Transcript Life in the Universe - Department of Physics and Astronomy

Phys178 2008
week 12 part-2
Lecture 5 & 6: Life as we know it
and Extreme Life
A/Prof. Quentin A Parker
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Life as we know it
Has changed a lot in 4 billion years!
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Life
Earth is a 'life planet'.
Probe anywhere on Earth and you will find life.
Organisms are everywhere on Earth:
Land, Sea and Air
The answer to what is life, however, is difficult.
We have examples of life but no clear definition…
 Let’s have a chat about `life as we know it’.
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Carbon-Based Life
A complex life form such as a
human, is assembled from a DNA
genetic blueprint.
All life on Earth stores its genetic
information in DNA or RNA
which are carbon-chain
molecules.
Carbon atoms can form long,
complex, stable chains.
These chains are capable of
extracting, storing, and using
energy.
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Fossilized Bacteria
Here is an image of
very old fossilized
bacteria.
The artist's
reconstruction
shows its segmented
structure.
This was found in
3.5 billion year old
rock!
Life started early!
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Miller Experiment
Stanley Miller conducted an experiment in which he duplicated the
early conditions on Earth.
He found, among other components, four amino acids.
Amino acids are the building blocks of life.
The atmospheric gases in his apparatus, when exposed to energy in the
form of an electric arc,
produced
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Amino Acids-life’s building blocks
Amino acids can link together to form long carbon
chains.
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Protein-like Molecules
Here we see that
single amino acids can
be assembled into long
protein-like molecules.
Also seen are
microsphere forms
with double layer
membranes similar to
cell walls.
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History of life on the Earth
Seen here is an entire
history of the Earth.
The age of humans is
the thin line on the top.
We are newcomers to
the planet.
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Extreme life on earth
 In the last few decades we have been discovering on
earth more and more extreme environments in which
life has been discovered
 Environments in which the prospects of life had been
considered highly unlikely
 But the tenacity and diversity and ubiquity of earthbased life continues to amaze
 The existence of life in even its most basic form in such
harsh environments has changed our views on the
prospects for extra terrestrial life
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In the complete blackness of deep
ocean valleys
 Life exists in abundance!
 Tube-worms, mussells, crabs, shrimps and mircobes
 No natural light
 Extreme pressures
 Extreme temperatures
 Yet life is seen to flourish
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Tube-worms around `black-smokers’
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Extreme life.. in
ICE……
 Microbial cells have been
found in ice cores from
other locations on Earth.
 The cores shown in this
image were taken from
above Antarctica's Lake
Vostok and are being
examined by researchers
from the University of
California at Berkeley and
the University of
Delaware.
 Credit: University of
Delaware
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ICE cores
 Scientists with the
Europa Focus Group
collected this ice core
from the North Slope
of Alaska.
 Studying unique
microbes in ice will
yield important clues
about how organisms
can live in bitterly cold
environments on other
planets.
 Credit: M. Pruis
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Lake Vostok – a pristine
environment
 Lake Vostok is believed
to contain water
millions of years old,
which may be the home
of ancient organisms.
 This hidden body of
freshwater is the size of
Lake Ontario and is the
largest of 70 bodies of
water first detected
under the polar icesheet in the 1970s.
 Credit: LDEO Columbia
University
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Lake Vostok
 Lake Vostok is about the size of Lake Ontario, and researchers believe
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that it remains liquid thanks to a hydrothermal vent at the lake bottom.
Its waters are believed to harbour a low concentration of bacterial life,
despite the fact that no sunlight has reached it for over a million years.
The meager ecosystem is probably nourished by hydrothermal energy
from the floor of the lake.
The accreted ice offers an unusual opportunity for researchers to study
these ancient life forms, because bacteria from many eras can be found,
each trapped in its own layer and flanked by older and younger
microbes that have been frozen in place throughout thousands of
millennia.
The microbes are of particular interest to astrobiologists, who believe
that extraterrestrial life may exist in similar locales – sequestered away
from harsh surface environments, such as in Europa’s subsurface ocean.
