Final answer:
On the cosmic calendar, which scales the universe's history to a single year, the Big Bang occurred at the beginning of January 1. Human history is depicted as starting in the evening of December 31, showcasing our recent emergence relative to the universe's lifespan.
Step-by-step explanation:
According to the approximation used in the cosmic calendar concept, the Big Bang occurred at the first moment of January 1. This calendar compresses the entire 13.8 billion year history of the universe into a single year for visualization purposes. Significant milestones in the cosmic calendar include the formation of our solar system on about September 10, and the appearance of the oldest rocks we can date on Earth around the third week of September. This interpretation of time illustrates the evolution of the universe in a more comprehensible scale, where humanity's appearance is rendered in the final moments of December 31st.
Such a calendar helps us to realize the vastness of the cosmic timescale and our place within it. The development of humans did not happen until the evening of December 31 on this scale, highlighting how recent human history is compared to the age of the universe. Another milestone, the time when the universe became transparent to light, happened about 380,000 years after the Big Bang, which would be represented as a date in this cosmic year as well.