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Our Unique Planet
* With notes provided by David McDonald-Christa McAuliffe Planetarium
http://www.d21c.com/AAALynx/CB/pl/earth.jpg
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What is the most unique
characteristic of the Earth?
• The presence and diversity of LIFE
What factors allow this diversity?
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1. Star/Solar System Birth Date
(Formed from an older solar nebula generation.)
• Very long ago planets would not contain
enough heavy elements.
• We need to have elements past the first
generation star level for living things.
(need supernova for fusion of elements
heavier than iron)
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http://www.atomicarchive.com/Fusion/Images/fusion.jpg
2. Age of our Sun
• The Sun needs to be in a stable burning
phase (main sequence) for constant
radiation and luminosity (heat and energy
source).
http://helios.augustana.edu/~lc/sunxray.gif
http://www.highwaygirl.com/hwg/images/star.jpg
http://www.pd.astro.it/education/PlanetV/planetarium/icons/EQUI.GIF
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3. Right Mass/Gravity of the Planet.
- Without the right mass/gravity, the atmosphere which
surrounds us would move into space as well as us.
- This also allowed the Iron Catastrophe to occur
which allowed the earths’ inner layers to form.
http://static.howstuffworks.com/gif/hot-air-balloon-atmosphere.jpg
http://teachertech.rice.edu/Participants/louviere/Images/profile.gif
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First – a handy definition:
HABITABLE ZONE (HZ)
The distance from the star where the average temperature
of the planet allows liquid water to exist.
http
://www.mallorcaweb.net/masm/Planetas/nuevosplanetas.jpg
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4.Right Distance From Parent Star
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Water exists in three states of matter
Too great= too cool for stable water cycle
Too close= too hot for stable water cycle
This is the main aspect of Habitable Zone
Also, most life needs 0-100 Degrees Celsius
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http://ag.arizona.edu/extension/riparian/images/ch3_hydro-cycle.jpg
5. Right Axial Tilt
• If too much greater - the surface temperature
differences would be too great. Ice and water vapor
would travel to the poles, no water anywhere else.
• If much less - the habitable zone would shrink in size
(think narrow band around equator)
• The tilt also allows the seasons to occur.
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http://www.learner.org/jnorth/images/imageshtml/earth-tilt.gif
6. Right Rotation Period
• If days (rotation period) were longer the diurnal
temperature differences would be too great (temperature
between night and day).
• If days were shorter, atmospheric wind speed would be
too great. (due to pressure differences caused by
different temperature air masses)
http://www.physicalgeography.net/fundamentals/images/heatingwind.GIF
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http://old.grotte-de-han.be/expo/effetserre.jpg
7. Right Gravitational Interaction
with the Moon
Affects climate and weather patterns due to
influencing the earth’s spin as well as reduces
the wobbling motion of the Earth. Also the moon
creates the tides. (High/Low 2 times a day)
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http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20power%20files/image002.jpg
8. Right Internal Earth Layers – Convection
currents in the outer core produce the
“Magnetic Field” surrounding the earth.
This provides protection from hard stellar
radiation (ex. Solar Wind ) for us as well
as keeping the atmosphere from being
swept away.
http://www.instituteforinquiry.org/inquiries/graphics/electrostorm.jpg
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Think About This……
• In 1999 Hubble space telescope indicated 125 billion
galaxies.
• Times that by a factor of 8 =1 trillion (1012) galaxies
• There are approximately 100 billion stars per galaxy
(1011)
• (1011) stars x (1012) galaxies = 1023 stars in the universe
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Probability
• If we consider (on average) a 1% chance of
each of the previously mentioned factors
occurring favorable to life, that is….
• One chance in 1040
• Compared to “only” 1022 stars in the Universe
• Therefore… we have a pretty unique home 
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