Have extraterrestrials visited Earth in the past?

Answer 1

I think they have because Earth is billions of years old and there has been enough time for them to do so, but if so, they must have been incredibly careful or have visited very seldom, because there is no sign of them in the fossil record, no sign of any alien artifacts and no life-forms with clearly foreign genetic material.

Answer 2

I am no expert, but I shall try to break some stuff down. Big Bang Estimates put the universe to be abour 14 billion years old, with our planet being around 4.5, Billion years. Lets assume that it took 4 Billion years for the universe to reach a supportable life state.

Between the formation of the Earth and Liveable period we have a gap of 5.5 Billion Years. Now, assuming that Mr Alien and Co's planet formed in this time, and so have had an extra 3 Billion years of evolution and technological development, it is possible that they have been able to reach us.

The big questions, How, and why?

Why is the first question to answer. Assuming Mr Alien measures and looks the same as us. I.e. looks for radio waves and light, unless he was within a few million of light years, he would not see a planet that was habitable until we had evolved. Now, assuming that Planet Alien wants to make a visit to the Little Chef for some 5 star food, he would need to build space ship. Lets say that our current laws of physics hold and so nothing can travel faster than light, it would take a further few million years to get here, equally when they got here and found nothing but us lot, it would take a further few million years to send any data back.

In which case all his friends are dead. So why bother?

Answer 3

Although it's conceivable that there's life elsewhere in the Galaxy, the likelihood of a visit from extra-terrestrials is infinitesimal.

It's logically possible, but look at some elementary calculations by way of a sanity check.

There are about 10^11 stars in the Galaxy. Suppose one in ten have planetary systems. That's 10^10 stars. Suppose one in 100 of these could support life; that's 10^8 stars. Most are considerably smaller than our Sun, so around one in ten of those can be considered reasonable candidates for supporting life. That's still ten million stars in our galaxy alone capable of supporting life, of which say one in ten have developed living systems, so a million stars with life.

The volume of the Galaxy is around 10^14 cubic light years. This give around 10^8 cubic light years volume on average for each star which supports life. Thus the average distance between life-supporting solar systems is about 500 light years.

However, this calculation assumes that life-supporting systems come into existence simultaneously, whereas they will come into existence (and fade from it) at different times. The duration for which a star has a 'life-friendly' zone is only a small fraction of its lifetime on the Main Sequence. Even if the lifetime of any civilisation is as long as 100 million years, when spread over the 10-15 billion year history of the Galaxy this would result in fewer than 10,000 stars supporting life at any one time. This means that the average distance between neighboring civilisations jumps from 500 light years to 2,000 light years.

Not only would the energy cost of doing this be (quite literally) astronomical, you'd have to work out why one star should be 'targetted' for a visit over another. So enormous would the putative cost be that you'd further have to 'discount' the proportion of solar systems being advanced enough to even think about it, which in turn increases the average distance still further.

Sadly (or happily), the probability that Earth has been visited by extra-terrestrials cannot be differentiated from zero by the width of a photon.

Answer 4

There were some UFO pictures that were taken in the past years but none have shown official extraterrestrial pictures.

Answer 5

I do not belive that extraerrestrial ""Aliens""" have visited us..
maybe, it had happened. but not in the presence of man since.

Maybe, some microscopic life from comets, asteroids, meteorites may have accidently came to earth from them..
and maybe, the life have started from it.....


But i do not belive that extraterrestrials LANDED on earth.

Answer 6

I have always thought that we are not alone and read lots of books, visited lots of web pages about extraterrestrials.
Here are links to an author that I really reading back in the 70s and still look back at his books every now and then.
This is the kind of stuff that keeps my brain busy for hours at a time

http://www.daniken.com/e/
http://en.wikipedia.org/wiki/Erich_von_D%C3%A4niken
http://www.evdaniken.com/ :)

Answer 7

No, they did not. Distances between any planets that might have intelligent life are too vast to travel between them. No material object can travel at the speed of light, since it has inertia that increases exponentially if one comes near light speed. One could burn the universe to power a spaceship, and it still would not achieve light velocity. The nearest star to our Sun or Sol is Proxima Centauri that is about 25,000,000,000,000 miles away. At our escape velocity, it would take 106,448 years for a ship to travel from it to visit us. That stuff about "warp drive', etc. is fantasy. Scientists have refuted such men as Eric von Daniken who invented a wild tale about ET's guiding us in the past to make money from his books about such nonsense. He had been convicted for theft before.

Answer 8

It's very unlikely and there is no evidence that any have (though a lot of kooks have claimed to have such evidence).

Answer 9

people are saying its unlikey if they have and are firgetting about roswell new mexico. the alien craft fell there and when it was reported it had moved andit moved to a secret location well it aint that secret anymore it was an submarine acrrier and it was moved to there and then moved to a top secret location so yes we have been visited by aliens in the past

Answer 10

Of course they have--Do you think a bunch of Egyptians could have built all those pyramids and kept them in line to within one degree of the ones in Mexico?