Transcript The Origin and Evolution of Life on Earth

1,235 Kepler mission
planet candidates, as
shown in transit with
their parent stars
ordered by size from
top left to bottom right.
Simulated stellar disks
and the silhouettes of
transiting planets are
all shown at the same
relative scale, with
saturated star colors.
Some stars show
more than one planet
in transit.
Homework #6
Due 6:00 pm, Monday, Oct. 31
Exam #2
Wednesday, November 2
Life in the Solar System?
Essentials for life
Chemicals / Nutrients
Energy
Liquid solvent
• Chemical components of cells:
– Oxygen
– Carbon
– Nitrogen
– Hydrogen
These elements make up 96% of the mass
of living organisms on Earth.
Where can we expect to find the necessary
ingredients/chemicals for life?
• These elements are abundant in the Universe,
except in older star systems
• As long as condensation and accretion occur
during a star system’s formation, we can expect
these elements to be present
What are energy sources are available?
• Sunlight (photosynthesis)
• Consuming organic molecules (ex. eating plants)
• Chemical reactions with inorganic compounds of
iron, sulfur, or hydrogen
Sunlight?
Light is most intense
near the sun (or
another star)
Light intensity falls off
with distance from
the Sun/star, going as
1/(distance)2
Inefficient far from a
star
Where can we expect to find energy for life?
• Chemical Energy
requires a means for
chemicals to mix &
interact
• Atmospheres and/or
bodies of liquids can
provide this means
What to use as a
solvent?
Liquids exist only in specific temperature and pressure ranges.
On the surface of a planet or moon, temperature alone is
insufficient for the presence of liquids.
• On Earth, all life requires water:
 Water dissolves organic molecules so they can be
used for chemical reactions in cells
 Water transports chemicals into and out of cells
 Water is directly involved in many metabolic reactions
within cells
 On
Earth, the only other common liquid
is molten rock (too hot)!
Alternative Liquids for Life
(under 1 atmosphere pressure)
Substance
Freezing
Temperature
Boiling
Temperature
Width of Liquid
Range
0C
100 C
100 C
Ammonia (NH3)
-78 C
-33 C
45 C
Methane (CH4)
-182 C
-164 C
18 C
Ethane (C2H6)
-183 C
-89 C
94 C
Water (H2O)
Water remains liquid over broader and higher
range of temperatures
The higher temperature range for liquid water
allows faster rates of chemical reactions

On colder worlds
(e.g., Titan), other
liquids may be more
common, such as
 Ammonia
 Methane
 Ethane
NH3
CH4
C2H6
Chemical reactions
are highly
temperature
sensitive, so on
colder worlds with
other liquids,
reaction rates may
be too slow for life.
ethane/methane lakes on Titan
• Advantages of water:
1. Water remains liquid over the widest range of
temperatures
2. Water is liquid at a higher temperature than the
others. High temp makes chemical reactions
easier.
3. Water is less dense when it freezes (ice floats),
allowing life to survive in the water under the ice
4. Ice insulates the water
underneath it, making it
less likely to totally
freeze, promoting
greater climate stability
5. Water is POLAR. Many
substances can dissolve
in water, but many do
not. Cell membranes do
not dissolve in water.
Earth-like cells can only
survive in water.
 Water is the most likely candidate liquid
as a solvent in life.
 Searching for liquid water may be the
best approach to searching for life.
 We do not know if other liquids can
support life.
Time to begin the search!
Is life possible on Mercury or the
Moon ?
• Small (weak gravity)
• Airless
• Heavily cratered
• No significant tectonic activity
• No volcanic gases to form an atmosphere
• No liquids likely anywhere
Is Life Possible on Venus?
• Runaway greenhouse effect:
too hot!
• High Pressure
• Life might be possible in upper
clouds (though very acidic)
• Conditions were better in early
times when the Sun was not as
bright
Is Life Possible On Mars?
Is life possible on Mars?
Once had a thicker and
warmer atmosphere and
liquid water
Liquid water may still
exist underground
Mars: A home to life?
For a good and wide-ranging discussion of Mars, check out
www.spacetoday.org/SolSys/Mars/Mars.html
The “Canals” of Mars
• In 1877, the Italian astronomer Giovanni Schiaparelli
announced that he saw canali on Mars.
• Canali means "channels" (a natural waterway) in Italian,
but was promptly mistranslated into English as "canals"
(a constructed waterway)
The most famous
proponent of the Martian
canals was the American
Percival Lowell (18551916), who took up
astronomy after reading
Schiaparelli, and
founded an observatory
in Flagstaff, AZ to study
the canals.
