The earliest known manifestations of the geologic record of the Australian continent are 4.4-billion-year-old detrital grains of zircon in metasedimentary rocks that were deposited from 3.7 to 3.3 billion years ago. Based on that and other findings, the Precambrian rocks in Australia have been determined to range in age from about 3.7 billion to 541 million years (i.e., to the end of Precambrian time). They are succeeded by rocks of the Paleozoic Era, which extended to about 252 million years ago; of the Mesozoic Era, which lasted until about 66 million years ago; and of the Cenozoic Era, the past ...(100 of 51163 words)