TORONTO--In the past month, the apparent age of the first known animals nearly doubled to a startling 1.1 billion years, then swung back to the conventional figure of 600 million years. And last week at the annual meeting here of the Geological Society of America, the pendulum swung one more time, back toward the extraordinarily early dates claimed a month ago. Paleontologists may have to reckon after all with signs of animals 500 million years earlier than the first known animal fossils.
The first dramatic claim came in the 2 October issue of Science (pp. 19 and 80), when researchers said they had found tracks of multicellular animals in 1.1-billion-year-old Indian rocks. Then, paleontologist Rafat Jamal Azmi of the Wadia Institute of Himalayan Geology in Dehra Dun, India, claimed in the Journal of the Geological Society of India that he had found tiny fossils, known to be from about 540 million years ago, in rocks just above the purported trace fossils. If so, the tracks might actually be only about 600 million years old (Science, 23 October, pp. 601 and 627).
In a question-and-answer session at the meeting, however, paleontologist Nicholas Butterfield of the University of Cambridge reported that after Azmi visited and gave him a look at actual samples, he believes they are not fossils at all but artifacts. "They're absolutely not biogenic when seen in Technicolor" under a light microscope, Butterfield says. Once he could view the objects from any angle and under varied lighting, Butterfield concluded that their ribbed structure was simply a reflection of fine layers in the rock itself rather than the regular markings of a fossil.
Others also have doubts. Two other Cambridge experts in Cambrian fossils, Simon Conway Morris and Soren Jensen, studied the samples with Butterfield when Azmi visited Cambridge 2 weeks ago, and they agree that the bits are not fossils. Azmi, however, stands by his find, saying that Conway Morris studied unpublished fossils rather than the examples cited in his recent paper: "There cannot be any doubt that these are fossils, for they are not artifacts."