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Life in the
Universe
Homework & Quiz 10 on Friday
Reading on Oncourse – “Essay 3”
Today’s APOD
The Sun Today
This week’s reading is available from the
Resource Tool on Oncourse – Essay 3
Final Exam…
Friday, 2:45 PM, here.
2 hours
100 multiple choice questions
Comprehensive
50% on chapters 10, 11 & Essay 3
50% on material covered in the first
three exams
Review sheet on Oncourse
Today’s Topics
Origin and History
of Life on Earth
What about
elsewhere in the
Solar System?
Life may be common in the Universe
Life arose quickly
on Earth
Life utilizes
naturally
occurring
chemistry
Some
microorganisms
can live in
extreme
conditions
Beginnings of Life on Earth
For its first 500 million
years, Earth was
inhospitable to life
The era of heavy
bombardment - oceans
vaporized, killing early life
Heavy bombardment
ended about 4 billion
years ago
Life arose quickly once
conditions became
hospitable
Fossils and Geologic Time Scale
 Fossils tell us about the history of life on Earth
 Based of the layering of the rocks and fossils
Earth’s history can be divided into several distinct
intervals or geological time scales.
Fossil
Evidence of
Early Life on
Earth
Ancient bacteria left fossil rocks
called stromatolites
The amount of carbon-13 in rocks with
fossils suggests life was present 3.85
billion years ago
Mechanisms
of Life on
Earth
DNA (deoxyribonucleic acid) is the
genetic material of all life on Earth
DNA can reproduce itself - the key to
heredity
The First
Living
Organism
DNA has the same basic chemical nature
in all Earth life
All Earth organisms build proteins from
the same set of amino acids
All Earth life had a common ancestor
which arose some 3.85 billion years ago
Where Did the
First Life Come
From?
A mixture of early-Earth organic molecules plus
lightning can produce all the major molecules of
life including amino acids and DNA bases
Strands of RNA (ribonucleic acid) which
resemble single strands of DNA have been
reproduced in the laboratory
The
Panspermia
Hypothesis
The idea that life started elsewhere and then
came to the Earth (via meteor impacts) is
called panspermia
Organic molecules are found in meteorites
Some microbes can survive space for years
Cyanobacteria
and Oxygen
 Photosynthesis from single-celled cyanobacteria
produced oxygen some 3.5 billion years ago
 For more than 1 billion years, this oxygen reacted with
surface rocks and little stayed in the atmosphere
 Eventually, some 2 billion years ago, the oxygen began
to accumulate, but would not be “breathable” until just
a few hundred million years ago
The first plants
on land were
probably algae
After the heavy bombardment ended, the
common ancestor of life formed
Life rapidly grew and diversified, but remained
single cell organisms for 1 billion years.
The land was still inhospitable until the ozone
layer formed – this required atmospheric
oxygen, and the first land plants emerged
The
Cambrian
Explosion
 About 540 million years ago, tiny plants and animal
organisms changed dramatically in about 40 million
years and formed into all the basic plans (phyla) that
we find on Earth today.
 The dramatic change in the diversity of life is called
the Cambrian explosion.
 The earliest humans formed only a few million years
ago (after 99.9% of Earth’s history).
Requirements
for Life
Three basic requirements for life:
A source of nutrients
Energy to fuel the activities of life
Liquid water (the biggest constraint)
Life in
the Solar
System
Where in the Solar System can we find
the basic requirements for life?
Life on other Terrestrial Planets?
X
MERCURY
Extreme Temperatures, No Atmosphere,
UV, Cosmic Rays, No Liquids
X
Extreme Temperatures
No Atmosphere, UV, Cosmic Rays
No Liquids
X
High Temperatures
No or Little Water
Young Surface  No Fossil Record
MOON
VENUS
?
MARS
Once had Liquid Water
Ice Present Now, Temperatures OK
Too hot!
Too cold!
The
Habitable
Zone
•The planet needs to be the right
distance from the star. WHY?
•The star needs to have the right mass.
WHY?
Life on
Mars?
