Answer:
Animals on Earth
Step-by-step explanation:
The Cambrian explosion is referred to an event which took place in the past around 530 million years ago on the Earth.
Since the event took place in the Cambrian period of the geological time scale and lead to the evolution of the diverse forms of life or organism on Earth which looked like an explosion of the species on Earth, therefore, called the Cambrian explosion.
The Explosion took place due to the evolution of a new gas called the oxygen during this period by the green bacteria which led to the formation of the diversity of animals on Earth which could absorb the Oxygen.
Thus, the first animal on Earth is correct.