Last Night's TV: 9/11: The Fireman's Story/Channel 4<br />Horizon/BBC2

Turns out there has been something of a conspiracy regarding 9/11, though it's not one that's likely to satisfy the delusional, and it may indeed present something of a problem for one of their cherished narratives. I shouldn't really use the word "conspiracy", though, given the excitable nature of "truthers". It's really more in the nature of a circumspection about how much we've been shown of what was recorded on that day, and it was revealed (to my knowledge for the first time on television) in 9/11: the Fireman's Story. The programme itself was a pretty straightforward exercise in commemoration and reminiscence. But in a couple of respects, it pushed the boundaries. It included footage of people jumping from the towers and it also alluded to what the first responders encountered as they arrived. A single brief shot of what looked like bloody rags in the street was what you saw – an ambiguous clip that was then horribly focused by the memories of a fireman who'd driven one of the appliances on that day and had found himself trying to steer round body parts in the street. In the end, he'd been forced to give up. "Forgive me," he recalled saying, and then he just drove over them.

Even without that charnel-house detail, the fireman who responded to the attack on the towers knew they were facing an enormity. "It felt like it was raining people," said another contributor to the film. "I hear this whistle coming, just like a bomb," he said, recalling the moment that a falling body hit one of his colleagues, killing him instantly (he was the first fireman to die in the attacks). Others still live with what they saw on the ground, like the firefighter who found a man in a brown suit lying on the pavement in a pool eight foot wide: "Everything that had been inside him was outside him," he said, his face grey even in the retelling. And one assumes that all the cameramen who raced to the scene that day simply pointed their cameras elsewhere, or that decorum has always edited this stuff out.

9/11: the Fireman's Story was partly an exercise in heroic myth, consolidating the sense of how brave these men were, as they ran towards a fire they knew was far beyond their powers of control. But it also intriguingly explained the origin of the New York Fire Department's characteristic aggression. Where some other services contain fires, they tended to take them on (the likelihood of dying on the job was reportedly eight times higher than in the London Fire Brigade), a legacy of their beginnings in the gangs of New York, when fire crews were made up of local amateurs and would sometimes fight rival teams for the honour of putting out a blaze. A longstanding rivalry with the New York police (which also had its roots in those outlaw beginnings) had possibly aggravated the losses on that day too. Though a police helicopter issued several warnings about the state of the second tower to fall, the fire service were on a different radio network and didn't get them. What's more the intimacy of the fire service – in which fathers and sons and brothers worked alongside each other – made the losses all the more devastating. One of the contributors here, Chief Pfeiffer, has to live with the fact that he ordered his own brother up into the North Tower. He never saw him again.

It's become safe to watch Horizon again, or at least you can now be reasonably confident that it won't induce apoplexy if you have a low tolerance for spurious thrills and dumbing down. Last night's programme was about the Earth's core – a lot closer to us than the moon but certainly less accessible. Even the deepest laboratory in the world – somewhere in South Dakota – will only take a scientist 0.02 per cent of the distance to the centre, and beyond that things get unworkable. Fortunately, scientists have been quite ingenious in taking the planet's pulse by other means, principally seismic (Yay! We can show an explosion!) though another gratifyingly hazardous experiment involved filling a giant spherical kettle with molten sodium and whirling it round at very high speeds, to create a miniature model of the Earth's internal convection currents. The bullet points were these: there's a liquid core of incandescent iron at the centre of the Earth inside which is a solid core roughly the size of the moon, composed of giant metallic crystals. Oh, and it's entirely possible that the magnetic poles will flip around at some point in the next 10,000 years. Come to think of it, this was a bit more disaster movie than some recent episodes, but take it from me, it's got a lot better.