They are green, mostly.
They don’t eat, pee, or defecate.
Some may be smaller than your little fingernail, but others may be hundreds of feet tall and weigh thousands of tons. (Indeed, they may be the largest life-forms on Earth.)
They may also be the oldest. Some of them can live to be thousands of years old.
Even though some of them may live for centuries, they all spend their entire lives, and die, in exactly the same spot at which they were “born”. (Unless something or someone physically moves them.)
They live outdoors, mostly, but sometimes they live inside our houses and apartments, even our bedrooms and bathrooms.
They’re everywhere. They’re all around us. But we don’t “see” them.
That is, we can see them, but most of the time we simply don’t notice them.
We don’t pay much attention to them mainly because they don’t move. (Actually, they do move, but usually they move so slowly that unless we are very attentive, or use time-lapse photography, we don’t observe it happening.)
Although we ignore these aliens most of the time, we are totally dependent upon them for our very existence.
We’re dependent on them because they provide us the food we eat and the oxygen we breathe.
These “alien” life forms, of course, are plants.
Plants are “alien” because, at least superficially, they couldn’t be more different from us (even though we share common cellular ancestors).
They’re “alien” also because they are directly connected to the physical world in ways that we are not.
That is, green plants are able to survive and grow by directly using sunlight, air, water, and a few minerals from the soil, and we certainly can’t.
Because we can’t, we are absolutely dependent on plants’ ability to use energy from the sun to convert air, water and minerals into biomass (with a nice byproduct called oxygen).
And, of course, we depend on plants not only for the food we eat and oxygen we breathe, but also for materials we use to shelter and clothe ourselves and for fuels to power most of our machines.
Despite the fact that we are so absolutely dependent upon them, that they’re all around us, and that they’ve been on Earth hundreds of millions of years longer than we have, most of us know very little about them.
So, this is another way in which they are “alien”.
That is, to most of us, they are unfamiliar, strange, and unknown.
Maybe people should try to get to know them better.
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