If our extinction proceeds slowly enough to allow a moment of horrified realization, the doers of the deed will likely be quite taken aback on realizing that they have actually destroyed the world. Therefore I suggest that if the Earth is destroyed, it will probably be by mistake.
If you want to maximize your expected utility, you try to save the world and the future of intergalactic civilization instead of donating your money to the society for curing rare diseases and cute puppies.
If I could create a world where people lived forever, or at the very least a few billion years, I would do so. I don't think humanity will always be stuck in the awkward stage we now occupy, when we are smart enough to create enormous problems for ourselves, but not quite smart enough to solve them.
When you think of intelligence, don't think of a college professor; think of human beings as opposed to chimpanzees. If you don't have human intelligence, you're not even in the game.
An anthropologist will not excitedly report of a newly discovered tribe: 'They eat food! They breathe air! They use tools! They tell each other stories!' We humans forget how alike we are, living in a world that only reminds us of our differences.
My successes already accomplished have mostly been taking existing science and getting people to apply it in their everyday lives.
Let the winds of evidence blow you about as though you are a leaf, with no direction of your own. Beware lest you fight a rearguard retreat against the evidence, grudgingly conceding each foot of ground only when forced, feeling cheated. Surrender to the truth as quickly as you can.
The purest case of an intelligence explosion would be an Artificial Intelligence rewriting its own source code. The key idea is that if you can improve intelligence even a little, the process accelerates. It's a tipping point. Like trying to balance a pen on one end - as soon as it tilts even a little, it quickly falls the rest of the way.
The obvious choice isn't always the best choice, but sometimes, by golly, it is. I don't stop looking as soon I find an obvious answer, but if I go on looking, and the obvious-seeming answer still seems obvious, I don't feel guilty about keeping it.
Anything that could give rise to smarter-than-human intelligence - in the form of Artificial Intelligence, brain-computer interfaces, or neuroscience-based human intelligence enhancement - wins hands down beyond contest as doing the most to change the world. Nothing else is even in the same league.
A burning itch to know is higher than a solemn vow to pursue truth. To feel the burning itch of curiosity requires both that you be ignorant, and that you desire to relinquish your ignorance.
Textbook science is beautiful! Textbook science is comprehensible, unlike mere fascinating words that can never be truly beautiful. Elementary science textbooks describe simple theories, and simplicity is the core of scientific beauty. Fascinating words have no power, nor yet any meaning, without the math.
I don't care where I live, so long as there's a roof to keep the rain off my books, and high-speed Internet access.
You cannot 'rationalize' what is not rational to begin with - as if lying were called 'truthization.' There is no way to obtain more truth for a proposition by bribery, flattery, or the most passionate argument - you can make more people believe the proposition, but you cannot make it more true.
A scientist worthy of a lab coat should be able to make original discoveries while wearing a clown suit, or give a lecture in a high squeaky voice from inhaling helium. It is written nowhere in the math of probability theory that one may have no fun.
Since the rise of Homo sapiens, human beings have been the smartest minds around. But very shortly - on a historical scale, that is - we can expect technology to break the upper bound on intelligence that has held for the last few tens of thousands of years.