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New earth `bug’ discovered
deep underground…
 A bug which lives entirely on its own and survives without oxygen in complete
darkness underground has just been discovered in South Africa deep down in a
gold mine.
 Desulforudis audaxviator, or bold traveller as it is known in English, relies solely
on water, hydrogen and sulphate for its energy – NO OXYGEN!!!
 Because it survives without oxygen, it can perhaps offer clues to the possibilities
of life on other planets.
 This is the loneliest living species known to science
 The rod-shaped bacterium was found 2.8km (1.74 miles) beneath the surface of
the Earth in the Mponeng mine near Johannesburg, living in complete
isolation, total darkness and 60C (140F) heat.
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Stromatolites
 Life has been found in the most extreme conditions on Earth.
 Stromatolites are some of the most ancient fossils found and yet still exist today.
 These extremophiles can exist in environments in which 'normal' life would perish and
are conditions which exist on several planets of the solar system.
On this basis simple life may be thriving elsewhere in our own solar system.
Q: Can you think ok any likely candidates?
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Viruses
Are viruses alive?
This has been a hotly debated topic for decades
Opinions differ on whether viruses are a form of life, or organic structures that
interact with living organisms.
They have been described as "organisms at the edge of life”, since they resemble
organisms in that they possess genes and evolve by natural selection and reproduce by
creating multiple copies of themselves through self-assembly.
However, although they have genes, they do not have a cellular structure, which is
often seen as the basic unit of life.
Additionally, viruses do not have their own metabolism, and require a host cell to
make new products. They therefore cannot reproduce outside a host cell…..
 but could viruses survive in space or be seeded from space?
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Carbonaceous Chondrites
Amino acids have been found in
carbonaceous chondrite meteorites.
Amino acids and other complex
molecules are apparently common
in space……
So the question is… can simple life
be haboured by such things and can
they be used to transport life around
the cosmos?
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Some of the molecules that have been confirmed to exist
in interstellar space
Infrared spectroscopy in the 2.5-16 micron range is a principle
means by which organic compounds can be detected and
identified in space via their vibrational transitions. Ground-based,
airborne, and spaceborne IR spectral studies have already
demonstrated that a significant fraction of the carbon in the
interstellar medium (ISM) resides in the form of complex organic
molecular species.
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Meteorite ALH84001
Meteorite ALH 84001 seems to contain what is best described as fossilized
bacteria.
In what environment did these organisms thrive?
There was further evidence that these organisms lived in the rock in which they
died.
Materials which result from respiration were found around the fossils.
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Outline of what are believed to be possible
microscopic fossils of bacteria-like
organisms found in the meteorite
ALH84001.
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Stars' Life Zones
 A life zone around a star is a region where a planet could support life.
 Of course, life is defined in our limited terms.
 The sun's life zone is defined, as shown here, to include the space between
Venus and Mars.
Note the change in the extent of thrse zones as a function of stellar
spectral class (and hence temperature)
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Sensitivity versus range for radio
signals
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Sensitivity vs range for
SETI radio searches
 The diagonal lines show transmitters of different effective
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powers.
The X axis is the sensitivity of the search.
The Y axis on the right is the range in light years, and on
the left is the number of sun-like stars within this range.
The vertical line labeled SS is the typical sensitivity
achieved by a full sky search.
The vertical line labeled TS is the typical sensitivity
achieved by a targeted search such as from the Phoenix
project (Source: NASA technical report CP-2156, 1979).
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Extrasterrestrial life
 Extraterrestrial life is life originating outside of the Earth.
 It is the subject of astrobiology, and its existence remains
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hypothetical until a concrete example can be shown.
There is no current really credible evidence of extraterrestrial life
that has been widely accepted by the scientific community,
However, there are several hypotheses regarding the origin of
extraterrestrial life if it exists.
One proposes that it may have emerged, independently, in
different places in the universe.
An alternative hypothesis is panspermia, which holds that life
emerging in one location then spreads between habitable planets.
These two hypotheses are not mutually exclusive.
