The age-old question, “how did life begin?” has baffled humans for centuries. Many scholars have theorized about how life began, but in almost every case, they have agreed on one thing: in some way, the creation of life involved water.
Some of the earliest recorded scientific theories about life’s beginning date back to ancient Greece. Due to its abundance, scholars such as Thales the Milesian believed that water not only sustained life, but created it as well. Thale’s student, Anaximander, did not believe that water was responsible for creating life directly, but rather played an important role in developing life after creation. More specifically, he developed the idea of that life was ‘spontaneously generated’ from a form of inexhaustible matter called Apeiron.
Fast forward a few centuries to 1871, and we find another scholar who believed that water was central to life’s creation: Charles Darwin, who developed the warm pond model. In a letter to botanist Joseph Hooker, Darwin poetically stated that the first creatures on Earth may have originated in a small, warm pond containing a primordial soup of elements that set forth the creation of proteins, and later, complex life.
It wasn’t until 1953 that the infamous Miller-Urey experiment aimed to tackle this complex issue with conviction. Stanley Miller and Harold Urey, both biochemists, conducted an experiment that demonstrated that if they could create the conditions thought to be present in the Earth’s early atmosphere, amino acids (the building blocks of proteins) would form spontaneously.
Influenced by Darwin’s ‘primordial soup’ idea, the scientists pumped methane, hydrogen, and ammonia, what they believed to be the primary components of the early atmosphere, into a closed apparatus containing boiling water (Figure 1).
As the gases circulated and mixed, Miller and Urey subjected the mixture to a high voltage electrical discharge that resembled a bolt of lightning. The mixture then passed through a condenser to cool down before it reached a trap that collected the products of the reaction. After a week, they saw that the liquid turned into a dark brown color. Upon analysis, Miller and Urey found organic amino acids! These findings were so profound that even Time magazine wrote a piece on it entitled, ”Semi-Creation.”
Despite these ground-breaking results, other scientists have since picked apart the Miller-Urey experiment for its many flaws. For example, most scientists believe that the gasses used in the experiment did not actually resemble the atmosphere in the earlier days of Earth’s development. Instead, geological data strongly suggests that the early atmosphere was much more likely dominated by carbon dioxide, water vapor, and nitrogen. Also, the amino acids Miller and Urey found in the brown liquid included some that, in some circumstances, can disrupt our protein function and kill us.
The experiment also assumed that a single spark of lightning may have been all that was needed for life to start and continue to evolve to where we are today. But this assumption emphasizes one of the experiment’s biggest limitations: Life has become significantly more complex than a random collection of amino acids, and these biochemists did not answer the question of how the Earth created complex proteins, cells, and ultimately, plants, animals, and other organisms.
So, what happened next? Well, like Thales the Milesian and Anaximander centuries before, scientists began to look to the oceans for answers. And not just any part of the ocean, but the deepest, darkest areas of the ocean where most people would assume life doesn’t even exist. But it does.
In 1979, a team at the Scripps Institution of Oceanography discovered volcanic fissures in the ocean floor that became known as hydrothermal vents or ‘black smokers.’ Despite the crushing pressure of the ocean above, the lack of sunlight, and the presence of 750°F, superheated water released by the vents below, scientists found a thriving biological community near the ocean floor that included shrimps, tube worms, and fish. This amazing discovery began to beg the question, if life can evolve with great success in such a harsh environment, did it also start here?
This is where some of the most recent research on the origins of life begins. Dr. Nick Lane of University College London, one of the prominent scientists in the field, believes that the first single-celled organisms may have developed 3.7 billion years ago in alkaline-rich vents on the sea floor. These vents are characteristically different to the ‘black smoker’ vents oceanographers study today, mainly in that they are more warm than superheated (Figure 2).
Lane’s theory of the origin of life suggests that the interaction between the warm alkaline (or basic) vent fluid and the early acidic ocean water may have had a large role to play in the development of the earliest organisms. But how exactly does this work?
If the ocean were highly acidic, this means the water would have been full of positively charged protons, like hydrogen (H+). At the same time, deep-sea alkaline vents would be releasing negatively charged ions like chlorine (Cl–) into the surrounding water. The positive and negative ions would be separated like in a battery by tiny pores found within the vent, creating voltage. It is thought that the electrical charge created by this voltage powered the creation of simple carbon-based molecules such as amino acids and proteins from carbon dioxide and hydrogen. As time progressed, the gradient began to shape cell membranes and power the creation of self-replicating molecules such as DNA.
At this time, however, these primitive cells had nowhere they could travel to get food, which means they had to depend on the pores within the vents to supply them with their energy. Just like the Duracell bunny, the only way the cells could move out of the vents into the surrounding ocean would be to carry an energy pack with them. This theory led scientists to start studying archea, a domain of single-celled organisms (which happened to be discovered by University of Illinois professor Carle Woese). These scientists found that the archaea living near the vents operate simple pumps that act a little bit like wires attached to a battery: they push positive ions across their cell membranes, which helps power their cellular processes. Many scientists believe that an earlier form of this pump developed in the earliest cells and allowed them to utilize ions in the open ocean to provide them with energy so they did not have to depend on the vents themselves. The ability for cells to power themselves independently presumably set the ball rolling for more complex life to evolve.
Is that the end of the story? Not quite. Even though studying these ideas in the laboratory has proven to be tricky , Lane has been able replicate the chemical reactions that occur in the vents, and has created small quantities of proteins. Lane has said his work shows that his theories about the deep ocean are plausible.
Although there is still a lot more work to do, this area of research is by far one of the most exciting in our times. For more information on the topic, I highly suggest watching a 30-minute lecture by Dr. Lane by clicking here.
Ellis Moloney is a master’s student in applied aquatic biology at the University of Portsmouth in the United Kingdom. Ellis writes his own blog, The Science Rationale, and you can find him on Twitter @Ellis_Moloney.