The first monolith appears on Earth some 50,000 years ago... Or so we are led to believe as humans are still ape like creatures and we see that one is killed by a saber tooth tiger. The monolith promotes the evolution (dawn) of man, which takes an undetermined, but lengthy amount of time.

Fast forward to finding the monolith on the moon. Dave touches it and... what? From what I can tell, nothing happens.

I don't remember him ever seeing the 3rd monolith around Saturn.

When he touches the 4th monolith, he evolves into the star child.

But what, if anything, did the 2nd monolith on the moon do?

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    "I don't remember him ever seeing the 3rd monolith around Saturn." Isn't that the "It's full of stars" moment? My understanding is that the third monolith transported Dave to the place where he could be transformed. Commented May 3, 2016 at 21:05
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    "Fast forward to finding the monolith on the moon. Dave touches it..." That wasn't Dave Bowman. That was Heywood Floyd. Commented May 4, 2016 at 5:43
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    IIRC There were only three monoliths - but note that the (first) movie and book have different locations for the third, as discussed in the question Why is the destination of the Discovery in 2001: A Space Odyssey Saturn in the book and Jupiter in the movie? (Saturn in the book, Jupiter in the movie basically since Saturn's rings couldn't be visualised convincingly. Clarke talks about this in 2010's foreword and decided to also use Jupiter as the final destination there)
    – Zommuter
    Commented May 4, 2016 at 6:35
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    very related: What did the black monoliths do in 2001: A Space Odyssey?
    – Zommuter
    Commented May 4, 2016 at 6:35
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    The second monolith extends the running time of the film. Commented Feb 16, 2017 at 16:34

3 Answers 3


This is discussed (at length) in the accompanying book. In short, the second monolith was an alarm device intended to show that the apes on the planet below had evolved to the point that they were able to reach their nearest planetary neighbour and to perform basic survey tasks. That being the case, it would now be of benefit for the monolith-builders to activate phase II of their plans, creating a second sun in the solar system to allow colonisation of the moons of Jupiter.

"Piecing things together after the event, we decided that the monolith was some kind of Sun-powered, or at least Sun-triggered, signaling device. The fact that it emitted its pulse immediately after sunrise, when it was exposed to daylight for the first time in three million years, could hardly be a coincidence.

"Yet the thing had been deliberately buried - there's no doubt about that. An excavation thirty feet deep had been made, the block had been placed at the bottom of it, and the hole carefully filled.

"You may wonder how we discovered it in the first place. Well, the object was easy - suspiciously easy - to find. It had a powerful magnetic field, so that it stood out like a sore thumb as soon as we started to conduct low-level orbital surveys.

"But why bury a Sun-powered device thirty feet underground? We've examined dozens of theories, though we realize that it may be completely impossible to understand the motives of creatures three million years in advance of us.
  "The favorite theory is the simplest, and the most logical. It is also the most disturbing.

"You hide a Sun-powered device in darkness - only if you want to know when it is brought out into the light. In other words, the monolith may be some kind of alarm. And we have triggered it.

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    I don't think the plan to create a second sun came about until after Starchild Bowman returned to Jupiter and saw Europa's life forms in 2010. I think TMA-1's purpose was to point whatever civilization happened upon it to the monolith orbiting Jupiter/Saturn, which -- having established that this civilization was capable of sub-light space travel -- would then kidnap an individual and turn them into a Starchild.
    – Gaurav
    Commented May 3, 2016 at 22:06
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    I think it's worth noting that this "solar-powered alarm", to be activated once humans were capable of digging it up, was one of the very first concepts from 2001 that Clarke conceived of. A nearly identical scenario is the premise of his short story The Sentinel, published decades earlier.
    – recognizer
    Commented May 3, 2016 at 22:33
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    "having established that this civilization was capable of sub-light space travel" - yeah, but that was true when they reached the moon. On the time scales we're talking about, there's pretty much zero difference between the race that reaches the Moon and the one that reaches Jupiter. It really doesn't make sense in that respect, and I suspect was driven entirely by the desire to have a deep space trip in the plot. Commented Mar 8, 2017 at 2:25

The second monolith was a beacon that signaled the civilization that created it that humanity had reached the Moon. The first monolith kickstarted humanity's evolution from simple primates, while the second one was monitoring when they became a space faring race which marked them ready for the next part of the grand plan.

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    This. The second monolith starts sending a signal the moment sunlight hits it, meaning that Man has reached the Moon, found the monolith, and dug it up. The signal points to the third monolith near Jupiter (Saturn in the novel). Commented May 3, 2016 at 17:48
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    It's been a long time since I read the books, but if I recall correctly it was implied that the monoliths were acting independently of the civilization that created it. I don't think it was ever stated one way or another that they would signal their creators. The signal we did get to know about was the one that was sent to the monolith near Saturn/Jupiter.
    – JBentley
    Commented May 4, 2016 at 20:32

Just like the first monolith triggered apes learning to kill, the second monolith triggered the evolution of computers learning to kill.

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    Why do you think so? Do you have evidence to back this up? Commented Feb 16, 2017 at 14:23
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    The book establishes that the apes already knew how to kill.
    – jwodder
    Commented Feb 16, 2017 at 18:14

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