1. In 1775, the first meeting of the Pennsylvania Committee of Safety occurred in Philadelphia. The committee was formed to oversee military preparedness in the colony and played a critical role in the American Revolution.

2. On March 23, 1832, the Pennsylvania Legislature passed the Act for the Gradual Abolition of Slavery, which prohibited the further importation of enslaved people into the state and set a timetable for emancipation of those who were already enslaved. Although the act did not free all slaves immediately, it was a significant step toward abolition.

3. In 1842, Pennsylvania Railroad opened its first track, running from Philadelphia to Columbia. The railroad was a major transportation hub in the state, connecting Philadelphia to Pittsburgh and beyond.

4. On this date in 1978, the Three Mile Island nuclear power plant near Harrisburg experienced a partial meltdown, resulting in the release of radioactive material into the air. Although no fatalities or immediate injuries occurred, the incident was a significant environmental disaster and led to increased scrutiny of the nuclear power industry.

5. In 2017, Pennsylvania became the 24th state to legalize medical marijuana. The law allows for the use of medical cannabis to treat a variety of conditions, including chronic pain, cancer, and epilepsy. The move was seen as a significant step forward in the state's efforts to provide patients with alternative treatment options.