FREE ESSAY ON FROM THE BIG BANG TO LIFE ON EARTH

FROM THE BIG BANG TO LIFE ON EARTH

From the Big Bang to Life on Earth
Should we as humans expect to find intelligent life elsewhere in the Universe? There are
many reasons for and against this concept, but first we should trace just how our
terrestrial life started.
The beginning of time and the universe began with the Big Bang. This was an explosion
that started the expansion of the universe. In the most basic sense, the standard model
is simply the idea that every bit of the matter and energy in the universe was once
compressed to an unimaginable density. In the big bang, the material exploded outward
into the formation of matter that we see today. Shortly after this event everything in
the universe was very dense and very hot. It was only until 500,000 years later that it
cooled enough so that hydrogen and helium could form by fusion processes. Even then, it
took another two billion years of cooling for enough clumps of interstellar dust and gas,
called molecular clouds, to achieve stability in the universe.
From these molecular clouds, stars were able to form due to compression of the material
by gravitational forces. In the core of a star fusion takes place that causes it to emit
light. If the star is initially large enough, its death happens in the form of a
supernova explosion. During this explosion, in less than one second, every element up to
and including uranium is synthesized by fusion and dispersed into space. As time passed
in the universe, the heavy element content as a whole increased, so new stars were more
enriched.
Production of planets is an entirely different process. Planets form from the accretion
disk surrounding newly formed stars. This material, comprised of dust and rock, collides
and sticks together eventually gaining enough mass to become a planet. This process was
responsible for the unique and very important aspects of Earth. We now focus our
attention on the formation of one particular planet, one that is so far unlike any other
in the universe, Earth.
In the beginning, impacts of very large objects were very common, some as big as Mars or
half the diameter of Earth. Collision of large bodies orbiting Earth played a role in its
initial tilt of spin axis, the length of its day, direction of spin, and the thermal
state of the interior. This violent bombardment continued for 3.9 billion years. Final
composition of Earth had several crucial structural effects. Enough metal was present
early on to allow formation of an iron and nickel rich core that is partially liquid.
This enables a magnetic field that deflects some harmful radiation from reaching the
surface. Enough radioactive elements are also present in the core to maintain long term
heating which drives plate tectonics. At 4.5 billion years ago, Earth separated into
different layers: an inner core (made of iron and nickel), a land layer of lower density
material, and an early atmosphere of carbon dioxide and steam. At 3.9 billion years ago,
surface temperatures dropped to a range where liquid water could be maintained. Liquid
water makes up approximately 75% of the planet's surface today which is roughly what it
was then. The most important requirement for life as we know it is the presence of liquid
water. This is the one substance that can serve as a universal solvent - that is, it can
dissolve and transport minerals and nutrients from both the ground and from the
atmosphere and can allow the mixing of these materials. No other substance can perform
this function that is integral to the appearance and continuation of life as we know it.
Therefore, within even our limited understanding, it seems that liquid water is essential
to the formation of life.1 A planet having water in the liquid state in conjunction with
land masses seems to be an important factor in the creation of life that is not seen on
many other worlds. The formation of land was due to volcanism and plate tectonics. Land
can remain a constant on the surface of the Earth since erosion is counteracted by new
formation of land by these two processes. 
At about 3.8 billion years ago evidence through analysis of fossils indicates the first
signs of life on the planet. There is a consensus that all life on Earth is based on the
DNA molecule. The creation of DNA involves the following: The synthesis and accumulation
of small organic molecules such as amino acids and phosphates, the joining of these small
molecules into larger ones such as amino acids and nucleic acids, the aggregation of the
proteins and nucleic acids into droplets that are chemically different than their
surrounding environment, and finally, the replicating of the larger complex molecules and
the establishment of heredity.2 Because of this daunting process, DNA has not yet been
successfully synthesized in a laboratory setting. It has been argued by some that the
first life appeared in warm ponds and by others that it first happened in deep-sea
volcanic vents. Still, others believe that life may not have even started on Earth at
all, but was seeded from another nearby planet such as Mars or Venus. In any case, life
was rooted on the planet Earth by 3.5 billion years ago. Once originated, or contaminated
from elsewhere, life evolved quite rapidly. It is hypothesized to follow this pattern:
prebiotic broth, unknown step possibly some kind of extremophile (similar to the ones
still found on Earth today in extreme heat and cold temperatures), RNA, protein
synthesis, DNA, primitive cells, bacteria, archea, and finally eukaryotes. Only the
evolution of eukaryotes is important here since it is the basic prerequisite or complex
metazoan and animal life. During a 500 million year interval from 1 billion to 550
million years ago, the change from single-celled microbes to multicellular creatures
occurred. Also during this time Earth's environment experienced significant changes such
as ice ages, rapid continental movements, and drastic changes in oceanic chemistry.
