Final answer:
The most extensive rift on the earth's surface marked by a chain of steep-sided lakes and volcanoes is the Great Rift Valley.
Step-by-step explanation:
The most extensive rift on the earth's surface marked by a chain of steep-sided lakes and volcanoes is the Great Rift Valley. The Great Rift Valley in East Africa is divided into the Western Rift and the Eastern Rift. The Western Rift runs along the border with the Congo. On the western edge of the Western Rift are the highlands, which have a series of high-elevation mountain ranges, including the Rwenzori Mountains. The Eastern Rift is a wide basin with shallow lakes that do not have outlets.