Read the passage carefully and answer the following questions:

Diamonds are formed deep within the Earth about 100 miles or so below the surface in the upper mantle. Obviously, in that part of the Earth, it's very hot. There's a lot of pressure, the weight of the overlying rock bearing down, so that combination of high temperature and high pressure is what's necessary to grow diamond crystals in the Earth. As far as we know, all diamonds that formed in the Earth formed under those kinds of conditions and, of course, that's a part of the Earth we can't directly sample. We don't have any way of drilling to that depth or any other way of travelling down to the upper mantle of the Earth. The diamonds that we see at the surface are ones then that are brought to the surface by a very deep-seated volcanic eruption. It's a very special kind of eruption, thought to be quite violent, that occurred a long time ago in the Earth's history. We haven't seen such eruptions in recent times. They were probably at a time when the earth was hotter, and that's probably why those eruptions were more deeply rooted. These eruptions then carried the already-formed diamonds from the upper mantle to the surface of the Earth. When the eruption reached the surface it built up a mound of volcanic material that eventually cooled, and the diamonds are contained within that. These are the so-called Kimberlites that are typically the sources of many of the world's mined diamonds.

One of the things we know, therefore, about any diamonds that were brought to the surface is that the process of the Kimberlite eruption bringing the diamonds from the upper mantle to the surface of the Earth had to happen very quickly, because if they were travelling too long and too slowly they would have literally turned into graphite along the way. Once the diamonds are brought to the surface and cooled relatively quickly, those carbon atoms are locked into place and there's just not enough energy to now start rearranging them into graphite.