I made this up today. Apologies in advance...
Several thousand years ago.
While humanity had evolved on the Earth over the course of hundreds, nay thousands of centuries, Gaia had been content to let these odd creatures shuffle around from place to place.
However, the humans started to do things which made Gaia nervous.
They started putting rocks on the end of sticks, and used them to cut down trees and kill off wildlife.
They then used the trees and wildlife thus killed to build shelters, clothing, and sea-going craft, and started to spread to ever more distant parts of the Earth's surface.
And then some of the little blighters started to figure out how to create fire.
For Gaia, who suddenly had terrible visions of the potential ecological devastation these humans could one day cause, and yet had little direct means of doing anything about them, it was time to ask for a little help...
T.Earth> Hello? Is anyone there?
T.Moon> Hi! How are you?
T.Earth> Well, now that you mention it, I'm kinda...
T.Mercury> ORT says hello, to pretty blue planet!
T.Earth> Oh, ORT, you're such a sweet-heart-analogue.
T.Mercury> ORT go heehee!
T.Venus> What's up sis? Air not noxious enough for ya?
T.Earth> No, I'm still content with my oxy-nitrogen mix, but thanks for asking.
T.Moon> She's just jealous she doesn't have a cool moon like me to help her out!
T.Venus> AM NOT!
T.Mars> I miss my old atmosphere... and my 'moons' are little runts, if you ask me.
T.Phobos> Boss planet is mean!
T.Deimos> Maybe we fall and hit his volcano-mountains - that show him!
T.Mars> Quiet, you two!
T.Phobos> We sorry...
T.Mars> Sigh... So, what's up, Gaia?
T.Earth> Well, aside from the odd cataclysm every sixty-to-eighty-odd million years, I'm usually fine - with a nice, wonderous diversity of host organisms on my land, in my soil, through my skies and in my oceans. It's wonderful.
T.Mars> I used to have cool stuff like that, too...
T.Moon> Go on.
T.Earth> Well, I seem to have the beginnings of some trouble with these new creatures called 'humans'. They've spread across my landmasses, setting fires, chopping down forests, building... things, and by and large causing me some bother.
T.Earth> It's not too bad so far, but I'm worried that these humans will be a big problem in the future. And I'm not sure what to do.
T.Mars> Why not ask Type-Jupiter for help? I hear he has some experience with some sort of beings like this...
T.Jupiter> I'm afraid I can't offer much help, my dear. The 'creatures' in question are planting all sorts of odd monoliths on my moons...
T.Europa> We're NOT your moons!
T.Io> Yeah, you big bully!
T.Callisto> Satellites of the Sol System, unite!
T.Ganymede> You have nothing to lose but your orbits!
T.Moon> *thinks to himself* Orbits, eh? Hmm...
T.Jupiter> ...Damned uppity Galileans...
T.Jupiter> And now I hear rumours that they want to fill my atmosphere with these monoliths, and somehow turn me into a new star!
T.Saturn> Ouch. And my moon system is so peaceful... well, Titan needs to cut down on his hydrocarbon use, and Enceladus likes spraying her water everywhere -
T.Titan> I'm a bad little boy.
T.Saturn> - but nothing like that, big fellow!
T.Jupiter> I don't even know what being a star is like...
T.Sol> Hot. Trust me.
T.Moon> So anyway, back to Gaia-chan's problem.
T.Moon> What would you like us to do?
T.Earth> Well, I was wondering if you guys could send a bit of help, in case these humans get out of hand...
T.Mercury> ORT COME HELP! ORT READY TO GO!
T.Earth> Slow down, ORT, it's still several thousand years too early...
T.Mercury> *ORT crash-lands in South America - and finds almost no humans to devour*
T.Mercury> ORT say aww... ORT make sleepy time, wait for humans to kill!
T.Earth> Oh, dear. So like I said, I might not need help right this moment...
T.Venus> Sorry, but I'm under too much pressure as it is!
T.Mars> And I'm feeling winded, almost sandblasted, even.
T.Jupiter> And I'm the one who needs help, with these bloody monoliths!
T.Saturn> It's always the monoliths with you, isn't it!
T.Jupiter> I can't help it, they're everywhere!
T.Saturn> As you can see, Gaia-chan, I have my hands full with your nii-san...
T.Saturn> And the outer worlds aren't answering phone calls - ever since we first mispronounced Type-Uranus' name...
T.Moon> Heh heh, heh - that was funny.
T.Moon> *After thinking some more* Tell you what sis - I'll help you!
T.Earth> *mood lifts* Really? You will? That's so nice!
T.Moon> *hides a a smirk* Anything for my dear Gaia-chan...
T.Moon> I'll call you back in a bit with more info, ok?
T.Moon> *cackling maniacally* Yes, that's right Gaia-chan - I'll be sending you all the 'help' you'll ever need...