Calymmian Period
Breakup of Columbia Super-continent
The Calymmian is the first period of the Mesoproterozoic, occuring after the (Statherian) Paleoproterozoic, and before the Ectasian Period
Geologic Age
1,600–1,400 Ma
Greek word for "cover", indicating the expansion of "platform covers", which are layers of igneous or sedimentary rock that accumulate over cratons
Eon / Era
What happened during this time?
Geological
A time of continent building, where the Earth's crust thickens due to the deposition of rock on top of older rock.
Continental plates expand as sediments are washed into the sea and deposited along the coast, making the sea shallower.
Movement of continents also creates shallow seas between landmasses, which are also gradually filled up due to the deposition of sediment, forming new land.
Breakup of the super-continent Columbia
Began around 1.6 billion years ago, and continued through the Calymmian to end in the Ectasian, around 1.3-1.2 billion years ago.
Rifts appeared along the western margin of Laurentia (the north American plate), the east margin of India, southern margin of Baltica, southeastern margin of Siberia, northwestern margin of South Africa, and the northern margin of the South China Block.
Rifting was accompanied by volcanism along the rift sites, which led to large igneous deposits of rock in these regions.
Biological
Eukaryotic super-groups probably already diverged by early Mesoproterozoic time
Leiosphaeridia is another globe-shaped organism, ~70 μm wide, which has wall features that may indicate that it is a representative of the green algae [Javaux et al., 2004]
Possible eukaryote fossil, Tappania plana, from 1,430 Ma of the Wynniatt Formation, Victoria Island, northwestern Canada (Javaux et al., 2001; see also Javaux et al., 2003)
Structurally complex microfossils with irregularly branching and bulbous protrusions; morphology suggests the presence of a cytoskeleton: character unique to eukaryotes
Analysis of Tappania morphology shows it to have been an actively growing, benthic, multicellular organism capable of substantial differentiation (Butterfield 2005)
Most notably, its septate, branching, filamentous processes were capable of secondary fusion, a synapomorphy of the "higher fungi"
Combined with phylogenetic, taphonomic and functional morphologic evidence, such "hyphal fusion" identifies Tappania reliably, if not conclusively, as a fungus, probably a sister group to the "higher fungi," but more derived than the zygomycetes.
Other Proterozoic acritarchs exhibit fungus-like characteristics (e.g., Trachyhystrichosphaera, Shuiyousphaeridium, Dictyosphaera, Foliomorpha), indiciating that there is evidence for an extended and relatively diverse record of Proterozoic fungi.
Horodyskia is a fossilized organism dated from 1,500 - 900 mya, described as a "string of beads" connected by a very fine thread (Yochelson & Fedonkin 2000, Fedonkin & Yochelson 2002).
This organism may have been an early metazoan (Fedonkin 2003) or possibly a colonial foraminiferan (Dong et al 2008)
Above: Tappania plana
Below: Reconstruction of Horodyskia
Above: A putative green algae acritarch named Leiosphaeridia