The Nebula Theory

Formation of the Earth

Seeing that New Hampshire is located on Earth, let’s concentrate now on our planet’s development. Earth is one of the inner planets and is made up of the denser (heavier) elements that were left over after the Sun was formed. The current accepted theory for planet development is known as the Accretion Theory. To accrete is to gather together or add on to. Sometimes it is easier for some people to think of the Accretion Theory as the ‘Snowball Theory’. Smaller lumps of planet building material were gravitationally attracted to larger chunks of planet building material and they collided; much like gathering a bunch of smaller snowballs together to make a larger snowball.

Collision Course

Very early on in our Solar System’s history, there were many more planets than there are today, though they were all smaller than today’s planets. The nine planets (and their moons) are the bodies that ‘won’ the collision contest. The collisions haven’t stopped, they have just slowed down and most of the larger planet-sized chunks have been swallowed up (thank goodness, as you will see).

Meteors

Approximately ten tons of new material enter the Earth's atmosphere every day. Most of this debris is the size of a grain of sand or a small pebble and burns up harmlessly in the atmosphere. At night the debris is often visible as shooting stars. Scientists call these pieces of planet building material that burn up in our atmosphere, meteors. After they burn up on entry into the earth’s atmosphere, their dust settles on the surface of the Earth.

Leonid Meteor Showers

The Leonid Meteor Showers happen when the Earth passes through the tail of Comet Temple-Tuttle. When the Earth passes through the comet's tail, all the dust and debris of the comet burns up in our atmosphere and is visible as meteor showers in the night sky. The Comet Tempel-Tuttle has an eliptical orbit around the sun. Most of its orbit is in the outer solar system. It enters the inner solar system and passes by Earth every 33 years. The next pass-by of the comet will occur in 2033. (Click on the image for a closer look.) Picture Credit: NASA, Hubble Space Telescope

Meteorites

Sometimes larger chunks survive the burning trip through the atmosphere and hit the surface of the Earth. These are called meteorites. Fortunately, most of our planet’s surface is ocean, so meteorites tend to land harmlessly out at sea. On rare occasions, city sized chunks of rock and/or ice slam into Earth and cause massive destruction. Scientists believe a large meteorite that hit the Yucatan Peninsula in the Gulf of Mexico 65 million years ago at the end of the Cretaceous period led to the extinction of the dinosaurs. They think that when the meteorite hit the Earth, it sent huge quantities of dust, smoke and debris into the atmosphere all over the world. The dust, smoke and debris blocked the Sun for many weeks or months.  This caused temperatures to drop all over the planet, causing winter like conditions everywhere. Plants and animals that couldn't adapt to the sudden changes in light and temperature died, and animals that depended on these organisms for food, like the dinosaurs, eventually died as well.

Friction

The friction of huge impacts creates heat. The relentless pounding the early Earth took generated so much heat that it melted the entire planet into liquid rock.  Yup, the Earth was a floating ball of lava in space!

Feel the Heat

Try the simple experiment of rubbing your hands together briskly for ten to twenty seconds and feel the heat generated from this relatively miniscule amount of friction.

Forming Layers

While the Earth was molten, it separated into layers, like oil and vinegar salad dressing does when it is undisturbed. The heavier elements settled towards the center of the planet, the lighter materials floated on top         (Click on the image for a closer look.)
and those           Image Courtesy of Windows to the Universe, at:
materials whose        http://www.windows.ucar.edu/
densities lay
between these two extremes were settled between the heaviest and lightest two layers.

The core separated into a solid inner core consisting mainly of iron and nickel. The inner core is surrounded by a liquid metal outer core that generates an electrical current as the Earth rotates. This spinning electrical current is responsible for the magnetic field that surrounds our planet. This magnetic field protects us from some of the more deadly forms of solar radiation by deflecting those harmful rays towards the North and South Magnetic Poles and in doing so, create the Northern and Southern Lights.

As the bombardment of larger chunks slowed down, the exterior of the earth had a chance to cool and harden into a crust as it was exposed to the coldness of outer space (there was no atmosphere in the early part of the Earth formation).

The mantle stayed molten because the crust served as insulation retained the heat generated from radioactive materials in the Earth’s interior.

The mantle doesn’t just sit there, it is in constant roiling motion due to convection of the liquid rock. The term ‘liquid’ here is slightly misleading. A more accurate description of the consistency of the earth’s mantle just below the crust is more like that of a taffy that is sticky enough to grab a hold of the rough and uneven underside of the crust and pull the crust along with it. This constant tugging at the underside of the crust by a thick, sticky substance sometimes results in separation or rupturing of the crust which might allow for the liquid rock to ooze through to the surface. But that story belongs in the  section on Plate Tectonics.

Creation of the Moon

Fitting right in with the Accretion Theory, the Giant Impactor Theory suggests that an object the size of Mars hit the still- forming Earth 4.5 billion years ago. When this object hit, it sent large abounts of superheated       material from          (Click on the image for a closer look.)
the outer layers       Image Credit: William K. Hartmann
of both bodies into
orbit around the Earth. This molten debris formed a ring around the Earth. The debris in the ring eventually stuck together to form the Moon. Supporting evidence for this theory includes:

• a lunar orbit that is slightly tilted in respect to Earth’s equator (An Earth and Moon that developed together side by side would most likely have had the Moon orbiting right over the earth’s equator.  Actually, this would have been cool because there would have been a lunar and a solar eclipse every month!  However, due to the slight orbital tilt of the Moon, most times the Moon travels above or below the Sun as seen from Earth – so no solar eclipses, or it travels above or below Earth's shadow in space - so no lunar eclipses each month either.  As a result, eclipses only happen once in a while when the Earth, Moon and Sun line up just right, as opposed to every month.);

• the Moon is moving away from the Earth at the rate of about an inch a year. As a result, the Moon is about a yard farther away from the Earth now than when Neil Armstrong walked on its surface;