Factual evidence that the Earth have been visited by other civilizations

  Are we alone in the vast universe? This a very polemic question. Most of Scientist (Astronomers, Physicists, Biologists, etc.) state that no civilization has visited our planet. Nevertheless Prof. Abraham Loeb* has written a book describing the visit of an interstellar object called “Oumuamua” that passed 15,040,000 miles from Earth; it is opinion of Prof. Loeb that the object is a piece of advanced technology created by a distant alien civilization. Prof. Loeb based his hypothesis on the facts that Oumuamua was moving to fast along a strange orbit, it left no trail of gas, and the shape of the object was unusual. Long time before of the discover of Oumuamua, the astronomer Frank Drake** formulated an equation to estimate the number of civilizations in our galaxy that we might be able to communicate with. disc Drake's formula.png * Abraham Loeb is Israeli American theoretical physicist who works on astrophysics and cosmology. ** Frank Drake is an American astronomer and astrophysicist. Based on the ideas shared before: Is there any factual evidence that the Earth have been visited by other civilizations? Do you think is important to explore the Universe looking for signals from other civilizations? Make a quick research about SETI institute. Do you consider its mission is important nowadays?