Mountains and continental drift helped shape the planet's land masses into a formation
not unlike present day. Plants were the first multicelled organisms on Earth. At about
600 million years ago, the first appearance of larger metazoans occurred after a sudden
increase in atmospheric oxygen. The element oxygen is a key to the appearance of larger
animals due to their metabolism system requiring the gas for survival. 
Could this exact process or a similar one have happened to create life on some other
world in the universe? To answer this, we must determine the guidelines for what makes a
planet suitable for the appearance and evolution of Earth-like life. 
It has been hypothesized that for a world to be capable of inducing and sustaining life
it must be located within a certain habitable zone or HZ. A habitable zone is defined as
a region where heating from the central star provides a planetary surface temperature at
which water can exist as a liquid. This distance range varies for each star-planet system
as it depends on the magnitude of a star's brightness. A larger and brighter star than
the sun would have a HZ farther away and a smaller star would have a HZ closer to it. But
there is a paradox here, if a planet forms close enough to a star to be in its habitable
zone, it typically ends up with little water and hardly any carbon compared to bodies
that form outside the HZ. 
Compared to other stars, our sun is not typical. Over 95% of all stars in the universe
are less massive than the sun. For multiple star systems, the habitable zone gets more
complicated. Two-thirds of solar type stars (M class) in our Milky Way galaxy are members
of binary or multiple star systems. When two stars are orbiting close together, their
planets orbit both stars. When the stars are far apart, their planets only orbit one of
them. Some problems with this situation include: Planets may not be able to form unless
the stars are at least 50 AU away (1 AU = distance from the Earth to the sun) and stable
orbits can only be achieved where companion stars are at less than 20 million miles apart
or farther than one billion miles.3 A planet's orbit pattern is also of concern. Earth's
orbit is very stable and only has a small degree of ellipticity. A highly elliptical
orbit would cause a planet to oscillate in and out of a habitable zone. If a planet could
even form in this situation, their orbits would be perturbed by varying gravity of more
than one star causing ejection or falling into one of the stars. Another factor in
considering the habitable zone is insolation. Insolation is the stellar energy a planet
receives. This quantity could only vary by as much as ten percent without affecting its
habitability. Much less than ten percent fluctuations on Earth is what causes our climate
changes during seasons. Furthermore, the insolation effect would be magnified in a binary
star system due to periodic eclipse of one of the stars. 
Rather than focus on individual star-planet distances in reference to their habitable
zones, let us choose the entire Milky Way as a basis. The diameter of our galaxy is about
85000 light-years across. Our sun is located 25000 light-years from the center of the
galaxy. Our solar system is located in a region where star density is low, which is
indicative of the habitable zone of the Milky Way. Places further toward the center of
the galaxy are too densely packed with stars to be in the HZ. The outer zone has a
different problem: the wrong type of matter for Earth-like planets exists there, the
concentration of heavy elements and rate of new star formation is too low. Even the shape
of the Milky Way is important. Our spiral shape is much preferred to elliptical since
elliptical galaxies typically contain no heavy elements, little dust, little new stars,
and an abundance of asteroids and comets. 
It has also been hypothesized that a habitable time zone exists for the creation of
Earth-like systems. For two billion years after the Big Bang, carbon, oxygen,
phosphorous, potassium, sodium, iron, copper, as well as uranium were not present in the
universe. These elements are required (among a few others) for organic life. Only after
this time period were supernovae explosions able to produce heavy elements up to uranium.
Stars forming now have fewer radioisotopes than the sun did when it formed 4.6 billion
years ago. If a planet were to form around a star with fewer amounts of these isotopes,
the planet's core would not have enough radioactive heat to drive plate tectonics. Also,
galaxies 30-40% older than ours seem to have more instances of being irregularly shaped,
and therefore not able to contain an Earth-like system. 
