For the third time, there is a sunrise. This time, we aren't viewing the celestial bodies. Instead, the focus is on the awakening man-apes in the caves. Something has obviously gotten their attention. They are stirred up - growling and staring at something. We hear a choir of voices chanting. Finally, it is revealed. Sitting in front of the caves is a rectangular block. Sharp-edged and jet-black, this "monolith" just seems so weird and out of place. It contrasts the natural landscape around it. The man-apes have never seen anything remotely like it. Their curiosity finally overcomes their initial fear and they approach it slowly. They surround it and eventually one of them dares to touch it. The choir voices raise and eventually, all the man-apes in the group have surrounded the monolith and are reaching out and touching it. It's smooth stone or metal (you can't tell) must feel as alien to them as its appearance does. Just as the chorus peaks, we witness a new point of view, an alignment of the monolith, the Sun, and the Moon.
In Kubrick style, the scene, including the music, suddenly ends abruptly. We are again seeing the man-apes and the harsh landscape. Everything is back to normal. The morning incident seems to have been forgotten. We focus on one particular man-ape as he furiously digs in the never-ending quest for nourishment. Something grabs his attention. He looks up. We get a repeated glimpse of the shot of the monolith, Sun, and Moon. The hominid grabs a large bone and begins pounding the ground and other bones around him. We once again, hear Strauss' Thus Spake Zarathustra. At first, the man-ape seems confused as to why is he doing this. As he strikes the other bones, causing them to break and go flying, the man-ape gets more enthusiastic and his motions become more purposeful. He gets the point! The bone in his hand increases his power. With this first tool, he can kill tapirs. He and his cavemates suddenly have a new source of food.
For the third time, we start off a scene with the desert landscape. This time, we only see a solitary man-ape eating. He is not digging in the ground for roots and insects, he is eating fresh (tapir?) meat. We then see the clan in small groups all eating meat. All is well for a change.
This is a monumental scene of the film. We are introduced to the monolith. Its simple, yet perfect shape is perplexing to both the man-apes and the audience. Its black color and the way it sits there silently gives it an almost menacing appearance. There is a common misconception about the scene showing the "cosmic alignment". Some point out that the Sun had just rose so how could the Sun be directly overhead so quickly? Also, when the Sun and Moon are so close to each other in the sky, it is impossible to see the Moon due to glare from the Sun. One has to realize that the view of the "cosmic alignment" was for the audience only. Kubrick clues us in by revealing the monolith in alignment with the Sun and Moon. This is a reference to the alignment shown at the film's beginning. Obviously, the monolith is connected to whatever was shown visiting the Earth.
This re-asks the question of what came to Earth. The novel, which was adapted from an intermediate version of the screenplay, explains it as a very advanced alien intelligence, advanced so much that even 4 million years ago, they were way ahead of mankind today. Did Kubrick follow this part of the screenplay? The music we hear (Ligeti's Requiem For Soprano, Mezzo Soprano) features the chanting of a choir. While we don't quite hear "Hallelujah", it comes across as a religious piece. The monolith even looks like a religious symbol. The way it is planted into the ground is not dissimilar to a cross. The triple alignment also can be interpreted as the holy trinity. Of course, a third explanation can be that the monolith incident of 4 million years ago was the beginning of religion. The empowerment our ancestors received at the time of the monolith may have passed on through the generations leading humankind to associate power with an unknown higher form of life.
The highlight of this part of the story is when the solitary man-ape (Moonwatcher in the novel) learns to use an ordinary bone as a tool. Over and over, in other discussions I read and hear, this scene is usually mistakenly described as "the monolith teaches the hominid to use tools". This was not a class, it was a test. Look at Moonwatcher'a actions. He is searching for food, he suddenly glances back towards the monolith. He receives a command from as far as he is concerned, God. He lifts up a bone gingerly and begins to strike the other bones. His mannerisms at this point indicate unsure compliance, i.e. he was told to strike the bones but was not told why. People who complain that 2001 does not have good acting overlooked a great performance here. There is a moment where Moonwatcher suddenly realizes why he is striking the bones. He gets it. He passes the test. Once this happens, he strikes the bones with much more enthusiasm. He feels triumphant and the flashes of a dying tapir indicate he has made the important mental connection that the power he has in striking the dead bones would also apply to striking living things.
2001 features many tests of humankind. Although not shown in the film, it is logical to assume the "tool test" was not just given to this one particular group of man-apes. It is likely that most man-ape groups failed the test. The film shows us one of the rare cases of a success. Possibly, the rival tribe encountered the monolith and failed the test. This of course, falls right into evolution, the inferior tribe - that being the one that couldn't reach out and think beyond their normal scope, won't survive.
Thus Spake Zarathustra is played because passing the test was the moment in time where the man-apes became Nietzsche's "proto-man". Man-apes will no longer live on instinct, alone.
Notice how the man-apes appear more relaxed and sociable with one another once they have a healthy portion of food in them. Having leisure time will enable them to develop better communication skills. The path to humanity has begun.
Early versions of the screenplay and novel had a less mystical tone. Indeed, a ship lands and an alien comes out and teaches the man-apes to use bones as hunting tools and reeds to tie knots. This is where we see the difference between author Arthur C Clarke and director Stanley Kubrick. The physical alien would be typical of Clarke and would work in the story as a novel. Kubrick never wanted to make a typical science fiction film with "little green men" or some other physical manifestation of an extraterrestrial. It is because of Kubrick and his vision that I, and others, get to endlessly speculate this film.
Early versions of the monolith had it as a crystal pyramid, similar to the object in The Sentinel - the short story 2001 originated from. Director Stanley Kubrick decided that people might want to relate the monolith to the Egyptian pyramids, something Kubrick did not want. So they tried a crystalline rectangular block. Unfortunately, this didn't work either as there was no way to keep it from reflecting the studio lights. This resulted in a black monolith.