The best evidence we have is the Stanley-Miller experiment carried out in 1953, which is as follows:
In 1953, Stanley L. Miller and Harold C. Urey, working at the University of Chicago, conducted an experiment to understand the origin of life. Miller took molecules which were believed to represent the major components of the early Earth's atmosphere and put them into a closed system. The gases used were methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). Next, a continuous electric current was passes through the system, to simulate lightning storms believed to be common on the early earth. Analysis of the experiment was done by chromotography.
At the end of one week, they observed that as much as 10-15% of the carbon was now in the form of organic compounds. Two percent of the carbon had formed some of the amino acids which are used to make proteins. Thus this experiment showed that organic compounds such as amino acids, which are essential to cellular life, could be made easily under the conditions believed to be present on the early earth.