The Origin of Life Lead: Thomas Davis

2/5/2008

Summary by Alexander Joy

Life as We Know It and Its Evolution

The session on February fifth discussed the origins of life in the universe. The progression of life can only be fathomed within the limited scope of human knowledge: we know only of life on our planet, of our elemental composition, and from what genetic records we have in the present day. Using a combination of astronomical backdating and charting evolutionary progression, we are able to take the information from today's age and work backwards. From the data unearthed during this backwards progression, we can draw closer to answering the biggest questions concerning the origin of life: the how, and the when. The “why” query lies outside the scope of scientific inquiry, but the session decided to address the issue at a later time.

For the purposes of the discussion, life was bifurcated into two distinct categories: life as a property, and life as a category. Life as a property encompasses all the different aspects required for an organism to be classified as “living.” The session addressed the properties of reproduction, cellular composition, metabolism of energy (including anabolism and catabolism), and the presence of a genetic system; furthermore, these properties were deemed the prerequisites of life. As a category, life simply differentiates the living from the nonliving. While it can be said that any particular entity has the property of life, the distinct dichotomy between the living and the nonliving separates the two into different categories.

An approximate timeline of the cosmos was examined to facilitate the first moments of the session, in order for the ensuing discussion to have a common foundation that all the participants could use. Studies suggest that the Big Bang, the enormous condensation and explosion of particles and gravity that gave rise to the universe, occurred around 13.7 billion years ago. Later on, the stars arose from the remnants of the Big Bang. It is speculated that the first stars appeared nearly 12.7 billion years ago. The next salient date (for discussion purposes) was 4.5 billion years prior to the present, when a primitive earth was first formed. Fossil evidence indicates that the first life on earth surfaced 3.6 to 3.8 billion years ago, as basic prokaryotic cells (ancestral cells that bear a resemblance to the bacteria of the present). Later on, the aforementioned cells evolved into more advanced eukaryotic organisms, from whence other species eventually emerged.

Even though we can deduce when the first life on earth came into being, we do not yet know how it appeared. Several theories were examined in the session. One perception is that life itself is not of earthly origin, and that all life is a product of simple single-celled organisms from another place in the universe. Should this be the case, it is hypothesized that the first life would have been bacteria transported to earth via a meteorite. The theory is dubbed panspermia, from the Greek prefix meaning all. Another theory is that life spontaneously arose as a result of the mix of molecules adrift in earth's primordial waters – a soup of elements that formed due to earth's comparatively cool temperatures. Further difficulties concerning the advent of life arise when the system of DNA is examined. All of the proteins found within cells are the products of genes, which are located inside DNA. All living cells encode and interpret DNA, using it as a “blueprint” to develop specific proteins (and, consequently, variety of structure). However, we know of no origin for cellular proteins other than previous cellular proteins. This creates a scenario comparable to the age-old chicken-and-egg question. Where does DNA come from, if it can only be created by other DNA? Additionally, the DNA system is sometimes considered too complicated to have developed naturally via evolution, or as the aftermath of chance chemistry, which adds the possibility of outside intervention to the mix.

Regardless of how the first life on earth appeared, scientific evidence has deduced certain properties of the earliest living organisms. The composition of these primitive cells consisted primarily of water (H2O) and other earthly elements, such as carbon. Also, the free energy from the Sun assisted in the formation. Since no oxygen yet existed in earth's atmosphere, the first cells were anaerobic, meaning they functioned without metabolizing oxygen; likely they were also photosynthetic or some other form of autotrophic. What oxygen later existed in earth's atmosphere was the waste product of the early microbial creatures. Without the necessary means to convert the oxygen into usable substances, the oxygen would have been poisonous to the anaerobic cells, and so the massive quantity within the earth's atmosphere were pollutants that caused mass extinction among anaerobic surface dwellers. Cells eventually evolved to use oxygen in their metabolic processes, which allowed for further adaptations.

In addition to the technical questions, the philosophical inquiries of life's meaning and definition were explored. For example, the modern community has some difficulty quantifying the term “sentience.” This led to the question of the nature of consciousness. The class considered whether consciousness was an exclusively human construct, and if it served any adaptive properties. Also, the lecture considered where and when does consciousness begin. Although no specific queries were answered at the time, the class intended to revisit them at a different time. After examining the mysteries surrounding life, the class delved into other enigmatic questions with the intent of engaging them during a later session. Did any particular chemicals produce early life, or catalyze the first DNA? For a different take on the previous question, can it be assumed that DNA is irreducibly complex, meaning that it is too advanced to have evolved out of something else? Evolution only accounts for small advancements within a species, so at a cellular level, certain constructions could possibly be too complicated to stem from a combination of a few molecules. Furthermore, how did things like viruses come to be, since they do not fit within the typical prerequisites of life? How might life-forms function if they are composed of chemicals unlike the typical earthly variety?

An additional query delved into the prospect of artificial life. Creating living organisms out of raw matter is an exciting scientific prospect, made all the more intriguing in that it has not yet been done. Multiple efforts to spearhead the project have surfaced over the last two decades. American businessman and biologist Craig Venter has explored genomic research for years, and along with the aid of his eponymous facility (the J.Craig Venter Institute), plans to create a full-fledged synthetic life-form. The proposed organism is a bacteria that Venter terms Mycoplasma laboratorium, whose genome is based upon the known framework of the existing bacteria Mycoplasma genitalium. M. genitalium has the smallest known genome of any bacteria, and so it is comparatively easy to attempt to recreate than other single-celled organisms. Having mapped the genome of M. genitalium, Venter's team removed gene after gene until they discovered the bare minimum required to sustain life. The team then plans to synthesize this new genome from scratch, implant it in an M. genitalium nucleoid, and allow the new organism to replicate.

Although the seminar laid the groundwork for further examination of the mysteries of life, many questions will inevitably surface. The group agreed to discuss matters in greater depth throughout additional sessions that would each cover a more specific topic, thus providing for a greater focus on a single issue. Until then, the sessions plan to continue examining the questions at hand concerning life, its origins, and its future.