Given the number of galaxies and planets, it is unlikely that Earth is the only planet where (intelligent) life exists. However, it seems unlikely to me that they would visit us.
I base this on my own experience. I personally don't feel like visiting Australia or New Zealand because I don't like the 22 hours of flying to do so.
I cannot imagine that there is intelligent extra-terrestrial life that would want to travel millions of years to poke around here (but then again, who am I?).
The series Ancient Aliens, on the History Channel, shows remarkable phenomena: Buildings that are 10,000 years old, constructed with technologies that could not have existed at the time. The conclusion is always: ‘Those people back then could never have done that independently. This is proof that Aliens must have been at work here.’ My idea is that people were simply much more developed then than we now assume.
Everything has a beginning and an end. We assume that Homo Sapiens originated in Africa a hundred thousand years ago, then wandered to all corners of the earth and continued to develop from there. That development is less linear than assumed: Cultures (and technologies) developed and disappeared again.
A characteristic of Homo Sapiens is the large brain size. This is useful if you want to understand string theory, but according to biologists, the evolutionary advantage of the large head during the hunter-gatherer era is not obvious. At that time, most people died from lack of food. An energy-consuming brain is not really an advantage.
The intellect, in my opinion, generates a certain unrest. As a result, people started walking and always tried to push their boundaries.
More than 10,000 years ago, this meant that impossible construction projects were realized at that time.
We assume that ten to fifteen thousand years ago humans switched to agriculture.
There are no traces to be found from before that time. Actually, we have no idea what exactly people did before that time and why it took so long for them to start farming.
That civilizations existed much longer than ten thousand years ago seems more likely than that they were helped by aliens. It is just very difficult to find objects from that time.
Ceramic artefacts are buried too deep and metal objects are completely dissolved over time.
It was also long believed that Columbus was the first European in America. Now there is evidence that Scandinavians settled in North America more than four hundred years earlier and that Knights Templar visited Nova Scotia as early as the 12th century. History changes from time to time.
We often see large gaps in the historiography. When we look at Central America, the first thing we see is a large jungle.
The Olmec lived there about 6,000 years ago. A civilization that existed for perhaps 1000 years, but then disappeared again. When the Spanish came (around 1500), the Mayans lived there.
Between the Olmec and the Mayans, one or two more cultures emerged and disappeared again in a time gap of 3,000 years.
The Bronze Age started about 5,000 years ago in the Middle East. This is actually another assumption. It is difficult to date a bronze object exactly, especially if it is very old.
Metal anchors were used in a 10,000 year old structure. However, nothing of the metal can be found. If humans have existed for about 100,000 years, why was the metal only discovered after 95,000 years?
JMM, 2023
More information on this subject: Youval Noah Harari - Sapiens