Iffat Ara Sharmeen
Senior
School of Life Sciences,
Independent University, Bangladesh
July 22nd, 2017
Life: an undefined mystery
What makes an organism “alive”? How would something be
considered to have life? How could it arise in the first place? These
controversial questions have been stimulating and frustrating scientists since
ancient times. There has been no single, clear-cut definition of life yet,
perhaps because life is a process and not just a particular characteristic. Scientists
have pondered from one set of criteria to another, but none of these definitions
can be considered complete.
According to NASA, in terms of physics and chemistry, life is
a self-sustaining chemical system that can replicate itself. In terms of
biology, anything that contains life must be made of cells, must be able to
grow and maintain an internal environment inside itself, must be able to adapt
to a changing environment and respond to stimuli and also hold the capability
to procreate its own kind.
But these definitions do not seem to properly encompass all
known life on Earth. Viruses are not considered alive by many, simply because
they are not made of cells and are just molecules that can only replicate, grow
and sustain themselves inside a host cell. Viruses imply the notion that life
may have begun on Earth from interactions between self-assembling organic
molecules.
Life is estimated to have originated on Earth more than 3.5 billion
years ago, based on fossil and phylogenetic evidence. How life began remains a
question. The Miller-Urey experiment was a famous but basic experiment that
simulated the conditions on Earth at the time when life is thought to have
arisen, in an effort to spontaneously create complex biomolecules from these
conditions. The experiment was based on the hypothesis that the atmosphere on
Earth at that time contained water, methane, ammonia and hydrogen, and thunderstorms
occurred relatively often. It involved sealing these gases together and intermittently
sparking lightning in the gaseous mixture for a week. The presence of water
vapor allowed condensation to take place and the chemical reaction products to
settle into liquid, while mercuric chloride was added to prevent microbial
growth. Results showed that the chemical reactions among the gases could create
more than five different amino acids (the building blocks of proteins). Water
and formaldehyde could form ribose sugars (found in RNA), and hydrogen cyanide
and ammonia could form adenine (found in DNA). Other variants of this
experiment tried by other scientists have yielded more diverse biomolecules.
Since this experiment, many other theories have been tested
by recreating various conditions in the lab, to varying degrees of success. Several
precursors to life have been generated, but not life itself.
The planet Earth is very special because it is the only
planet known to harbor life. Scientists continue to search for signs of life
beyond Earth, Mars being the most talked-about planet in this sense. Why Mars?
Mars has seasons just like Earth, a slightly longer day and a slightly longer
year than Earth and almost a similar size. However, that’s not the main reason.
In 2013, NASA’s rover Curiosity found sulfur, nitrogen, hydrogen,
oxygen, phosphorus and carbon - some of the key chemical ingredients for life -
in the powder sample it drilled out of a sedimentary rock. Most of Mars’ water
exists as water vapor or polar ice caps. These ideas led scientists to believe
that Mars may have been habitable for life before, but this does not necessarily
mean that the planet contained life before. Scientists have also discovered
that Mars has lost its magnetic field. The ionizing radiation existing through
the planet, the dense carbon dioxide atmosphere, and surface topography of Mars
is not suitable for life.
Scientists have tried to come up with different ways to
detect life. Steven Benner, founder of The Westheimer Institute of Science and
Technology and the Foundation for Applied Molecular Evolution, currently works
for NASA’s astrobiology department to develop tests to detect life on other
planets. He conducted experiments to create DNA without a charged phosphate
backbone. Recall that DNA is a chain of nucleotides, each of which is composed
of a phosphate, a sugar, and a base. The phosphate backbone refers to the
phosphate groups of the nucleotides stacked on each other as the nucleotides
form a polymer. He observed that DNA with an uncharged backbone could not
recognize complementary sequences and could not extend or replicate. Under
normal conditions, the negative charges on DNA help to maintain its structural
integrity and allows it to be soluble in water. Benner theorized that anything
that contains life must contain a polymer with a charged backbone in order for
the life to replicate and reproduce. He developed tests to detect these charged
backbones, used in Mars to detect presence of alien life. But of course, life
might have evolved in a completely different language outside Earth, rendering
such tests based on our biology fairly useless.
