There are billions of galaxies and each galaxies has billions of stars. According to Drake Equation there at least 10,000 advance civilization in our Milkyway galaxy. They are not going to visit earth and do an airshow over Phoenix nor abduct people and do medical experiments. This airshow has logical explanation and no aliens are involved.
When humans want to learn about animals in oceans or animal in wild what do we do ?
a) We observe their habitat
b) We analyse their behavior
c) We ride in safari cars but we don't make physical contact we stay
hiden
d) We also sometime cut them open to learn about their operation
mechanism and mode of life
The Aliens who are visiting are likely on observation mission to understand how we function , and why are we destroying the vary earth that gave us birth , from above in sky our cities might look a unusual growth on the surface of land, so they might be curious why do we insist on building these lit up roads that shine in night. And why do the roads have these flashing items with lights luminating from em (cars). From view point of an alien , when they might look at our streets and highways it might appear like how we view blood cells moving thru veins when we view thru microsope. We know these cells are living and alive but we can't communicate with them , similarly the aliens may not know how to communicate with our primitive forms.
They might visit our planet , to examine it from far, and enjoy its animal life just like how we examine animals in African sufari and noting more, we have tanks , and fighters to eliminate all animals in Africa but we don't do that , obviously - the aliens also have no need for our destruction.
Of course if they do have taste for animal meat we might have some problems.
As far as for the technilogical aspect , their race may have formed 1-2billion years ahead of life's evolution on earth , so they might posses technology that is more advance then ours.
The only chance we have to make contact is a craft malfuntions and falls into a city
Yesterday I was seeing a show on marine biology
It stated, that if our water currents stop , if all ice on earth melts then our oceans will start emiting sulphuric gases , as the microbes that thrive in stale water will take over 100% of oceans , and they will not only kill all life but will also change oxygen in atmospher into something poisonous.
Furthermore, they also stated that in earth there are places underwater
0% light , and temperetures boiling hot levels, minerals emiting from ground vents
and total darkness!!! Photosentesis does not exists !!! and even in that harsh environment LIFE EXISTS!!!
a) No oxygen , only sulphar and mineral rich environment
b) No sunlight no photosynthesis and still life exists
We assume that life needs oxygen ...but not always ...