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Cold death questioned for early algae.

Cold death questioned for early algae

During the last few centuries, the vast early portion of Earth's history has dwelled in relative scientific obscurity while geologists and paleontologists have trained their hammers on the more accessible rocks of the most recent ages. This early period, called Precambrian time, runs from the planet's birth around 4.6 billion years ago to 570 million years ago, which is about the time when animals with skeletons started to appear.

Despite its traditional obscurity, the ancient rocks of the Precambrian have started to yield secrets concerning this unsung portion of the geologic record. In the latest such news, two Australian paleontologists report the discovery of an incredibly rich collection of tiny algae fossils from the last part of the Precambrian.

In the Feb. 16 NATURE, Wen-Long Zang from the Australian National University and Malcolm R. Walter from the Bureau of Mineral Resources in Canberra, Australia, describe a large collection of microfossils found in 600- to 650-million-year-old rocks in central Australia's Pertatataka formation. Called acritarchs, these fossils are the spherical cysts, or cell walls, of tiny algae that lived at the time. In the Australian rocks, Zang and Walter have identified many new types of acritarchs that are both relatively large and complex in shape. With widths of 0.2 to 0.4 millimeter, these fossils bear ornaments like spikes and flanges that protrude from their spherical surface.

Andrew H. Knoll at Harvard University says the Pertatataka find is the richest of its kind, revealing that a diverse community of planktonic algae thrived at the time. The discovery will help scientists trace a wave of extinctions that killed off the large, lavishly shaped acritarchs near the end of the Precambrian. some researchers have proposed that a series of ancient ice ages wiped out these forms of algae. However, the Pertatataka community shows that acritarchs survived the ice ages, and thus must have disappeared at a later time for different reasons.
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Title Annotation:algae fossils found in Precambrian rocks
Publication:Science News
Date:Feb 25, 1989
Words:325
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