Chapter 2 Earth as a System 2.1 Earth: A Unique Planet EARTH & SPACE SCIENCE Chapter 2 Earth as a System 2.1 Earth: A Unique Planet

2.1 Earth: A Unique Planet Objectives Describe the size and shape of Earth. Describe the compositional and structural layers of Earth’s interior. Identify the possible source of Earth’s magnetic field. Summarize Newton’s laws of gravitation.

Introduction Earth, the third planet from the Sun, is the only planet to have liquid water on the surface and posses an atmosphere with a large percentage of oxygen. Earth is the only planet known to support life. Scientists study the Earth so that they can better understand the conditions necessary for life and look for those conditions elsewhere in the universe.

Earth Basics Our 4.6 billion year old planet is mostly rock, but about 70% of its surface is covered by a global ocean. Earth is an oblate spheroid, meaning that it is slighlty wider at the equator and slightly compressed from pole to pole.

Earth Basics The oblate spheroid shape is due to Earth spinning on its axis. Pole-to-pole circumference = 40,007 km Equatorial circumference = 40,074 km The difference in elevation of the highest mountain down to the deepest ocean trench is only about 20 km. Earth’s average diameter is about 12, 756 km.

Earth’s Interior Since direct observation of Earth structure is limited to the upper few kilometers, indirect methods are needed for greater depths. The study of seismic waves (vibrations that travel through Earth) has helped scientists to identify three major compositional zones and five major structural zones.

Earth’s Interior Compositional Zones Structural Zones Crust Mantle Core Structural Zones Lithosphere Asthenosphere Mesosphere Outer core Inner core

Earth’s Interior The crust is the solid, thin, outermost layer of Earth and only makes up about 1% of the mass of Earth. Oceanic crust is only 5 to 10 km thick and lies beneath the ocean. Continental crust, less dense than oceanic crust, varies from 15 to 80 km thick. The lower boundary of the crust is called the Mohorovičić discontinuity (or Moho).

Earth’s Interior The mantle, denser than the crust, is nearly 2,900 km thick and makes up about two-thirds of Earth’s mass. The core has a radius of about 3,500 km and is composed of mostly nickel and iron. The cool, brittle part of the uppermost mantle and crust make up the lithosphere that can be between 15 and 300 km thick. The asthenosphere, which is about 200 km thick, has the ability to flow (plasticity). The solid mantle rock between the core and the asthenosphere is called the mesosphere.

Earth’s Interior The depth of the boundary between the mantle and the outer core is about 2,900 km. The outer core (from 2,900 km to 5,150 km) is thought to be liquid. The inner core is presumed to be a dense, rigid solid. Collectively, the core makes up about one-third of the Earth’s mass.

Earth as a Magnet The magnetosphere is the region affected by the Earth’s magnetic lines of force that extend from the south geomagnetic pole to the north geomagnetic pole. It is thought that motions in the liquid core generate the currents that produce the Earth’s magnetic field. The sun and the moon also have magnetic fields, which does not support the idea that the Earth’s magnetic field is generated by the motion of the nickel-iron outer liquid core movement.

Earth’s Gravity Gravity is the force of attraction that exists between all matter in the universe. Newton’s law of gravitation states that the force of attraction between any two objects depends on the mass of the objects and the distance between the objects. The more massive the objects and the closer the objects, the greater the force of attraction. Objects are pulled toward the center of the Earth due to Earth’s gravitational force.

Earth’s Gravity Mass is the amount of matter that makes up an object. Weight is a measurement of the force of gravity exerted on an object. The newton (N) is the SI unit of measurement for weight (1 kg on Earth is about 10 N). An object’s weight depend on its mass and its distance from the center of Earth. Your weight at the equator would be about 0.3% less than your weight at the North Pole.

References Earth - http://www.calpoly.edu/~rechols/F03astrox103lab1.html Earth’s Compositional Zones - http://nsm1.nsm.iup.edu/hovan/classes/geos103_outline.html Earth’s Structural Zones - http://www.astro.virginia.edu/class/oconnell/astr121/im?C=D%3BO=A Mohorovičić Discontinuity - http://pbisotopes.ess.sunysb.edu/classes/oldclasses/Geo310/9-28/mohorovicic_discontinuity.htm

References Andrija Mohorovičić - http://mahazu.hazu.hr/ENG/ind-eng.html Earth’s Magnetic Field - http://www.calstatela.edu/faculty/acolvil/plates.html Law of Universal Gravitation - http://www.csulb.edu/~rtoossi/engr370i/2.htm Effect of Mass and Distance on Gravity - http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l3c.html