What is the lecture mainly about? [originaltext] Listen to part of the lectur

Listen to part of the lecture in an earth science class.
    Professor:
    OK, now, we know the earth’s surface, the crust is made up of tectonic plates. and These huge slabs of rocky crusts are slowly sliding over or under or past each other, and we said that most of the world’s volcanoes occur at the boundaries of these tectonic plates, where you have hot molten rocks squeezing up through gaps between the plates. But some volcanoes occurred not at the edges, but in the middle of a continental or oceanic plate, the Hawaiian islands, for example, are thousands of kilometers away from any plate boundaries.
    Yet you have vast amounts of magma, molten rock, or lava, flowing up through the earth’s crust, which means of course that the volcanic activity there can’t be explained simply by plate tectonics. So, how do we explain these volcanic anomalies? These exceptions to the general rule. Well, back in 1963. A geophysicist by the name of Wilson came up with the hot spot theory to explain how this particular type of volcanic activity can occur. And can go on for maybe tens or even hundreds of millions of years.
    Wilson’s theory was that hot spots exist below tectonic plates, and They’re the cause of these volcanoes. But what causes the hot spots? Well, the most popular theory that’s been proposed is the plume hypothesis. According to the hypothesis plumes, basically, columns of extremely hot magma well up from deep inside the planet’s interior, maybe even as deep as its core, and rise all the way up to melt through the earth’s crust.
    Now imagine a burning candle and imagine moving a sheet of heavy paper slowly over the flame of the candle. You’re gonna get a series of burned spots in the paper. Well, that’s just what’s happening with the Hawaiian islands. But instead of a sheet of paper, you’ve got a tectonic plate, and it’s moving over this plume of intensely hot magma. And rather than a series of burned spots in the paper, you’re getting a chain of volcanic islands where the hot plume melts through the crust under the Pacific Ocean.At one point after another, with active volcanoes, on the younger islands that are now just above the plume. And the other islands will the further away from the plume they are, now the older they are. And the longer ago, their volcanoes went dormant or extinct.
    Incidentally, volcanic islands may seem small, but the island known as Big Island, Hawaii, is one of the tallest topographic features on the planet, more than 5 kilometers from the sea floor to the ocean surface. And almost that much again, up to its highest peek. That’s nearly 10 kilometers from ocean floor to the highest on the island, which makes it taller.
    Even then Mount Everest, so you can imagine the huge amount of magma or lava that have flowed up to form even just this one island, much less the whole chain of islands. The plume hypothesis provides a pretty elegant explanation for a volcanic anomaly, like the Hawaiian islands. But while it hypothetically attractive, there’s very little direct evidence to support the theory, because so far, no one’s been able to actually observe what’s happening that far beneath the earth’s crust. Some studies have been done. Seismographic geochemical where the data is consistent with the model. But they aren’t a thin of a proof.
    Even the model supporters are uncomfortable claiming that the theory explains every volcanic anomaly, and like any popular theory. I suppose it has some determined critics. These critics have put forth a number of alternative theories. All I’m proven so far. But one well regarded theory is the crack hypothesis, which assumes that hot spots are created when a piece of the crust gets stretched, thinner, and thinner. And the resulting stress causes small cracks to open up at weak spots in the crust, and It’s through these cracks that magma pushes up to form volcanoes.
    Proponents of the crack hypothesis considers this a widespread phenomenon and believes that magmas not coming up from deep within the earth’s interior, but rather from just beneath the surface crust. This hypothesis is attractive because it fits with what we already know about Plato tonics, and It fits with what we know about some secondary, smaller hotspots. But how well does it explain the Hawaii in islands? Could a series of random cracks produce that same particular string of islands that sequenced so neatly from old to young? you know it worries me when a theory depends on coincidence to produce results.