4. Third rock from the Sun - restless Earth
- Seismic waves generated by
earthquakes have been used to look inside the Earth, determining its internal
- 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
- 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
- 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
- Ultraviolet radiation from the
Sun creates the protective ozone layer in the stratosphere of the Earth’s
- 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
- 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
- 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
- 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 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