By the time they left, we couldn’t look at ourselves the same way again. They’d come looking for a marvellous treasure, following the clues across the galaxy, searching through the DNA reservoirs of a thousand species to find the signposts and clues left by a long vanished race. Then they found us, when they came to Earth, Terra, Gaia or whatever you want to call our world.
They kept themselves a secret at first, sampling animals in discreetly at night. They were, after all, one ship of adventurers and we, although relatively primitive, were a planet of billions. When they moved on to sentient samples, first they abducted a few locals in a remote region for testing, then a few more in another region. Not liking the answers they’d gotten so far, they sampled more and more populations. Eventually, of course, they got caught on video on someone’s phone. [The manufacturer of the device was thrilled with the publicity for their brand.] Their secret was out, aliens were here.
It took us a surprisingly short time to track them down. Apparently that matched with the answers they didn’t like. By the time they realised we’d found them, we’d blocked their lift path out and they had to talk to us. It took a week to develop meaningful communication and a month more before they could persuade us to let them leave.
We didn’t kill them. We didn’t fly them into Jupiter but our telescopes and other instruments saw them smash into the massive planet. We didn’t understand why.
Then we found they’d left a beacon. A beacon with a message. They’d already told us what the message in the DNA, all our DNA, said. It took a while to decode the beacon message but we managed it. Then we pondered the motives of this long vanished race and planned to recover the beacon so we could take it apart to see how it worked. It would go with the pictures we’d taken of the adventurer’s ship to help us build our own ships.
“This is our booby trap planet, you probably won’t make it off alive. Whatever intelligent live has evolved here will follow you to the stars, now they know it can be done.”
“Plague world, stand clear. Plague world, stand clear.”
Two messages from the dead.
One dead race used us, and all our potential alternate possibilities, as a threat to whoever followed their trail.
The adventurers were dying when they took that plunge. The galaxy is out there, we just have to be careful not to get our germs on it.