Hint: The modern theory is also known as a chemical theory or naturalistic theory or primary abiogenesis or Oparin Haldane theory. The idea of abiogenesis is life always comes from preexisting life.
Oparin and Haldane held that spontaneous generation of life under the environmental conditions is not possible. Earth’s surface and atmosphere during the first billion years of its existence were radically different from today’s condition.
Earth’s initial atmosphere was a reducing one. The first life arose from a collection of chemicals through a progressive series of chemical reactions in which atoms combine into inorganic molecules, inorganic molecules into simple organic compounds, simple organic compounds into complex organic compounds, polymers into aggregates, which finally got organized into living matter.
Several organic molecules like polypeptides, polysaccharides, polynucleotides, and fats gathered to form a coacervate. These coacervates were capable of dividing by budding. A layer of water and fats surrounded them. They were present in hot seawater, which provided conditions for their metabolism. This led to the appearance of the first cell. This abiogenesis occurred about 4 billion years ago. Solar radiation, heat radiated by earth, and lightning provided energy for the evolution of molecules.
Since a lot is known about the metabolic processes today, life can be created in the lab. Urey and Miller successfully demonstrated the precipitation of a coacervate-like structure in their famous lightning experiment. Hence, life can be created in the lab today.
Note: The Oparin-Haldane theory was not immediately accepted as it lacked supporting evidence, However, it was experimentally supported by Stanley L. Miller in 1953.