Page 55 - The Restless Earth Fossils

54 Fossils

where hot magma from Earth’s interior sizzles out of cracks on
ocean floors. Various species of such primitive Archaea live near
these vents today.
Stromatolites passed lots of gas—for hundreds of millions of
years. Ocean water absorbed all it could, but then oxygen leaked
into the air. After more hundreds of millions of years, many rocks
literally rusted, forming what geologists call banded iron for-
mations. The sky gradually changed colors, too, from the vomit
green of a methane and ammonia atmosphere to the familiar
blue, oxygen-nitrogen mix we see today.

the garden oF ediacara

Toward the end of the Proterozoic Eon (lower right forearm
on our human timeline—roughly 630 million years ago), living
things began forming colonies of cells that resembled transparent
air mattresses. Geologist Reg Sprigg first found evidence of these
creatures, called Ediacarans, in the Flinders Ranges of southern
Australia in the 1940s. A schoolboy by the name of Roger Mason
found another Ediacaran in an English quarry in the late 1950s.
Scientists later discovered similar fossils in the ancient rocks of
Russia, Canada, and Namibia. The Ediacarans display various
shapes, but they seem to have no front and rear ends. These “gut-
less wonders” may have survived by exchanging nutrients and
wastes with seawater and perhaps forming symbiotic associations
with cells that could photosynthesize.
About 100 million years later, another revolution took place—
one that banished stromatolites to far corners of our modern
world like Shark Bay, Australia, and wiped out the Ediacarans.
Predators brought their jaws and other weapons into the food
chain. The evolution of new forms slipped into a higher gear and
began the Paleozoic Era (which covers, in our time line, the palm
of your right hand). Let us examine some firsts in the history
of life and see where to find the fossils that reveal the once-lost
worlds of prehistory.

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