Lowell reported seeing a great
many canals, intersecting at
junctions he referred to as
‘oases’.
He published 3 famous & well
read books describing the canals
and arguing for life on Mars.
• Mars (1895)
• Mars and its Canals
(1906)
• Mars as the Abode of
Life (1908)
The works of Schiaparelli & Lowell formed the basis of the
popular view of life on Mars. This was carried over into the
popular literature, e.g., War of the Worlds by H.G. Wells and
many subsequent works.
Unfortunately, Lowell was wrong.
• Very few other astronomers reported seeing these
canals.
• Those that did were inevitably using small
telescopes and/or observing under adverse
atmospheric conditions.
• Mars was is cold and has too little atmophere for
canals to work.
• Long after most astronomers ceased to believe in
canals, popular media continued to speculate
about the canals.
• Much of current knowledge stems from
robotic missions to Mars (partial list):
– Viking (1976-78): 2 landers and 2 orbiters
– Mars Pathfinder (1997): lander & rover
– Mars Global Surveyor (1997 - ): orbiter
– Mars Express (2003 - ): orbiter & lander
– Mars Explorer rovers (Jan. 2004 - ):
• Spirit
• Opportunity
– Mars Reconnaissance
Orbiter (Jan. 2007 - ):
orbiter
– Phoenix (2008): lander
– Human mission (2025)?
An overview of what we know today…
– Two major terrains
• Southern Hemisphere: Ancient, heavily
cratered highlands, ~ 4km higher than
northern hemisphere
• Northern hemisphere: younger, lightly
cratered volcanic plains
• Wide variety of surface features:
Craters, impact basins, uplifted
regions, volcanoes, mountains,
canyons, polar ice caps, river
beds, flood plains
The Tharsis Bulge is a massive uplifted region the size of North
America, right between the northern plains and southern
uplands.
The Tharsis area bulges 10 km above its surroundings and is
one of the least cratered (youngest) terrains on Mars. Surface
less than 1 Byr old.
Three of Mars’
four great
volcanoes are
located here
and the fourth,
Olympus
Mons, is offset
on its NW
slope.
• Volcanoes
Including the tallest volcano in the solar system
– Olympus Mons: 24 km tall, 500 km wide, a 6 km cliff at its base
• Cracks & Canyons
– Valles Marineris: 3000 mi long, 60 mi wide, 4 mi deep
– Origin - not running water but vertical tectonics
• The only ‘canal’of
Lowell’s to exist.
• Surface: soil, rocks
– Rocks - typically volcanic
in origin
– Red color - iron oxides
What
are
they?
• Dark streaks, everywhere! Many satellite images of
the middle latitudes of the northern & southern
hemispheres of Mars show wild patterns of crisscrossing dark streaks.
Dust devils! Those seen by Spirit & Opportunity are about
the same size as those that whip up desert dust and sand
in the southwestern United States (few hundred feet).
Dust devils are a common occurrence in dry and desert
landscapes on Earth as well as Mars. Orbital images of
Mars have detected dust devils that are up to several
kilometers (a few miles) tall.
Ice Caps
• Tiny compared
to Earth.
• They are a mix
of water ice +
frozen carbon
dioxide (“dry
ice”).
Ice caps show seasonal changes
Spring at one pole: CO2
sublimates at that pole,
thereby increasing the
local atmospheric
pressure.
Fall at opposite pole: CO2
condenses out of the
atmosphere, thereby
decreasing the local
atmospheric pressure.
North Pole
Frozen carbon
dioxide (“dry
ice” covering
frozen water
frozen water
– Windy, dusty place
 During summer, a lot of frozen CO2 in the summer hemisphere’s ice
cap sublimates, increasing the local atmospheric pressure
 CO2 freezes out of the atmosphere in the opposite pole, decreasing
atmospheric pressure there
 The change in pressure leads to strong winds blowing from one
hemisphere to the other, picking up dust as it blows
–Really COLD place!
Current Mars Atmosphere
• Predominantly CO2 (~95%)
– minor contributions from N2, Ar, H2O, O2, CO
• Global mean temperature = 220 K (brrr!!)
• Atmospheric pressure = 0.6% Earth (6 millibars)
– this means that water isn’t stable; even in places
where the temp gets greater than the freezing point
Now for the good stuff:
could Mars once have been warm and soggy?
And could Mars have/had life?
Early Mars was similar to Earth