Lichen

"That slowly? Really?"
"Yes. Each of these large spots would have needed years or even centuries to grow this large."
"And all that structure! It seems so complex."
"It sure does. But it isn't. Those lines are just the most convenient way of transporting nutrients throughout the organism."
"Wow. Just wow!"
"Actually, it isn't even a single organism. It's more like symbiotic life. Do you see that green hairy patch? That's half the puzzle, we think. Produced oxygen. Still does, by the way."
"I see. But that couldn't have sustained itself, could it? Not like that. It would have had to rely on more mobile organisms for their food supply, maybe even something fungal."
"Exactly. But you know what's really strange?"
"No?"
"We couldn't find any of those fungi anywhere. Or residue of it, for that matter."
"Strange. And what are these pointy structures on the left?"
"We don't really know. Might be sediment left by those same missing symbionts."
"They look so beautiful and full of detail! But still, they are so flat! Why didn't they use the available height? That would have given them so much more efficiency."
"I agree. But apparently one doesn't become a dead end in evolution without some considerable blind spots."
"And how did they multiply? Did it have spores or something that could be spread through the atmosphere?"
"What I've discovered so far, indicates they never even left this single surface. The just spun those tiny lines and created more spots in empty spaces. Do you see them?"
"Barely. It's just so intriguing. I feel almost sorry that we have to clean it out. Even a boring life deserves a chance."
"Well, we need to get the silicon back. We don't want it contaminated with all kinds of sticky stuff."
"Just imagine they would have known."
"What?"
"That they lived on an old burnt out computer core."
"They couldn't. This is a very primitive life form."
"You really wouldn't have to be that smart. Everyone knows silicon is a very rare element. And the cooling water should have definitely given it away, even when there's almost nothing of it left."
"Okay, you win. Let's rub it off."