Final answer:
Nearly all existing animal lineages evolved during the Cambrian period, which is renowned for the 'Cambrian explosion' of diversity and complexity in animal species. This period was a time of significant evolutionary development, outpacing the advancements seen in previous periods such as the Ediacaran and Cryogenian. Option 3 is correct answer.
Step-by-step explanation:
The Cambrian Explosion: A Major Evolutionary Milestone
The question touches on a significant event in Earth's biological history, specifically the diversification of animal life. The period in question saw the most rapid documented diversification and evolution of animal species, an event known as the Cambrian explosion. This pivotal phase took place during the Cambrian period of the Paleozoic Era, which dates back approximately 541 to 485 million years ago.
Prior to the Cambrian, the Ediacaran and Cryogenian periods featured some larger and more complex life forms compared to earlier times, but they pale in significance to the sheer diversity and complexity of the life forms that emerged during the Cambrian explosion. It was then that most extant animal phyla, including ancestors of modern-day echinoderms, mollusks, worms, arthropods, and chordates, came into existence. The Cambrian period's fauna included top predators like Anomalocaris, signaling the appearance of complex ecosystems.
The notable jump in animal diversity during the Cambrian has been corroborated by both fossil records and molecular evidence, making it a focus of much scientific study and debate. Preceding the Cambrian, the Ediacaran period hosted primitive animal life, termed Ediacaran biota, which are believed to have evolved from protists. Hence, while recognizing the significance of early animal life forms, the majority of animal lineages known today indeed have their roots in the Cambrian period's evolutionary burst.
The final answer to the question is: 3) Cambrian.