To expand the habitable zone to a broader category, consider the entire universe.
Statistically the universe is either too cold or too hot, too dense or too vacuous, too
dark or too bright, or contain too little heavy elements to support Earth-like planets.
However, even though time and statistics my prove otherwise, I adamantly disagree that
these findings lead to Earth being totally unique and the entire universe being devoid of
intelligent life. 
The vast, almost incomprehensible size of the universe leads me to believe that the
information that we know at this time is astronomically smaller than what we don't know
about its properties. For example, in 1961 there was a now renown conference held at the
National Radio Astronomy Observatory in Green Bank, West Virginia, to discuss the
question of a 'search for extraterrestrial life' (SETI). That gathering brought together
a worldwide array of prominent astronomers and exobiologists. The conference set out with
the intention of attempting to quantify, by theoretical means, the number of technically
advanced extraterrestrial intelligence civilizations within the Milky Way galaxy. The
solution was an equation, now known as the Green Bank equation, though also widely
referred to as the 'Drake equation' after Frank Drake the astronomer who proposed the
core of the expression. The equation seeks to quantify the number, N which is the number
of technical civilizations in our galaxy.4 The equation is as follows
N = R fp np fl fi fc L
where:
R = mean rate of star formation in the Milky Way
fp = the fraction of those stars which form planetary systems
np = the number of planets in those systems which are ecologically suitable for life
forms to evolve
fl = the number of those planets on which life forms do actually develop
fi = the number of those life forms which evolve to an intelligent form
fc = the number of advanced intelligent life forms which develop the capability of
interstellar radio communication
L = the lifetime of those advanced technically advanced civilizations
Values for most of these factors are far from being certain, but some have been
estimated. In fact, only the value of L has been altered to any significant degree since
the SETI conference in 1961. The estimations include:
R = 10/year
fp = 0.5
np = 2
fl = 1
fi fc = 0.01
L = 34
So even if these estimates vary, the number N of technical civilizations only present in
our galaxy equals 3.4. If technically advanced civilizations were to exist and have
lifetimes of a few thousand years then a galactic community appears a distinct
possibility. Other researchers and working groups, for example Sagan5 , have examined the
question and concluded there could be 106 technologically advanced extraterrestrial
civilizations in the galaxy. That's 106 civilizations in our relatively small galaxy
alone! Hubble's Deep Field (taken near Ursa Major in the Big Dipper constellation) has
found more than 1500 individual galaxies. For just this tiny region of space (about 2.6
(arc-min)2), N would equal 159,000 civilizations. 
In addition to these encouraging calculations, science has now proven that life could
evolve on a basis other than DNA. Furthermore, life does not have to be carbon based.
Life may be derived from other elements such as silicon. Hydro-silicon molecules are
possible, but since the silicon atom is much heavier than the carbon atom, the atomic
bonds for silicon are only stable at much lower temperatures than for carbon (on the
order of -150 F). So hydro-silicon compounds might form, for example, on the moons of the
Jovian worlds where the temperatures are low.6 
As of yet, the Earth has not experienced any contact from these other intelligent beings.
I agree that this is a fact that does not support my ideas of the existence of such
beings. However, I believe that it is possible that life as we know it may not be
advanced enough, technologically speaking, to have the ability to contact
extraterrestrials. Or, we presently may have the technology, but since humans have only
had the ability to send detectible waves (like radio) outward from the planet for the
last 100 years or so, and taking into account the great distances these waves have to
travel, it is quite possible that nothing intelligent has heard us yet. In my opinion, if
indeed we are alone in this universe, wouldn't it just be a terrible waste of space?
Bibliography
1. http://www.setileague.org/articles/little.htm
2. Ward, Peter D. and Brownlee, Donald. Rare Earth - Why Complex Life is Uncommon in the
Universe. Copernicus, 2000
3. Kuhn, Karl F. In Quest of the Universe. 2nd Edition. West Publishing Company. 1994
4. http://www.u-net.com/ph/mas/home.htm
5. Hawking, Stephen. The Big Bang and Black Holes. Vol. 8. World Scientific Publishing
Co. 1993 
6. http://www.edventure.com