intrusion—magma cools and hardens into a mass of igneous rock. It is always younger than the rock layers around and beneath or it can be determined that the igneous intrusion is younger than the sedimentary rock.

Absolute dating is the process of determining a

specific date for an archaeological or

paleontological site or artifact or knowing exactly how old a

rock layer is.

♥Absolute dates do not necessarily tell us when a particular cultural event

happened, but when taken as part of the overall

archaeological record they are invaluable in constructing a more specific sequence of

events.

Determine the Absolute Age

Potassium-Argon Dating-- Potassium is common in rocks and minerals Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated.

Carbon-14 Dating--Sediments less than about 50,000 years old that contain organic material can be dated based on the radioactive decay of the isotope Carbon 14.

For example, shells, wood, and other material found in the shoreline deposits of Utah's prehistoric Lake Bonneville have yielded absolute dates using this method.

William Smith

• discovered regular order of occurrence of fossils in rock layers. While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers.

• As he continued his job as a surveyor, he found the same patterns across England.

• He also found that certain animals were in only certain layers and that they were in the same layers all across England.

• Due to that discovery, Smith was able to recognize the order that the rocks were formed.

• Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.

Planetesimal Hypothesis

• Planetesimal—any of innumerable small bodies of accreted gas and dust thought to have orbited the Sun during the formation of the planets. These are solid objects thought to exist in protoplanetary disks and in debris disks.

• Planetesimal hypothesis—hypothesis that the planets and satellites of the solar system were formed by gravitational aggregation of planetesimals.

Planetesimal hypothesis

• Geologist Chamberline and astronomer Moulton in early 20th century at the University of Chicago.

• There hypothesis called for close passage of another star past our sun.

• The pull of the intruder’s gravity field presumably extracted solar gaseous materials, which 1st condensed in space to form small bodies called planetesimals.

The countless numbers of these cold asteroid like bodies tens to hundreds of kilometer in diameter aggregated to form planets. As the planets grew, their strengthening gravity fields attracted still more particles.Tertiary planets—Mercury, Venus, Earth and Mars.Jovian Planets—Jupiter,Saturn, Uranus and Neptune

•The planets evolved from a cloud of planetesimals which revolved around the sun. ♥The planetesimals, the tiny cosmic fragments collided with each other and united together to form larger bodies which became planets and satellites revolving around the sun. This idea was that of a solid origin of the earth and the other planet and satellites to start with. During the near-collision, hot gases were pulled out of both stars and the gases then condensed. 

♦the planetesimals formed within a spiral disk of dust and gas surrounding a central nucleus. ♦Their gravitational attraction eventually caused the planetesimals to coalesce into protoplanetary disks from which larger objects such as planets, asteroids, and satellites were formed, while the nucleus coalesced into the Sun.

• Viktor Safronov

—his planetary hypothesis states that planets form out of dust grains that collide and stick to form larger and larger bodies.

When the bodies reach sizes of

approximately one kilometer, then they can attract each other directly through their mutual gravity, aiding further growth into moon-sized protoplanets enormously.

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