New research has pinpointed a "sweet spot" in Earth's ancient history—around 4.33 billion years ago—when conditions were most favorable for the RNA World, a hypothetical phase in the early evolution of life. During this time, RNA, a molecule similar to DNA, may have been the primary replicating substance, forming the foundation for more complex life. This period likely began as early as 4.4 billion years ago, according to a study published in Nature Communications. This timeframe follows the end of a heavy period of asteroid, comet, and other space rock impacts that bombarded the early Earth. The study, led by Oleg Abramov of the Planetary Science Institute, offers a more precise estimate for the onset of the RNA World than previous research, which had suggested broader time ranges. Earlier studies placed the RNA World between 4.46 and 4.26 billion years ago, and even as early as 4.45 to 3.9 billion years ago. Abramov’s work narrows this range significantly, aligning with earlier estimates but reducing the uncertainty to just a few million years. The RNA World is thought to have existed before the Last Universal Common Ancestor (LUCA), the single-celled organism from which all modern life descended. RNA is a single-stranded molecule that plays key roles in cellular processes and is structurally similar to DNA. Scientists believe that RNA was the first molecule capable of self-replication, allowing genetic information to be passed from one generation to the next. Over time, RNA evolved into the more stable DNA, and life transitioned into a world where proteins and DNA coexisted. To determine when the RNA World might have existed, researchers built a computer model of Earth's interior to simulate the effects of massive impacts between 4.5 and 3.5 billion years ago. These impacts, which included space rocks hundreds of miles in diameter—far larger than the asteroid that caused the dinosaur extinction—were so intense that they likely sterilized Earth’s surface. The bombardment may have caused widespread melting of the crust, vaporization of oceans, and extreme temperature fluctuations. However, by 4.4 billion years ago, the frequency of such impacts declined, allowing conditions to stabilize. As the bombardment subsided, hydrothermal vents formed in the crust, creating environments rich in the building blocks of RNA, such as nucleotides, peptides, and lipids. These vents may have provided the necessary conditions for the RNA World to flourish. The study suggests that the RNA World may have lasted up to 130 million years before giving way to LUCA, which is thought to have appeared around 4.2 billion years ago. However, the exact duration of the RNA World remains uncertain, and further research is needed to refine these estimates.