The study and theorization of extraterrestrial life is known as
astrobiology, exobiology or xenobiology.
Speculative forms of extraterrestrial life range from sapient or
sentient beings to life at the scale of bacteria.
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Panspermia
 One of the theories about how life on earth came in to being is
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the idea that living organisms are abundant in the cosmos and
are transported to the earth by comets and meteorites.
Some evolutionists agree with this idea but they say that this
only happened in the far past and that after that the
development of life was very gradual.
However, even now life on earth can be influenced and changed
by extraterrestrial life if we believe that extra-terrestrial bacteria
and viruses still descend on earth on a regular basis.
This theory is called Panspermia.
It is clear all the basic building blocks are already out there in the
COSMOS….
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Radio Communication
The first step in communicating with intelligent life elsewhere is to find a
common wavelength or radio channel.
This graph shows what is referred to as the 'water hole' wavelengths where at
about 30 cm wavelength, communication would be relatively noise free.
Another civilization using similar technology to our radio technology, would
know about this wavelength region.
To date, no signals have been found from extra terrestrial sources at these
wavelengths.
 It is pertinent to consider just how far our won signal will have reache dout into
space…
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Arecibo Message
 A message sent from the Arecibo radio telescope toward M13 is shown here.
 To date, no artificial signals have been detected.
 What are the chances of intelligent life existing elsewhere?
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The `WOW’ signal…..
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The WOW signal
 The Wow! signal was a strong, narrowband radio signal detected by Dr. Jerry R.
Ehman on August 15, 1977,
 This was while working on a SETI project at the Big Ear radio telescope of the
Ohio State University.
 The signal bore some of the expected traits if it was of non-terrestrial and non-
solar system origin.
 It lasted for a mere 72 seconds, but has not been detected again.
 It has been a focus for attention in the mainstream media when talking about
SETI results.
 Amazed at how closely the signal matched the expected signature of an
interstellar signal in the antenna used, Ehman circled the signal on the
computer printout and wrote the comment "Wow!" on its side. This comment
became the name of the signal.
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Source: Paraphrased text from Wikipedia
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The Galactic Habitable Zone
 An annular region of our Galaxy in which it has been
hypothesized that conditions are best suited to the development
and survival of life as we know it. The GHZ was first proposed in
1991 by Guillermo Gonzalez of Iowa State University and Donald
Brownlee and Peter Ward of Washington University, and has
subsequently been endorsed by a number of other researchers,
including Charles Lineweaver. Outside the galactic habitable
zone (GHZ), the theory goes, various factors make the existence
of complex (multicellular) life difficult if not impossible. The
current GHZ is said to extend from 7 to 9 kiloparsecs (23,000 to
29,000 light-years) from the galactic center, is widening with
time, and is composed of stars that formed between 4 and 8
billion years ago. The GHZ is analogous to the much more well
established concept of the habitable zone of a star.
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 According to the GHZ hypothesis, the width of the
GHZ is controlled by two factors. The inner (closest to
the center of the galaxy) limit is set by threats to
complex life: nearby transient sources of ionizing
radiation, including supernovae and gamma ray
bursters, and comet impacts. Such threats tend to
increase close to the galactic center. The outer limit is
imposed by galactic chemical evolution, specifically
the abundance of heavier elements, such as carbon.
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The Galactic Habitable zone
Several key factors conspire to place our solar system in the so called habitable zone
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Factors in our immediate Galactic environment
that may favour life
The metallicity of our Sun appears to be just right to support terrestrial planet formation….
•Old stars located near the center region of our galaxy, are metal-poor because they formed
from just hydrogen, helium, and lithium.
•Some of the the more massive stars complete their nuclear fusion cycles quickly and explode as
supernovas.
•The heavy elements produced from successive cycles of nuclear burning are dispersed into the
interstellar medium.
•Second generation stars are created out of these heavier elements, and each stellar explosion lead to
a greater abundance of available metals.
