If we were to travel back in time approximately 4 billion years ago and observe the Moon from Earth, there would be some significant differences compared to its appearance today. Here's an approximation of what you might expect:
Proximity: The Moon was much closer to Earth in the past. The exact distance would depend on the specific time within that 4-billion-year range, but it is generally believed that the Moon was around three times closer to Earth during its formation. This means that the Moon would have appeared significantly larger in the sky compared to its current size.
Appearance: The Moon would have appeared quite different from what we see today. 4 billion years ago, the Moon was still undergoing intense volcanic activity, with volcanic eruptions occurring frequently. These volcanic events shaped the lunar surface, creating vast basins and maria (dark, flat areas on the Moon's surface) that are visible even today. So, the Moon would likely have had a more active and dynamic appearance, with a relatively smoother and darker surface.
Lunar Geology: The Moon's surface would have been in a more molten state during this time, and large impacts from asteroids and comets were relatively common. As a result, there would have been more widespread volcanic activity and a higher occurrence of impact craters on the Moon's surface. Over time, the surface would have cooled and solidified, leaving behind the distinct features we see today.
It's important to note that the specific details of the Moon's appearance 4 billion years ago may still be subject to scientific debate and ongoing research, as our understanding of early lunar history continues to evolve. The description provided here is based on current scientific knowledge and theories about the Moon's formation and evolution.