Ive just about finished the game (i.e. gotten to the last time period) and i think the strong points of the game have been covered by others, so id like to share some issues I had with the game.
1. The last third of the game takes forever. Ive spent a week leaving the game idling when i go shower/pee/whatever, as well as when i watch youtube videos, take a deep breath, etc. Even then, the last few levels are just ridiculous. Same goes for the level-up requirements, which similarly take way too long to achieve much of the time.
2. Too many of the elements are useless. Really, all you need is Oxygen, Nitrogen, Carbon, and Hydrogen to make most of the important elements.
3. The bonus molecules that would pop up didnt really help that much, even when I upgraded it. On the same note, grouping more than one extractor on an element helped very little
4. There's too much clicking to level up the natural selection thing. Near the end, i was clicking probably 100 times just to gain 1%. Its really obvious, and a bit sneaky, in my opinion, that you make the requirement to level up one percentage point grow almost exponentially every time another percentage point is gained.
5. This is a nitpick, but some sort of guide would be helpful, especially since your descriptions for molecules just link to wikipedia. I forgot, after week 3 of playing this game, of what the spinning yellow circle even did. It doesnt seem to increase effectiveness of extractors much, thats for sure.
I understand that this is an "idle game," but you seem to have focused too much on longevity. I guess that's important, for keeping users playing and all, and I understand that, but you took it too far in that direction. An idle game should have a feeling of constant progress that the player has a direct hand in, and while you do accomplish this, I still felt like I was grinding, just to get to the grinding (i.e., completing the level ups, so I could grind for the next life stage).
My suggestion would be to take it in a more academic direction. Make it so that the player is learning while playing the game, about different elements/molecules, as well as time periods. Lastly, loosen up the requirements for everything. As it is, the game drags on for about two weeks after it becomes tiresome.