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The importance of metallicity
•A star of high metallicity, therefore, has material that originated from
many previous generations of stars…. including all the heavy elements
on earth that we believe a pre-requisites for life
•Our sun has an unusually high metallicity compared to other solarlike stars, and the reason for this is not yet understood
•whether this has an special bearing on the ability of earth to support
life is unclear
•It is possible that our star formed in a part of the Milky Way galaxy
that had a high abundance of metals (elements heavier than helium),
and then migrated to its present location.
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Planet formation
•Recent statistical studies on the metallicities of stars with
extrasolar planetary candidates indicate that metal-rich
stars are more likely to have planets.
•The most likely explanation is that a minimum threshold of
metals is required to form rocky terrestrial planets and the
cores of giant gaseous planets.
•Therefore, a star that forms from an interstellar cloud high in
heavy elements is more likely to form planets than a cloud
deficient in metals.
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Avoiding the spiral arms…
Avoiding spiral arms, where new stars form, prevents our solar
system from being gravitationally disrupted
Fortunately, our star orbits through the galaxy at nearly the same
rate as the spiral-arm rotation
This synchronization protects our solar system from crossing a
hazardous spiral arm too often
Avoiding spiral arms prevents our planet from encountering
supernovae and giant molecular clouds, which can perturb the
cometary bodies out of the Oort cloud leading to a higher number
of cometary showers in the inner solar system which could lead to
regular extinction level events.
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Much of our galaxy is a spinning disk.
We create a unit, 1 "galactic orbit" = 250 Million years. Earth has
circled the galaxy 18 times. The dinosaurs died out 2/5's of an orbit
ago. Fish began almost 2 orbits ago. Multicellular life, about 4.
Here are some comparisons
orbits
years
4 orbits ago 1 billion years  this is when multicelled life evolved
2 orbits ago 500 million years  Cambrian explosion
1 orbit 250 million years
3/4 orbit 188 million years
2/3 orbit 167 million years
1/2 orbit 125 million years
4/10 orbit
100 million years
1/3 orbit 83 million years
1/4 orbit 63 million years  dinosaurs on way out
1/5 orbit 50 million years
1/10 orbit25 million years
4/100 orbit 10 million years
1/100 orbit
2.5 million years  humas begin to evolve
4/1000 orbit 1 million years
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Location of our Sun in the wider
Galaxy..
Our solar system is located at a safe distance (about 8.5 kpc) from the Galactic
Centre.
This provides a safe haven from disruptive gravitational effects and harmful
radiation produced from clouds of ionized gas rapidly moving around a
supermassive black hole.
If our solar system were located close to the Galactic Center, the combined
perturbing effects from all the stars would cause a high flux of comets to rain in
from the Oort comet cloud.
The high number of cometary impacts would create regular global extinction
events that would prevent complex life from evolving on the inner terrestrial
planets over reasonable time-scales.
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The importance of radiation
If our solar system were located near the inner region of the galaxy,
the increased exposure to gamma radiation and x-rays, in addition to
cosmic rays, would be lethal to any life trying to evolve on a terrestrial
planet.
The effects of radiation would damage the protective ozone layers of
planets.
In addition, secondary particle cascades created in the planet's
atmosphere would be produced by high-energy particles.
This would, in turn, increase radiation levels at the surface of the
planet
Life as we know it could not exists
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The Drake Equation…
Is there extraterrestrial life (inc.intelligent life), on terrestrial planets around other stars?
The first scientist to tackle this idea head on was Dr. Frank Drake via the famous equation:
N = R* Fp Ne Fl Fi Fc L
where:
N is the number of detectable technologically advanced civilizations in the galaxy
R* the rate at which solar-type stars form in the galaxy. *
Fp the fraction of solar-type stars that have planets. *
Ne the number of planets per solar system suitable for life. *
Fl the fraction of those Earth-like planets on which life exists.
Fi the fraction of those life forms that are intelligent species.
Fc the fraction of species that develop technology and choose to send messages
L the lifetime of the technologically advanced civilization.
The first 3 factors, R* Fp, & Ne can be estimated by direct observation. The first using
statistical studies of star formation in the Galaxy from wide field surveys such as the
AAO/UKST H-alpha survey.
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