4. Third rock from the Sun - restless Earth

    • Seismic waves generated by earthquakes have been used to look inside the Earth, determining its internal structure.

    • There is a crystalline globe of solid iron at the center of the Earth that spins faster than the rest of the planet. This inner solid core is suspended in a much larger, fluid outer core of molten iron, which is itself encased in a thick mantle of solid rock.

    • The continents disperse and then reassemble, over and over again, roaming and wandering about the planet in an endless journey with no final destination.

    • Sound waves and gravitational data have been used to effectively empty the Earth’s oceans and see their floors, revealing an underwater range of active volcanoes that snakes its way around the middle of the ocean floor.

    • The bottom of the oceans remains in eternal youth as new floor spills out of mid-ocean volcanoes and old floor is pushed back inside the Earth, but the water above the floors has remained for billions of years, shifting about the globe as new oceans open up and old ones close.

    • The outer part of the Earth is broken into a mosaic of large plates, like the cracked pieces of an egg shell; these plates move across the Earth at the rate of a few centimeters per year, or about as fast as your fingernails grow.

    • Wheeling, churning motions deep inside the Earth's hot interior move continents sideways all across the planet.

    • The Earth's moving plates squeeze oceans out of existence, grind against each other to create earthquakes, and dive into the Earth to produce volcanoes that make continents grow at their edges.

    • Boston and Italy were once part of Africa, a glacier of ice once covered the Sahara Desert, and the Pacific Ocean once washed against the shores of Colorado.

    • A colossal alp can erode away into a small, round knob of a hill in just a few hundred million years, while continents can also weld together to form new mountain ranges.

    • The Earth’s upper atmosphere is heated and ionized by the Sun’s variable X-ray and extreme ultraviolet radiation.

    • Ultraviolet radiation from the Sun creates the protective ozone layer in the stratosphere of the Earth’s atmosphere.

    • Synthetic chemicals called chloroflurocarbons, abbreviated CFCs, have been destroying the thin layer of ozone that protects human beings from dangerous solar ultraviolet radiation. The production of these ozone-destroying chemicals was outlawed in 1987 by an international agreement named the Montreal Protocol.

    • Invisible gases help to warm the Earth by trapping the Sun’s heat and preventing some of it from being reflected back into space. This process is commonly known as the greenhouse effect.

    • Warming of the Earth’s surface and lower atmosphere by the greenhouse effect keeps the Earth from becoming a frozen ball of ice.

    • Carbon dioxide and other heat-trapping gases, such as methane and nitrous oxide, have been increasing in the Earth’s atmosphere for more than a century as the result of human activity.

    • By burning coal and oil, humans have increased the amount of carbon dioxide in the Earth’s atmosphere by 30 percent since the industrial revolution.

    • Rising seas, retreating glaciers, melting ice caps, and increasing sea and air temperatures are all recent signs of global warming from human emissions of heat-trapping gases.

    • If current emissions of carbon dioxide and other greenhouse gases go unchecked over the next 100 years, global warming could produce agricultural disaster in the world’s poorest countries, rising seas with coastal flooding throughout the world, and the spread of diseases carried by mosquitoes.

    • An international agreement to limit the human emission of heat-trapping gases was made in December 1997. Known as the Kyoto Protocol, it has had a limited effect on curbing global warming because it has not been ratified by China or the United States, two of the main climate-altering polluters.

    • The world’s most influential science academies have warned national leaders that global warming from human emissions of carbon dioxide and other heat-trapping gases poses a clear and increasing threat.

    • The 2007 Nobel Peace Prize was awarded to an Intergovernmental Panel on Climate Change and to Albert Gore Jr. for their contributions to knowledge about man-made climate change and for laying foundations to measures needed to counteract the change.

    • The Copenhagen Summit in December 2009 attempted to seek international consensus on ways to combat global warming, but it did not result in any legally binding treaty on limiting carbon dioxide emissions. Both China and the United States refused to accept such mandatory limits, but agreed with a hypothetical climate-change accord that has voluntary curbs and varying emission reductions for different countries.

    • The major ice ages, which repeat every one hundred thousand years, are caused by astronomical rhythms that alter the angles and distances from which sunlight strikes the Earth.

    • The Sun is slowly getting brighter as time goes on. It will become hot enough in three billion years to boil the Earth’s oceans away, and four billion years thereafter, our star will balloon into a giant star, engulfing the planet Mercury and becoming hot enough to melt the Earth’s surface.

    • Space weather refers to conditions on the Sun and in the Sun’s winds, the Earth’s magnetosphere, and the Earth’s outer atmosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can affect human life and health.

    • Explosive outbursts of solar flares and coronal mass ejections from the Sun can cripple spacecraft and seriously endanger unprotected astronauts that venture into outer space. Sun storms can also disrupt global radio communications and disable satellites used for navigation, military reconnaissance or surveillance, and communication, from cell phones to pagers, with considerable economic, safety and security consequences.

    • Solar proton events are the most energetic and therefore the most dangerous solar energetic particles. They can severely affect the health of unprotected astronauts traveling outside the Earth’s magnetosphere, and they are capable of penetrating spacecraft to damage or disrupt sensitive technical systems. The strongest events produce radiation doses that might be lethal to astronauts fixing a spacecraft in outer space or taking a walk on the Moon or Mars.

    • Interplanetary magnetic clouds travel behind interplanetary shocks, which are driven by coronal mass ejections. Such a magnetic cloud contains a well-organized, twisted magnetic flux tube, which can provide a “highway” for the transport of solar energetic particles.

    • When encountering Earth with the right magnetic alignment, coronal mass ejections can trigger intense geomagnetic storms, accompanied by exceptionally bright aurora, and compress the magnetosphere, exposing geosynchronous satellites to the full force of the solar wind.

    • Solar X-rays and extreme-ultraviolet radiation both produce and significantly alter the Earth’s ionosphere. The solar X-rays fluctuate in intensity by two orders of magnitude, or a factor of one hundred, during the Sun’s 11-year magnetic activity cycle. Near activity maximum greater amounts of X-rays produce increased ionization, greater heat, and expansion of the Earth’s upper atmosphere, altering satellite orbits and disrupting communications.

Copyright 2010, Professor Kenneth R. Lang, Tufts University