Last Night's TV: It's only rock and holes - but I like it

Earth: The Power of the Planet, BBC2; Imagine BBC1

Earth: the Power of the Planet isn't so much a science documentary as an extended adventure holiday for its presenter, Dr Iain Stewart. In the course of the first episode, he abseiled into the mouth of an active volcano (only for extreme adrenalin junkies, this), scuba-dived into a tectonic seam in Iceland and whitewater rafted down a gorge in New Zealand. Apparently, "it's only when you're fighting the rapids that you can begin to understand how powerful the force of water can be", so we'll just have to take the latter as part of a hands-on research programme, rather than just a way to titillate a piece to camera. I don't know whether he's also the guy seen sky-surfing in the trail for next week's programme, but I'll be bloody impressed if he does a link while doing backward flips at 10,000 feet.

If you're allergic to the usual co-production bombast, all surging orchestral music and ridge-clipping helicopter shots, then this kind of frantic sexing-up will probably bring you out in hives. Dr Stewart himself barely utters a sentence without an exclamation mark attached to it, and the vocabulary of awe and wonder gets its familiar pounding, with words such as "extraordinary" and "wonderful" and "magnificent" coming round again and again, like rotating extras in a low-budget battle scene. That said, one can, for once, understand the anxiety. Earth: the Power of the Planet is about geology, so its subjects are not going to do anything cute, or eat one another in a dramatic way, or indulge in mating rituals. They're just going to sit there rockily, eroding at a rate that evades the time-lapse camera.

Except for volcanoes, of course, which gratifyingly unite the hard science of tectonics and plate subduction with the production aesthetics of a Jerry Bruckheimer movie. Hence the early visit to Erta Ale in the Afar region of Ethiopa, disappointingly unvolcano-like from the exterior, but cartoonishly satisfying inside, where a kettle of molten magma seethes and bubbles like something from The Simpsons. Dr Stewart's piece to camera didn't rise to the occasion, contenting itself with pure redundancy ("I'm standing on the edge of an active volcano right next to a pool of molten lava!"), but if his script was underpowered, Erta Ale certainly wasn't, offering a perfect model of plate tectonics in action, as plaques of cooled black lava scudded over the surface, tiny continents in motion. At a global level, the same process is still going on, and Earth: the Power of the Planet helpfully included a speeded-up prediction of general trends. Don't buy beach-front property in Florida if you're planning on a long-term investment, because in a couple of million years, it appears to bump into Namibia, where property prices aren't quite as buoyant.

"The cliche is that it's not a bubble till it bursts," said one of the talking heads in last night's Imagine..., How to Get On in the Art World, in which Alan Yentob reported on and contributed to a current boom in the contemporary art market by going shopping with 5,000 of his own money. This doesn't buy you a lot at the salesroom, as Yentob quickly found out. But when he visited the Frieze Art Fair in London, a kind of fine-art car-boot sale that now draws big dealers and big crowds, he fared rather better. The film began with a beginner's briefing on London's increasing centrality in the market for modern art, but perked up considerably when it became a buyer's guide, explaining the weird dynamics of a boom market where collectors are obliged to sell themselves to the dealers in order to get the more desirable pieces. Museums are top in the pecking order when it comes to purchases, because a museum acquisition will instantly add patina to a career. Serious collectors come second, because the dealer can at least be assured that his client's work will be keeping company with other A-list names, and the poor punter who wants something to look nice over the mantelpiece barely gets a look in. I would have quite liked an explanation of what kind of premium an attendant film crew and a job as the presenter of a BBC arts programme gives you, but that wasn't included in the explanation.

Yentob took advice from other collectors and an engagingly blunt art critic called Dave Hickey, who gives good interview. "The art over there, 98 per cent's shit, and that's about right," he said genially, "98 per cent of everything is shit." Yentob, hoping to put his finger on a bit of the 2 per cent that wasn't, eventually settled for a sculpture by a young British artist called Ryan Gander, which came in at a relatively reasonable 3,500. This seemed suspiciously low to me, given the prices he'd been quoted everywhere else, but perhaps he just got in at ground level. He bought it just in time, anyway: last week, Gander won a Paul Hamlyn Foundation Award, a prestigious prize that will bump up his prices whatever happens to the bubble.