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TRANSCRIPT
Astrobiology
Prepared by Tereza Varnalı for SCI 102
‘ultra deep field’ view Hubble Space
Telescope nearly 10,000 galaxies
across the observable Universe.
Astrobiology tries to understand
Life in the context of the Universe
•Very difficult to define life (no natural definition ie. water-H2O)
Approach: (ask questions)
What is it made of? What does it need? What does it do?
• C N H O N P S (elements of life),Ca, Mg
• energy, water, a body based on organic C, adapatation strategies for
survival, leave offsprings, continuity, metabolism, mutation.
• Creates negative entropy, disequilibrium in atmosphere, radioisotope
fractionation 12C/13C
What are characteristics of life that we could list?
For example, life exhibits complex behaviour and often unpredictable
interactions.
Life grows and reproduces.
Life also metabolises.
However, the problem with all these characteristics individually is that many
non-biological entities exhibit these behaviours.
Salt crystals, when
exposed to the
appropriate
conditions, such as a
saturated salt
solution, can grow.
Fires, in a way, ‘metabolise’ organic
material. They burn organic C (trees)
in O2 (air) to produce waste
products, CO2 and H2O.
The chemical reaction involved in this
process is identical to respiration
used to produce energy in animals.
The only difference is that the
reaction is biochemically controlled in
life and uncontrolled in fires.
computer virus is a type of malicious
software program ("malware") that,
when executed, replicates by
reproducing itself or infecting other
computer programs .
We can develop working definitions of life that are adequate for astrobiology.
It may never be possible to find a ‘final’ definition of life.
Tree of life, showing domains of life / based on comparing sequences of rRNA
Prokaryotes
Diversity of life on modern earth
Prokaryotes / bacteria / bulk diversity
Physiological & Metabolic diversity
Allow life to inhabit every possible
place on earth
even on the floor of the ocean
around hydrothermal vents
in hot springs
in acidic / basic conditions
in Antarctica
in deserts...
all teeming with microorganisms
Another way to conceptualise the biosphere is to consider its tolerances to physical
and chemical extremes. We can view all organisms to be within an enormous
biological zoo surrounded by a fence. The fence is a set of physical and chemical
extremes beyond which life cannot adapt – a fence that separates life from death.
A simplified depiction of the biospace.
There are many more extremes that
define the limits of life than those
shown here. These limits could be
defined for survival, metabolic activity
(growth) or reproduction.
Limited by what we understand about life.
Extremophiles (from the Greek word philos or love) :These are organisms that not
merely tolerate extremes but have biochemical adaptations that require them to grow
under given extremes.
Extremotolerant organisms: These are organisms not optimally adapted to growth in
extremes, but have the capacity to grow in them.
We find that the edges of the biospace are dominated by microbes. As conditions
become more extreme it becomes difficult to modify the entire biochemistry of complex
multicellular organisms with their multiple cell type. Single-celled microbes have an
advantage to adapt.
Thermophiles: if their optimal growth range is 45 – 80 °C / hyperthermophiles if they
have an optimal growth temperature above 80 °C.
Methanopyrus kandleri (archaea) grows & reproduces at 122 o C (present upper limit),
Pyrolobus fumarii (archea) growth range 90 - 113 o C , both from black smoker.
Cold-loving microorganisms are known as ‘psychrophiles‘ or cryophiles’, with an
optimum growth temperature of less than 15 °C. The precise lower T limit is unknown;
the current limit : for reproduction is -15 ° C ; for metabolic activity is -25 °C.
Halophiles (Salt-loving organisms) need to grow in salt concentrations of 15 – 37%
NaCl.
Many record holding extremophiles are Archea, but are found in three domains of life.
Acidophiles inhabit extremes of pH usually below pH 3.
RioTinto in Spain, with a pH value around 2.
Alkaliphiles inhabit extremes of pH usually > pH 9.
Mono Lake in California, is an enclosed lake ~760,000 yrs old.
Salts accumulate within the enclosed lake and the result is a
shallow water environment with a pH of 10. The piezophilic or barophilic
microorganisms inhabit high
pressure environments.
Mariana Trench (10,900 m depth)
Organisms that are tolerant to radiation, but do not require it to grow are
radiotolerant.
Doses of 10,000 Gray (Gy) can be tolerated by the bacterium Deinococcus
radiodurans.
Chroococcidiopsis, a photosynthetic cyanobacterium / lives in rocks in
cold and hot deserts /other environments / can tolerate 15, 000 Gy .
To get some perspective, 5 Gy of equivalent ionizing radiation is sufficient to kill a human.
Another way in which life can deal with extreme conditions on a planetary surface is to
occupy habitats which provide shelter from extreme conditions such as rocks (geo-strategy).
Chroococcidiopsis and other microbes inhabit rock (porous).
Polyextremophiles: To understand limits of life truly, the polyextremophiles must be investigated.
