A dragon entangled in a viral icosahedral capsid

Life: Definitions, Origin, and Possibilities

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.

Extraterrestrial life and possibilities: The Red Planet

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”.

Some believe that the story was a bit too far-fetched as Calvin was depicted to be extremely hostile in the movie. However, Calvin was just trying to survive by feeding. To stay alive, it did what it had to do and reacted maliciously against anything that it felt threatened its survival. Did it really behave that differently from pathogenic bacteria? The movie director, Espinosa has stated, "If you look into the history of the human species and how we have encountered new territories and new peoples, we have not been open-minded and gentle." He urged self-reflection on how humans are aggressive against anything that does not conform to their will and their necessity to always control. If extraterrestrial life is far more intelligent than us will we allow them to dominate us or would we dominate them. Would we co-operate with each other? What would be the consequences? The movie portrays a negative consequence, but that may not be the case. Life on Earth shows that cooperation is at least as common as competition as a strategy for coexistence. If life from another planet entered and adapted to Earth, food chains and ecosystems, natural selection, habitability, in fact nature itself would change forever. As space continues to expand, only time will tell whether we will remain alone on Earth forever. 


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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