It might be useful to think of the phenomenon as some sort of "advanced non-human technology" and avoid the "ET" term altogether. Maybe it is possible that some intelligence found us before we found them; if it is more advanced and within range or was able to detect us somehow, we would be an attractive place to send devices to observe this oasis of life. We have a vast diversity of life that has evolved on this planet and has created so many different biomes and evolved in so many different ways in the midst of large parts of the galaxy that are vacant of life or don't seem to have highly complex life. Perhaps this is the only place within the range of the intelligence, that has life. I think curiosity might be a universal fundament of life, regardless of how or where it develops, and the need to explore and expand might be somewhat universal.
For me, there seems to be certain patterns of behavior that the phenomenon has exhibited over time, and I think that whatever it is, it has been here for a very long time. The "flash and dash" tactics, isolating people or small groups of people in "road encounters", the mass sightings where many are exposed to their displays before they shoot off and leave... Showy maneuvers around weapons testing and nuclear sites... Once you can establish the same type of phenomenon behaving in a controlled manner before we were flying around in the atmosphere --then I think there is no way to put a limit on how far back the phenomenon has been with us. At this point the objects may not be coming in from space on a regular basis, having had ample time to infiltrate the oceans, and other places on the planet, but if I may be allowed to brandish Occam's Razor momentarily, I think it is likely that wherever / whenever they originally came from, it is likely to be physically removed from this planet --even if they are coming from some sort of spacetime portal or something we can't even understand yet. I think the reason the Air Force has been so silent and others whine about sensors being compromised, is because UFOs are seen to be coming in from space periodically, and they seem to be coming in from space in many of the old accounts too; dropping in like shooting stars and then stopping dead in the air and moving off to do their thing. I am further inclined towards this explanation, as with my second sighting the capsule-shaped object / Tic Tac did fly off into space..
Many of these questions can be answered scientifically.
1.) Did they find us before we found them?
Yes. There are galactic green zones. Galactic green zone is place, or actually a ring, of width of about 1/3 of galactic radius where conditions are most favourable for creation of life. Planet Earth is place on the inner edge of this ring, on the side closer to the deadly galactic centre. There are many astronomical studies that addressed this issue and when its all said, done and all statistics is calculated, it comes out that an average Milky Way green zone civilisation is 2.0 Billion years older then ours. So,
aliens have, on average, 2.0 billion years civilisational and technological advantage over us, just by being born in the right place at a right time. Don't let anybody sway you on this one, this is rock solid.
2.) What are aliens doing on Earth?
Simply doing science. Watching and collecting samples. There are millions of uninhabited planets in Milky Way and hundreds of thousands of planets with life. Everything that we have here, is available on any of these millions of planets. You want tons of iron ore? Go to Mars or asteroid belt and dig up as much as you like. In other words, aliens need none of our resources, because they are available everywhere.
From a point of view of a civilisation that is 2.0 billion years ahead of us,
Earth is in no way special. Only we think we are special. All the upstarts think they are special.
What are our scientists who are studying animals in Africa doing? They are watching them, tagging them, inserting chips into them and occasionally hunting animals down and cutting them up to study anatomy and biochemistry of these animals. And these is major theme in UFO encounter. I don't know how many times I've read an UFO story were witness caught aliens while they were in a middle of wood or a farmer's field collecting plants.
This is precisely what explains the frequency of alien visitations. Its hard to say, but by broadly estimating from number of MUFON cases I would personally have impression that there are around 1,000 serious contact cases per year in the whole world. That's not enough to mount an invasion or mount a threat. Its just for keeping an eye on things.
3.) Are aliens threat to us?
Stupidity of this question really makes me sick. If aliens are 2.0 billion years older then us, they had been visiting Earth for at least few million or few thousand years.
Did aliens ever attack us on mass during all this time? Well, answer is NO! They have no reason. They've got everything we want, so they don't need to.
Some people keep talking about security and there is a danger that by repeating this idiocy a culture of hate towards aliens will be created. As I explained above, apart from a negligible number of abductions and carving ups for science, aliens can't care less about attacking us. Numbers of harmed humans is so small that we simply have to put up with it, at least until we catch up technologically.
Presence of aliens actually makes for a huge economic, technological and cultural opportunity for all of mankind and
we should be making active efforts to develop proactive and mutually beneficial relationships with alien civilisations.
.