That's when they constructed some clever traps and caught several of us. In fact, three of us that I know of were killed by your race. The boss responded in a fit of livid rage. From there on out things got very hectic. He ordered us to find a way to wipe all humans off the face of the planet. We got to work on it right away, even while reminding the boss that the master would never let him get away with it. (How did we know? That, again, is related to the boss's first plan -- the one that failed. It's far too complicated for me to explain here.) The boss said to do it anyway.
He and the leaders of all the squads met and took over a year developing a plan. It was both simple to execute and extremely complex in all the benefits that would accrue to us. You see, even before the boss got done planning what to do our intelligence operations discovered that the master planned to let us get away with it. It was a good news, bad news type of announcement. The bad part was that the master had a plan to allow a small, select group of humans to survive the operation.
When the boss and our leaders announced the final plan, it included a brilliant strategy for hiding both the work we had already done and any work we might undertake in the future. The most astounding feature of the plan is that all we had to do was convince a few of you to undertake an unusual but feasible plan. For the sake of brevity I will cover only the major portions of the plan.
Your planet originally had two moons. These were equal in size and 90 degrees apart in their orbits. While it's difficult to explain the physics of this, it means that the gravitational pull of these large satellites balanced out all around the planet. (The stability of the water molecule, in which two hydrogen atoms are attached to a larger oxygen molecule in a similar layout, demonstrates the soundness of the design.)
This stable gravitational field supported a superatmospheric band of water around your planet. Reflected heat from your atmosphere, incoming heat from the sun, and the fact that it was always in motion (the water orbited your planet completely in less than an hour) kept it in liquid state. This served as a buffer, evening out the effects of the sun's warming rays on your atmosphere and preventing atmospheric disturbances. It also protected your planet from the most damaging rays generated by the sun. (A special gas concentrated at your planet's poles provided a lesser level of protection in an area where less was needed.)
If one of those moons could be destroyed this belt of water would immediately crash to the surface. There was enough to bury the land surface of your planet in over a mile of water, sufficient to drown everything not already designed to live in water, including all humans.
The disruption of the gravitational field around your planet would also generate dramatic changes in the surface of the planet. Its outer crust would be fractured into a number of plates which would float around on the molten core. These would never totally settle back into place after the catastrophe. It was this feature, I have been told, that generated the other cover-up ideas.
The boss felt sure (history has borne him out) that the survivors of your race would eventually develop an understanding of your world nearly equal to that your ancestors had. When you got that far you would see our "fingerprints" in the altered genetic codes. If we could get you to believe a well-crafted cover story, the boss suggested, you would attribute everything you saw to natural causes and our secrets would be safe.
The cover story was to involve billions of years of gradual natural change (you call it evolution). By the time you were smart enough to measure the movement of plates on your planet and deduce where they originally had belonged, the rate of their movement would have slowed so much that your calculations would show that the movement had taken millions, if not billions of years. That kind of time would make natural genetic changes of the sort already undertaken, possible on a natural basis.
Probably many of us were thinking, as I was, that natural genetic changes didn't often lead in the right directions. Left to its own, a planet like yours based on death and reproduction would suffer genetic deterioration, not improvement. We hadn't long to think like this, however, before the boss announced the most ingenious part of the plan our leaders had concocted.
Those harmful rays I've already mentioned would have several effects. Every once in a while one of the particle rays would impact a genetic molecule and change its code. With the water barrier gone, these "mutations" would be much more frequent. As we already knew, mutations that made an organism less able to survive would not be passed on for many generations. In the hunter and prey world we had "created," any mutation that enhanced a creature's chances of survival would, eventually, take over a population.
Of course, the boss announced, we did not intend to sit around waiting for chance mutations to move things in the direction we wanted. We didn't have that amount of time. But once we got you to believe that the world had been around for billions of years, your natural desire to be free of obligation to the master that made you would lead you to believe that the processes just described could account not only for the variety of species on your planet, but even for the very existence of life itself. Some of us didn't think you'd be that gullible, but time has again proven the boss right.
That massive increase in incoming harmful radiation I've already mentioned formed one more link in the boss's chain of deceptions. These particles could (and very often did) collide with or even merge with a molecule, creating an unstable form of that molecule. The instability would eventually right itself, sometimes in a matter of seconds or days, sometimes over hundreds or thousands of years.
At the right time, the boss announced, he would surreptitiously introduce the idea of measuring these unstable elements to determine the age of an object. (This is how we usually use the process you call "tempting.") Anything formed before the planned disaster would get dated millions or billions of years into the past. Those things formed afterwards would be dated with less and less "error" until concentrations of the unstable molecules reached stasis. This would happen, the boss theorized, long before you developed the capacity to use such sophisticated means of measuring your world.
Like I say, the plan demonstrated the superior intelligence of the boss, including such a masterful chain of deceptions in so simple an action. The only part of the cover story that necessitated our intervention involved the placement of carcasses in the multiple layers of sediment that would be laid down once the initial violence of the catastrophe had spent itself.
In order to convince you that the evolutionary process you would see in action around you could explain the origin of life, we would need to provide more evidence. We would do this by arranging the geologic record of the catastrophe to reflect a long, gradual progression of complexity.
As I've already noted, naturally occurring mutations occasionally produce some individuals that are better suited to surviving in a particular environment. But they always result in an organism with the same or less complexity -- never an individual with greater complexity. But if you saw a progression of organisms from simple to complex in the geologic record, the boss suggested, you would assume that greater complexity was possible.
These days we get a lot of amusement from attending debates you humans hold on the issue of evolution. Nobody on either side ever tells the truth, which demonstrates the power of the cover story the boss crafted. Those who believe the processes of mutation and survival of the fittest (what you call natural selection) have concrete evidence that these things happen. But it's also clear you have believed the fabricated evidence of radiometric dating and the fossil record.
Those who don't believe natural selection can explain the origin of life usually also end up denying some of the established facts about life on your planet, which makes it easy for their opponents to dismiss their arguments. And the hatred and animosity both sides exhibit toward the other demonstrates that we don't need to get involved in making you do evil things.
Back to the story. The crew assigned to convince some of you to destroy one of your moons succeeded quickly (it's so easy to plant suggestions in as weak a mind as yours). Somebody on your planet (prompted by the master, no doubt) built a large boat. We knew the structure, sturdy and well-designed as it was, couldn't withstand the forces that would break loose when the moon was blown to little bits. In fact, we dared to believe that humanity would be wiped out after all.
What surprised us most was when those of our race who had remained with the master began herding up land animals and leading them to the boat. Some of us tried to lead the species we had developed into the boat as well, but we were blocked. (Our sea creatures were still safe, of course.) The boss even assigned a squad to assure the destruction of the boat, but none of us really expected to succeed. It wasn't surprising when the squad returned, reporting that the master's agents had blocked them. I'm glad I wasn't assigned to that squad. The boss erupted into physically violent anger and nearly killed some of them.
Fortunately, there was plenty of work for everyone. It took nearly a year for us to ensure the correct placement of specimens in the sediments laid down as the rearrangement of outer crust plates caused areas of land to rise above the much deeper waters. (We may have missed a place or two, but we have learned that your scientists quite readily dismiss an occasional bit of evidence if it goes against the bulk of established knowledge.)
As already noted, all the land species we had developed were destroyed by the catastrophe. Those of us in the sea creature section were moved to the land animal section of the squad. Our job was to reintroduce as many of the modified creatures as the master's agents would allow. (The sea section did meet occasionally to be sure our creatures adapted to the rapidly increasing salinity of the major bodies of water on your planet.)