The Theories and Laws of Earth Science © Lisa Michalek Scientific Theories and Laws • Scientific Laws and Theories depend on basic elements of the scientific method, such as a hypothesis, testing, finding (or not finding) evidence, analyzing data and developing conclusions. • Eventually, other scientists must be able to duplicate the results if the experiment is destined to become the basis for a widely accepted law or theory. Scientific Theories and Laws • A Scientific Theory is a testable statement about how nature operates. • A Scientific Law can often be reduced to a mathematical statement, such as E = mc² with a certain set of conditions (like in a vacuum). The Big Bang Theory • The Big Bang Theory explains how the universe arrived at its present state. • Based on research performed by Edwin Hubble, Georges Lemaitre, Albert Einstein, and others, the big bang theory hypothesizes that the universe began almost 14 billion years ago with a massive expansion event. • At the time before the Big Bang, the universe was confined to a single point, encompassing all of the universe's matter. The expansion of the universe from the Big Bang continues today, as the universe keeps expanding outward. • In 1965, two astronomers using radio telescopes detected cosmic noise, or static, that didn't go away and was detectable throughout the universe. Hubble's Law of Cosmic Expansion • Edwin Hubble proved that there were other galaxies besides the Milky Way, he also discovered that these galaxies were zipping away from our own, a motion he called recession. • Edwin Hubble proposed Hubble's Law of Cosmic Expansion (Hubble's law). • This law established that the universe is made up of many galaxies, whose movements trace back to the big bang. Kepler's Laws of Planetary Motion • For centuries, scientists battled with one another and with religious leaders about the planets' orbits, especially about whether the planets orbited our sun. • In the 16th century, the scientist Copernicus described his controversial idea of a heliocentric solar system, where planets revolved around the sun, not the Earth. • But it would take Johannes Kepler, building on work performed by others, to establish a clear scientific foundation for the planets' movements. Kepler's Laws of Planetary Motion • Kepler's three laws of planetary motion, were formed in the early 17th century and describe how planets orbit the sun. • Kepler’s first Law, the law of orbits, states that planets orbit the sun elliptically. • Kepler’s second Law, the law of areas, states that a line connecting a planet to the sun covers an equal area over equal periods of time. In other words, if you're measuring the area created by drawing a line from the Earth to the sun and tracking the Earth's movement over a period of time, the area will be the same no matter where the Earth is in its orbit when measurements begin. Kepler's Laws of Planetary Motion • Kepler’s third Law, the law of periods, allows us to establish a relationship between a planet's orbital period and its distance from the sun. Because of this law, we know that a planet close to the sun, like Venus, has a much briefer orbital period than a distant planet, such as Neptune. Law of Gravitation • More than 300 years ago Sir Isaac Newton proposed the idea that any two objects, no matter their mass, exert gravitational force toward one another. • The benefit of the universal law of gravitation is that it allows us to calculate the gravitational pull between any two objects. • For example, this ability is useful when scientists are, planning to put a satellite in orbit or charting the course of the moon. Newton's Laws of Motion • Newton’s first of the three laws states an object in motion stays in motion unless acted upon by an outside force. For a ball rolling across the floor, that outside force could be the friction between the ball and the floor. • The second law establishes a connection between an object's mass and its acceleration. • The third law states, for every action there is an equal and opposite reaction. That is, for every force applied to an object or surface, that object pushes back with equal force. Uniformitarianism • The theory that Earth's physical structure is the result of currently existing forces that have operated uniformly (in the same way) since Earth formed about 4.5 billion years ago. • Mountains rise, valleys deepen, and sand grains collect now the same way they uplifted, eroded, and deposited over the past millions of years. Law of Original Horizontality • This idea was first written by Nicolas Steno in the 1660’s and states the fact that younger sediments overlie older sediments. • This principle states that sedimentary layers are initially deposited in water in horizontal layers due to gravity. Law of Stratigraphic Succession or Law of Superposition • The 2nd law written by Nicolas Steno states that the layer of earth sediment on the bottom is the oldest, and each layer of sediment gets younger as we reach the top. Law of Lateral Continuity • The 3rd law written by Nicolas Steno states that the horizontal strata extend laterally until they thin to zero thickness at the edge of their basin of deposition. Cross-Cutting Relationships • This law states that the earth layer being cut is older than the ‘thing’ doing the cutting, such as a magma intrusion (Dike) in the image below. • Described another way, an event that cuts across existing rock is younger than the disturbed rock. • This law was developed by Charles Lyell (1797-1875). Principle of Inclusion • This Law described by James Hutton states that fragments of rock (Rock A) that are contained (or included) within a host rock (Rock B) are older than the host rock. • The intruding rock (Rock A) must have been there first to provide the fragments. Law of Faunal Succession • In 1790, William Smith observed that fossils found in the rock layers appeared in a predictable sequence. • From this observation this law was developed and stated that fossils occur in a definite, consistent sequence in the geologic record.