"The Star formation rate in the region before our Solar System formed was ~4-5 times higher than the galactic average."-Emilie T. Dunham

Maybe you have heard that it's hard to see the Milky Way from inside it? It's true, and since it is, what are the many things that we would like to know, that we have a hard time seeing? Frankly astronomy isn't very helpful in these kinds of cases. What do geologists fall back on when they really want to settle their arguments? Isotopes and a mass spectrometer. Specifically, Beryllium, Boron, Magnesium and Aluminum isotopes. 

We don't get a lot of good lectures about galaxy formation, and this one lays it out quite simply.

• Slide at 3:45 is not the Milky Way, but the slide is meant to demonstrate that star formation is more likely to happen in the arms of a spiral galaxy rather than some space between or around them. But at what rate?
• Slide at 6:55 is a standard periodic table you may have seen already, but now you have context beyond the gee-wiz factor. Note that Beryllium and Boron are exclusively formed by fission of something bigger. What bigger? Could be a lot of things that divide down to H, He, Li, Bo, & B. The process is detailed on the slide at 8:00.
• At 21:50 she does something similar with isotopes of Beryllium and Boron, though with a twist, the half-lives involved are quite different.
• She brings it all together at 44:30, with a slide that implies the scale of change the Milky Way may have undergone.
• Summary at 48:25.

None of the math and chemistry in this lecture is particularity difficult if and only if, you have some college education in chemistry. However if you don't, what you are looking at is a lot of natural fission. Natural fission involves an element degrade to a different/lighter element, which on average, takes a predictable amount of time. Since she has time, all she needs is space. The element tells you how far it could have come from per that periodic table at 6:55. Be & B could have come from anywhere but Al and Mg for sure came from a point in space that was massive (there was a lot of it,) and energetic (big explody.) So a place in space that had a lot of dust, turned into a big star then later, then left that place in a hurry. In this way she can predict where old nebulae were, how big they were, and where they distributed their stuff on explody.

Now she knows when and relatively where (in our arm of the Milky Way), a thing in the Galaxy happened, as well as the rate of happenings.