Phanerozoic aeon, also known as the Phanerozoic era, is a geological time period that started around 541 million years ago and continues to the present day, marked by the appearance of complex multicellular life. Synonyms for this term include the "Eon of Visible Life" or the "Era of Abundant Life." It is also referred to as the "Age of Animals" as it is characterized by the diversification and evolution of animal life. Further synonyms include the "Recent Era" and the "Cenozoic Era," a period within Phanerozoic aeon that only includes the last 66 million years and is marked by the evolution of modern life forms.