Answer:
The rift valley formed when the crust pulled apart.
Step-by-step explanation:
The Great Rift Valley in Africa is a rift valley that stretches across the eastern part of the continent, though regionally it passes through Eastern, Central, and South Africa. It is the longest rift valley in the world, and it is constantly becoming wider and wider. To not be confused, this rift valley is not just one line cutting through the continent, but it has divisions that are connected to it.
The reason for the formation of the Great Rift Valley is the divergent boundary that has formed in this part. This divergent boundary has cracked open the crust of the African plate, now dividing it into two separate plates, the Nubian plate, and the Somali plate. Now, these two plates are moving away from each other, and over time, as the gap between them grows, the seawater will fill in the space between them, physically separate them, and give rise to a new sea which will later become an ocean.