Answer the following question given this paragraph: 

The generation of an isolated but open system, which we might call a protocell, was a critical step in the origin of life. Such an isolated system has important properties that are likely to have facilitated the further development of life. For example, because of the membrane boundary, changes that occur within one such structure will not be shared with neighboring systems. Rather, they accumulated in, and favor the survival of, one system over its neighbors. Such systems can also reproduce in a crude way by fragmentation. If changes within one such system improved its stability, its ability to accumulate resources, or its ability to survive and reproduce, that system, and its progeny, would be likely to become more common. As these changes accumulate and are passed from parent to offspring, the organisms will inevitably evolve, as we will see in detail in the next chapter. As in living systems today, the earliest steps in the formation of the first organisms required a source of energy to maintain the non-equilibrium living system. There are really two choices for the source of this energy, either light (electromagnetic radiation from the sun) or thermodynamically unstable chemicals present in the environment. There have been a number of plausible scenarios, based on various observations, for the steps leading to life. For example, a recent study based on the analysis of the genes (and the proteins that they encode) found in modern organisms, suggests that the last universal common ancestor (LUCA) arose in association with hydrothermal vents.60 But whether this reflects LUCA or an ancestor of LUCA that became adapted to living is association with hydrothermal vents is difficult (and perhaps impossible) to resolve unambiguously, particularly since LUCA lived ~3.4-3.8 billion years ago and cannot be studied directly. Mapping the history of life on earth Assuming, as seems likely, that life arose spontaneously, we can now look at what we know about the fossil record to better understand the diversification of...


Q: What is the theoretical event that began the universe often called?


A:
big bang