LIFE × EVOLUTION
The First Life Visible to the Eye
~1.56 billion years ago
Proterozoic · Mesoproterozoic · Calymmian
Sea organisms the size of a hand lived in North China about 1.56 billion years ago, a billion years before the Cambrian period, and are preserved as films of carbon.
The Gaoyuzhuang fossils are the remains of sea organisms that reached the size of a hand a billion years before the Cambrian, the geological period in which most animal groups appear as fossils. They come from the Gaoyuzhuang Formation, a body of rock layers in North China. They are carbon compressions, that is, fossils preserved as a film of carbon left by a flattened body. The forms are flat, some strap-shaped and some lance-shaped, up to 30 centimetres long and nearly 8 wide. Their outlines are regular enough for researchers to sort them into a few defined shapes. Fragments buried in the same beds show cells about ten microns across, a micron being a thousandth of a millimetre, packed edge to edge in a thick sheet. This arrangement indicates cells built into a single body and not an aggregation of independent cells.
Why it matters
A body the size of a hand requires more than a large number of cells. It requires a form repeated from one individual to the next and a rule of growth. The Gaoyuzhuang organisms had both a billion years before animals put them to use.
Dating & uncertainty
The two ages of these fossils come from two sections, a section being a place where the succession of rock layers is exposed. The 1.56 billion years shown for this entry comes from the section where the fossils were first described. In the Qianxi section, Chen and colleagues (2024) dated a volcanic ash eleven metres above the fossil bed at 1,588.8 million years, to within 6.5 million years. This newer measurement gives the older age. Its authors attribute the difference to the formation not being of one age from one section to the next, and do not present it as a correction of the date. The position of these organisms in the eukaryotic tree, the family tree of organisms with complex cells, is undetermined. The evidence establishes only that the cells are arranged in a sheet and that the organism was probably photosynthetic.
Earth history as one day
15:45:118 h 15 min before midnight
if Earth’s 4.54 billion years were compressed into a single day