The Spark of Life
The source of life on Earth is possibly one of the greatest mysteries in science. There have been several explanations, but none can be verified. In order to discover this information we must gain an understanding of the geochemical environments where initial life forms flourished. Water, subjected to certain temperatures and rotations, set forth chemical processes that led to the creation of life in our world. Because life arose in the largely unknown surface conditions of Earth’s early history, answering these remains a challenge.
Many essential things matter to life. We have carbon, hydrogen, oxygen, nitrogen and phosphorus. However, several scientific puzzles concern how these elements ended together on Earth. For example, it is not expected that a planet so close to the sun would naturally incorporate carbon and nitrogen. These elements take only solid form under extremely cold temperatures found in far areas of the solar system, while Earth is much closer to the sun where such temperatures do not exist.
Additionally, carbon is rare at the earth’s surface. This is because they stay chemically bonded to iron more frequently than rocks. So how were they found on the surface of the Earth? Could a similar process also occur on other planets in the universe?
The final component is water (H2O). Presently on this planet, approximately seventy per cent (70%) of its surface is occupied by water, but what was there on the outermost layer some 4 billion years back? Like carbon and nitrogen, water is much more likely to form at a greater distance from the sun than the Earth.
Prebiotic Chemistry: The Base of Life
Prebiotic chemistry is a field that deals with the study of how organic compounds were made and self-organized before the dawn of life on Earth. This process describes the chemical mechanisms that could have been responsible for the emergence of life, mainly focusing on the constitution of some simple types of organic molecules and the formation of more complicated ones. Early conditions of Earth around 4.5 billion years ago were very different. Earth was volcanically active and its atmosphere consisted of only very simple molecules. There was no oxygen, but the presence of other gases like methane, ammonia, and hydrogen was observed. These conditions promoted the chemical reactions that would finally evolve into life. The first step in prebiotic chemistry is the formation of simple organic molecules from inorganic substances. This process was mainly put forward by various energy sources such as lightning, ultraviolet radiation, and volcanic activity.
Once simple organic molecules like amino acids and nucleotides were formed, they could be linked together to form polymers such as proteins and nucleic acids. This process is known as polymerization. This could have occurred on mineral surfaces or in small pools of water where concentrations of these molecules were high. Simple cell-like structures that could have formed from the spontaneous assembly of lipids and other organic molecules are called Protocells. These structures would have provided a compartmentalized environment, allowing for more complex chemical reactions to occur. This is considered a crucial step towards the development of true living cells.
Miller-Urey Experiment
Back in the 1950s, two American chemists, namely, Stanley Miller and Harold Urey, designed a now famously known experiment to create these amino acids from what they believed was the composition of the early Earth’s atmosphere. It is one of the first successful experiments demonstrating the synthesis of organic compounds from inorganic constituents in an origin-of-life scenario. The experiment used methane (CH4), ammonia (NH3), hydrogen (H2), in a ratio of 2:2:1, and water (H2O). Applying an electric spark to simulate lightning resulted in the production of amino acids. It is regarded as a groundbreaking experiment. Later scientists examining the original experiments were able to show that more amino acids were produced in the original experiment than Miller was able to report. While evidence suggests that Earth’s atmosphere might have had a different composition from the gas used in the Miller experiment, prebiotic experiments continue to produce mixtures of simple-to-complex organic compounds. Moreover, scientists believe that more suitable factors would have occurred after the impact of large asteroids on early Earth.
RNA: A Self-Replicating Molecule
RNA (Ribonucleic acid), a molecule similar to DNA (Deoxyribonucleic acid), is capable of both storing genetic information and catalyzing chemical reactions. The RNA world hypothesis states that RNA is the first self-replicating molecule, which serves as the base for the development of DNA and proteins. It also suggests that life on Earth began with a simple RNA molecule that could copy itself without any help from other molecules. DNA stores the information for building living things from bacteria to animals. And proteins which lead to the chemical reactions needed to keep cells alive and healthy. RNA was thought of as little more than a messenger between DNA and proteins, carrying instructions as messenger RNA to build proteins. However, RNA can do far more. It can drive chemical reactions like proteins and carries genetic information like DNA. Since RNA can do both of these jobs, most scientists think life began in an RNA.
The Role of Asteroids
The Panspermia hypothesis suggests that life must have originated somewhere else in the universe. This also states that life could have travelled on comets or asteroids, seeding life on our planet. Two recent space missions that aimed to collect samples from asteroids are NASA’s OSIRIS-REx and JAXA’s Hayabusa2.
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) was launched by NASA on September 8, 2016. The mission’s primary goal was to collect samples from 101955 Bennu, a carbonaceous near-Earth asteroid, and return it to Earth. The spacecraft successfully collected a sample in October 2020 and returned it to Earth on September 24, 2023. Initial analysis of the sample revealed the presence of carbon and water.
Hayabusa2 is a successor to the Hayabusa mission which returned asteroid samples in June 2010. This mission by the Japan Aerospace Exploration Agency (JAXA) was launched on December 3, 2014. The spacecraft travelled to the asteroid Ryugu, a C-type (carbonaceous) asteroid, where it collected samples from the surface and subsurface. It returned the samples to Earth on 5 December 2020. The mission provided valuable insights into the composition of asteroids and the early solar system. These missions were significant milestones in space exploration, providing critical data that helps us understand the origins of our solar system and the source of life on and beyond Earth.
Conclusion
The conditions under which life initiated on Earth are one of the most fascinating and intricate questions in science. From hostile early-Earth environments and different hypotheses like abiogenesis and panspermia, each theory puts forward its own interesting and viable explanation of how life might have started. Experiments such as the Miller-Urey trial and the catalytic roles of RNA have seen significant advances. However, a myriad of other questions are still in the world of science. These questions have motivated scientists to propose compressive strategies with laboratory simulation, computer modelling, and the analysis of life in hostile environments. Indeed, there is a great potential likely to be realized through the detailed examination of other planets and moons for revealing new information on the conditions that might support life. Although we have taken huge steps, it is an ever-continuing journey into the understanding of the origin of life, and with each discovery, we just get a few steps nearer to answering the ultimate question.
