Step-by-step explanation:
The Cambrian period is the period on the geological time scale which happened around 550 to 500 million years ago.
Before the Cambrian period, the Earth was dominated by the anaerobic prokaryotes as the Earth did not have the oxygen gas. Somehow, the photosynthetic bacteria started producing oxygen gas by the process of oxygen which got accumulated in the atmosphere of the Earth.
Due to this accumulation of oxygen, about 75% of the diversity at that time got eliminated and the new diversity of the organisms evolved which could utilize the oxygen gas.
This oxygen utilizing organism later diversified into a variety of the large organisms called the animals. These animals stabilized the ecosystem as plants produced oxygen absorbed by animals and animals produced oxygen absorbed by the plants. Both the animals and plants flourished during this time and diversified called the Cambrian explosion.
The evolution of oxygen and utilization of this oxygen is the main factor which led to the Cambrian explosion.