"Ring" cirrus cloud

I've taken to paying special attention to the clouds directly above. Doing so, there are many cirrus clouds that have this "Ring" feature to them. It is only noticed from below. Cirrus clouds that are distant all look flat and relatively featureless.

This cloud was fresh. The edges and features were well defined. As I watched it for a few minutes, the cloud dissipated and it's features smoothed out.

Some scientists are saying that cirrus clouds are created by blocks of ice/snow as big as four bedroom houses and these are what has filled up our oceans. Seeing a structure like this in a cirrus cloud, it isn't hard to imagine a block of ice entering the atmosphere, becoming heated, and explode, with the smaller and lower parts being blown off by the wind. You can observe for yourself.