Eukaryotic extremophiles
The smallest animals with resistance to extremes are the tardigrades (water bears ~0.5 mm) /
found throughout the world / including in polar regions, equatorial deserts and high mountains /date
back to over 500 mil.yrs ago.
Tardigrades can be heated for a few minutes to 151 °C or cooled to −200 °C. They can withstand
vacuum and more than 1,200 times atmospheric P. Some species can even withstand a pressure
of 6,000 atm, six times the pressure of water in the deepest ocean, the MarianaTrench.
Geological Time
Co-evolution of life and the planet
GOE
Glaciations
Continents /Supercontinent
Cambrian explosion
Extinctions
Our own species
It is not known when the human primate lineage first used tools. Evidence suggests that
Homo habilis used pebbles as tools ~2.3 million years ago and this marks the beginning
of the Paleolithic (The ‘Stone Age’), which ran through until the beginning of the last ice
age 10,000 years ago.
‘Archaic’ Homo sapiens, the forerunner of modern humans, is thought to have evolved
between 400,000 and 250,000 years ago and was using stone tools.
About 50,000 years ago , Homo sapiens began to engage in distinctly more complex
and modern behaviour, including cave painting, burying dead, making specialist tools
and jewellery.
detecting planets orbiting other stars / exoplanets
Ultimate aim:
evidence of life on
distant planets
Keppler Mission
Transit method
Doppler method
As with all species, humans face a number of threats. Some of these are natural
threats.
Some of these threats are:
Supervolcanoes
Asteroid and comet impacts
Disease
As a civilization emerges, extracts resources and generates waste gases from
various processes, it is likely that this activity may become extensive enough
tobe self destructive.
The discovery of the destruction of the UV-screening ozone layer (the so-called
‘ozone hole’) in the stratosphere by chlorofluorocarbons (CFCs) used in spray
cans and refrigerators, led to the internationally agreed Montreal Convention,
signed in 1987, to ban the use of these substances. Since that time,
concentrations of CFCs in the atmosphere have begun to decline.
From an astrobiological perspective, the Montreal Convention illustrates one
important point – that an intelligent species can develop a planetary-scale
awareness of its impact on the home world and implement policies to reverse the
damage. It is not the case that technological species with incredible capacity to
manipulate their environment are doomed to cause irreversible destruction to
their planet.
Unfortunately, there are many gases and waste products
that a technological civilization can produce. In our own
case, increases in the concentrations of CO2 is attributed to
the burning of fossil fuels.
increases in CO2 / enhances the greenhouse effect / melting
of ice sheets and glaciers / an increase in sea levels /
changes in the ranges of organisms as they begin to
respond to changing temperatures and atmosphere.
The effects of climate change are uncertain. However, more chaotic weather systems, water
shortages, major impacts on agricultural productivity and other knock-on effects have been
predicted.
Need to generate planetary-scale agreement on how to manage planetary atmosphere.
Humans have long had aspirations to leave the Earth /
first Yuri Gagarin (1934-1968) made the first orbit of the
Earth in the Vostok spacecraft in 1961 /
in 1969 when Neil Armstrong (1930-2012) became the
first human to step onto the surface of the Moon during
the Apollo 11 mission.
Our civilisation is a relatively recent biological phenomenon, but it yields insights into the
co-evolution of intelligence and its planetary environment.
Going further afield and establishing settlements beyond the asteroid belt requires identifying
locations that are relatively stable and free of the enormous radiation fields associated with the
giant gas planets.
In the Jovian system, Callisto has been suggested as a potential location for a station
The geological stability and relatively low radiation (compared
to the other Jovian moons) has made Callisto a suggested
target as a base and refuelling station for deep space missions
to the outer Solar System (image: NASA).
If we build a civilisation dispersed on a variety of planetary bodies, we may avoid extinction (unless
/Solar System-wide catastrophe). Other branches would provide redundancy and robustness to the
collapse (even if not extinction) of civilization in one location. If the presence in space becomes
expansive enough and its economic scale sufficiently large, it might even be possible that space
branches of humanity could help Earth civilization achieve
a faster reconstruction if disaster befell it.
This is the concept of a multiplanet species
A civilization (represented as the black lines) located on one
planet has a chance that a major catastrophe will destroy or
cripple it (A). A civilization that has independent, self-
sustaining branches in different parts of the Solar System (B)
has a chance of surviving a catastrophe that destroys or
temporarily incapacitates one of those branches.
Will we become interstellar?
Human civilization became an interstellar
spacefaring civilization in 2013.
The Voyager 1 spacecraft, launched in
1977, left the Solar System after exploring
the giant gas planets of the Solar System.
Will humans follow it to other stars?
Metabolic diversity
Geological Time
The Hadean, Archean, Proterozoic and
Phanerozoic are the four major eons.
Sometimes the Hadean, Archean and
Proterozoic are lumped together in a
supereon called the Precambrian /
88% of Earth’s history / biota exclusively
microorganisms.
Spiky distribution of molecules in biology
vs. all kinds of molecules abiotic occurance
if spiky distribution detected -> interesting to search for life