Daniel Espinosa’s Life
What if Mars does contain life? What if there are life forms
that remain dormant in Mars and are waiting to come to life under the right
conditions? Would the life-form be anything like the life forms on Earth? Would
it be as intelligent as humans? Would such life-forms be potential threats to
our planet? Could we humans contain and control such life?
The horror movie Life, starring Jake Gyllenhaal, Ryan Reynolds, Hiroyuki Sanada and Rebecca
Ferguson helps the viewer explore and think through these questions. The movie
starts off with astronauts from the International Space Station receiving a soil
sample from Mars that might possibly contain extraterrestrial life. The crew
contains six members- a quarantine officer, a senior medical officer, a system
engineer, a pilot, a commander astronaut and an exobiologist. An exobiologist
is someone who studies the possibilities of life in other planets.
The biologist views the soil sample
under a microscope and identifies large single cell, inert but appearing to
contain a nucleus, cytoplasm and a thick cell wall lined with flagella like
projections. He increases the temperature surrounding the environment of the
cell to 20˚C, hoping that the organism would wake up from dormancy. It
did not, so he changes the atmosphere around the cell to less oxygen, more
carbon dioxide and adds glucose to the medium where the cell is suspended.
After quite some time, the cell moves, thus proving that the cell has come
alive. Schoolchildren across the United States name NASA’s new discovery, the alien
cell, “Calvin’”. Glucose intake by Calvin is very rapid and its structure
spreads throughout the Petri plate in 10 days. The cells begin to migrate from
one place to another as a unit. Growing electrical activity indicates the
growth of a neural network.
The exobiologist notes that each cell
in Calvin is simultaneously a muscle cell, a nerve cell and a photoreceptive
cell, thus each cell is multipotent which is unlike most multicellular
organisms. Most multicellular organisms have most of their cells terminally
differentiated into specific functions with very few stem cells after a
specific period of growth. This does not happen in Calvin’s case. Calvin begins
to rapidly interact with its environment without retreating. As the
exobiologist notes, “it’s curiosity outweighs its fear”. The exobiologist
develops an obsessive fondness towards the organism as it starts to grow into a
multicellular organism, like a parent-child relationship. He claims that this
organism can provide stem cells that can be used for further medical research
and cure incurable conditions.
A technical problem in the spaceship
in day 25 caused by the biologist causes malfunction in the bio-lab, which
scares Calvin into hibernation mode. After some time, Calvin is given mini
electric shocks and at one point he wakes up and attacks the biologist’s hand.
Calvin displays his intelligence by using the electric wand to escape from the
glass container. The crew immediately realize that Calvin is now a threat and
must be contained and killed immediately. Calvin interacts with a lab rat and
kills it by latching onto the body of the mouse and feeding off of it.
Calvin grows in size and continues to grow in size after
devouring one of the crew member’s internal organs. Things go even worse when
Calvin’s whereabouts become unknown. It quickly reappears to kill off two of
the remaining five crew members.
Calvin
After a series of catastrophes including the death of the
pilot, one of the doctors decides to lure Calvin into an escape pod and drive
away with it into deep space, while directing the other doctor on a second
escape pod to Earth (as the spacecraft is badly damaged). Unfortunately, the
escape pod containing Calvin and one of the doctors gets to Earth while the pod
without Calvin drives off into space. Calvin has reached Earth, which is
abundant of oxygen, water and nutrients and has the potential to wipe out all
animal life including humans. Hence the tagline of the movie, “we were better
off alone”.
Sharmeen is a fourth-year Biochemistry student at IUB. She loves to explore the real world and her inner self through science and logic.
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