This reconciliation supports an evolutionary-developmental model connecting plant origins to freshwater green algae, or charophyte algae. The “evo-devo” model posits a more nuanced understanding of plant evolution over time, from simple cell division to initial embryonic stages, rather than large jumps from one species to another.
The microfossils are from the Lower Ordovician Period, approximately 480 million years ago and are direct evidence of the evolutionary assembly of the plant regulatory and developmental genome. This process starts with the evolution of the plant spore and leads to the origin of plant tissues, organs, and eventually macroscopic, complete plants – perhaps somewhat akin to mosses living today.
The scholars set out to describe an assemblage of spore-like microfossils from a deposit dating to the Early Ordovician age - approximately 480 million years ago. This material fills in a gap of approximately 25 million years in the fossil spore record, linking well-accepted younger plant spores to older more problematic forms. The team examined populations of fossil spores extracted from a rock core drilled in 1958 in northern Western Australia. These microfossils are composed of highly resistant organic compounds in their cell walls that can structurally survive burial and lithification using standard optical light microscopy.
What does it all mean? Molecular biologists also look at evolutionary history through time by using genes from living plants to estimate the timing of plant origins using “molecular clocks” -- a measurement of evolutionary divergence based on the average rate during which mutations accumulate in a species’ genome. However, there are huge discrepancies, up to tens of millions of years, between direct fossil data and molecular clock dates. In addition, there are similar time gaps between the oldest spores and when actual whole plants first occur.