Earth.pptthe be planet earth evolution 11

Presentation by: Heather DeRoy

Discovery of New Planet!
 Planet Earth, a part of a Solar System, is a possible
candidate for life

Let’s investigate whether life is
possible on this new planet,
Earth!

Let’s investigate the location of
planet Earth to see if it is a
possible location for life to
form!

Galactic Neighborhood
 Galactic environment
impacts habitability
 Milky Way galaxy’s edge is
a life-favorable spot
 Not near active gamma
ray source
 Not near galactic center
with high star density
and ionizing radiation
 Loneliness in galaxy is
helpful for life

The galactic neighborhood is
good… let’s investigate the star
it orbits!

Spectral Class of Star Needed for
Life:
 Spectral class indicates
photospheric temperature
 “HabStars” spectral range
 Early F
 G
 Mid-K
 7000K to 4000K
 Emit high-frequency UV radiation
to trigger atmospheric ozone
formation
 Emits not so much that ionization
destroys life

Spectral Class of “Sun”
 Earth rotates around the star, the “Sun”
 Sun
 G2 star
 ~6,000K
 Sun is in “Habstar” range!
 Ozone can form in atmosphere
 Ionization is not deadly for life

Low Stellar Variation?
 All stars change luminosity
 Stars vary in stability… stars that
fluctuate luminosity violently are
poor candidates for hosting life
 The Sun is relatively stable!
 Solar variation is ~.1% over 11-
year cycle
 Slight variations dramatically
impact Earth
 Little Ice Age – decline in Sun’s
luminosity

Now that we know the Sun star
is a good candidate to support
life, let’s look at planet Earth’s
position relative to the Sun!

Habitable Zone
 Theoretical shell around a star
where any planet present would
have liquid water on its surface
 HZ range should not vary over time
 Stars increase luminosity as
they age
 If this happens too quickly
(super-massive star), planets
are only in window for life for
short amount of time
 Lowers time to develop life

Is Earth Located in Habitable Zone?
 Yes!
 Earth is located within the expected shell of distance
in which liquid water can be on the surface of the
planet!
 Pictures of the planet show liquid water covering a
large portion of the Earth’s surface!

The relative position of Earth
appears capable of supporting
life… so let’s look at the planet
itself!

Planet Characteristics that Support
Life
 Terrestrial
 Silicate rocks
 Rocks not accreted to
gaseous outer layers
 Gas Giants = no life
 No surface
 Enormous Gravity
 Satellites are good
candidates, however

Composition of Earth?
 Earth is a terrestrial planet, not a gas giant

Mass of Planets need to be Just
Right for Life
 Low Mass
 Bad news for life
 Lesser gravity – difficult for atmosphere retention
 Smaller planets lose energy from formation quickly
geologically dead
 Approximately 0.3 Earth masses needed to sustain life

Mass of Earth
 High Mass
 Earth is largest by mass and density of terrestrial bodies in the
Solar System
 Large enough for molten core (heat engine)
 Large enough for atmosphere through gravity
 Large enough for liquid outer core and metal inner core
(magnetic field)

Magnetic Fields and Life
 Planets need protection from solar wind
 Solar wind- stream of charged particles from stars
consisting of electrons and protons
 Planet must have molten metal interior

Does Earth have a Magnetic Field?
 Yes!
 Earth has solid metal core with liquid outer core,
causing magnetic field
 Protects the Earth from solar wind

Atmosphere and Life
 Atmosphere – layer of gases that surround a material
body of sufficient mass
 Held by gravity
 Helps regulate temperature
 Protects planet from meteors and radiation
 Composition favors life (oxygen and carbon dioxide)

Does Earth have an Atmosphere?
 Yes!
 Earth’s atmosphere is made up of
 Nitrogen (78%)
 Oxygen (20.9%)
 Argon (.93%)
 Carbon Dioxide (.0390%)
 This composition could support life
 Atmosphere absorbs/reflects
harmful radiation
 Visible and Radio reach surface

Composition of Planets
 Four elements vital for life
 Carbon
 Hydrogen
 Oxygen
 Nitrogen

Earth’s Composition?
 Element oxygen alone found in Earth’s crust…
 However, other life elements are found in atmosphere
and water
 Make amino acids (building blocks of protein)
 Comets and outgassing from volcanoes brought these
elements

Tectonic Activity of Planet
 Supply surface with life-sustaining material
 Supply atmosphere with temperature moderators
(CO2)
 Recycles important chemicals/materials
 Helps increase environmental complexity
 Earth is tectonically active!!

The planet Earth itself looks
hopeful for supporting life…
what about it’s orbit and
rotation?

Life-Supporting Orbits
 Stability is critical
 Eccentricity
 Greater e, greater temperature fluctuation
 Living organisms can only withstand certain fluctuations
 Complex organisms have greater temperature sensitivity

Is Earth’s Orbit Suitable?
 Yes!
 Earth’s Orbit
 Almost circular
 E < .02

Life-Supporting Rotation
 Rotation around axis at tilt
 Planet should have moderate seasons or
biospheric dynamism will disappear
 Without tilt, planet would be colder (warm
weather could not move poleward)
 Should not be radically tilted because seasons
would be extreme
 Speed of Rotation
 Should be relatively quick so day-night cycle is
not too long (temperature differences if long
days/nights)

Earth’s Rotation?
 Earth’s tilt varies between 21.5 and 24.5 degrees every
41,000 years
 Day is only 24 hours
 Moon plays crucial role
 Moderates Earth’s climate by stabilizing axial tilt

Earth COULD have life!
 Galactic Neighborhood
 Arm of Milky Way galaxy
 Star
 Spectral class G2
 Low stellar variation
 Distance from Star
 Earth is located in Habitable Zone
 Liquid Water
 Composition/Size
 Terrestrial planet, relative high mass
 Magnetic Field
 Atmosphere
 Orbit
 Nearly circular
 Rotation
 Tilt allows seasons
 Short night/day

Earth.pptthe be planet earth evolution 11

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