Rovers studied Martian conditions to
see if life might have existed
No evidence for life now
Maybe life in the past
The Martian
Meteorites
 Meteorite found in Antarctica is of Martian origin
 Inside the meteorite were complex organic materials
and structures which looked like nanobacteria
 Similar structures can be made by chemical and
geological means
 Contamination from Earth may also explain the
presence of organic materials
Life on the
Gas Giants?
 Ingredients for organic chemistry
 Atmospheric layers with temperatures like Earth
 But no solid surfaces or liquid water
 Winds and turbulence mix gas quickly over
extremes of T & P
 Sunlight is very weak, but some internal heat
 Hard to explore!
What about
the Moons of
Jupiter?
Io
Europa
Ganymede
Callisto
Io – The most volcanic object in
the Solar System
Europa – A
“cracked ice crust”
over a water ocean
Life on
Jupiter’s
Moon
Europa?
 Europa may have enough tidal heating to form a
subsurface ocean underneath its icy crust
 Life there could form like the deep sea vents on Earth
 Larger life forms could exist in the vast oceans, but
energy sources are limited and this would tend to limit
the size of any life there
Jupiter’s
Moons are
Heated by
Tides
Tidal heating occurs because
Io and Europa’s orbits are
eccentric
Enceladus
Small icy moon (500 km
diameter) of Saturn
Young, crater-free
surface regions with like
those on Europa
Orbit resonance with
Dione
South polar hot spot and
ice plumes
Thin “atmosphere” of
water vapor
Subsurface ocean!?
Titan
Moon of Saturn
The atmosphere is denser
than Earth’s but very cold
(100K) and mostly CH4 and
N2
Enshrouded in smog-like
clouds
Methane acts like water
Few craters on the
surface
Surface eroded by liquids
but no oceans
Ganymede, Callisto, and Titan
Ganymede and Callisto might have
subsurface oceans, but their internal
heat is small and liquid water would not
be terribly abundant
Titan has no native liquid water, but an
abundance of organic materials.
Could life evolve from the lakes of
methane?
Water might be brought in from comets,
but this would eventually freeze
Triton
Extremely cold (<40K)
moon of Neptune
Moons made from
volatile materials
produce icy volcanism
Huge geysers of
nitrogen!
Pluto and the Kuiper
Belt Objects may look
and act similarly.
Environments for Life
Surfaces of Planets (or Moons)
 Location, location, location…
 Size matters (for retaining an atmosphere)
 The star matters
Overall, However
 There is an incredible diversity of worlds!!!
 Warm pockets or oceans of liquids plus organics may
exist in a variety of environments outside the classic
Habitable Zone
 Even on Earth not all life requires starlight for an
energy source. Sources of potentially life-giving
energy may exist even in the cold outer reaches of
our own and other planetary systems
Is Life Rare or Common?
 Some feel that an Earth type planet (with its complex
type of life) is rare:
 Galactic constraints
 Too close to the galaxy’s center and the rate of supernovae are
too great.
 Too far from the center and “metal” content is too low.
 A stellar system needs a Jupiter-like planet to sweep-out and
deflect meteors that might wipe out life on Earth.
 Climate stability
 Plate tectonics and the carbon dioxide cycle.
 Earth’s large Moon keeps axial tilt relatively stable.
 Counterarguments to the Rare Earth Hypothesis
 The above conditions may not affect the creation and
advancement of complex life as much as we think
 There may be other overlooked conditions and processes that
could assist the creation and advancement of complex life
Or is the Universe Life-Friendly?
 Water and carbon chemistry are everywhere!
 Hydrogen, Oxygen, Carbon, Nitrogen
 1st, 3rd, 4th, and 6th most abundant elements
 Organic chemistry is found in
 Interstellar gas clouds, comets, meteorites, outer planet and
moon atmospheres
 Physical Laws
 Copasetic Time Scales
 Expansion rate of the Universe & stellar lifetimes compatible
with time to evolve complex life
 Abundant Materials
 Even small changes in physical constants would cause little
hydrogen or carbon to exist
 Huge Diversity of Environments
Dates to
Remember
 Reading, homework, quiz next week
 Last Homework, Quiz on Friday
 Final on Dec. 19 at 2:45 PM