LIFE
The Oldest Reef, Built by Microbes
~3.43 billion years ago
Archean · Paleoarchean
In Western Australia, a carbonate platform kilometres across preserves mounds, cones and wavy sheets raised by microbial mats as they trapped passing sediment. Seven distinct shapes recur across the platform, each in its own zone, arranged along the ancient shoreline much as living mats sort themselves by water depth. It is a reef, and nothing but microbes built it.
Why it matters
What survives here is not a single cell but a whole ecosystem, mapped across its landscape: the earliest picture we have of life already in business rather than just beginning.
Dating & uncertainty
Layered mounds can also be built by chemistry alone, which is why every claim this old is contested. Here the argument rests first on scale: seven distinct shapes, each keeping to its own zone across a platform kilometres wide, a pattern that in similar settings throughout Earth's history reflects the presence of organisms. Under the microscope, organic layers and traces of the original texture that change with the shape of each mound have since added a finer-grained case for the mats.
Sources
- Allwood et al. (2006), Nature · Stromatolite reef from the Early Archaean era of Australia
- Allwood et al. (2007), Precambrian Research · 3.43 billion-year-old stromatolite reef from the Pilbara Craton of Western Australia
- Allwood et al. (2009), PNAS · Controls on development and diversity of Early Archean stromatolites
Earth history as one day
05:52:0418 h 8 min before midnight
if Earth’s 4.54 billion years were compressed into a single day
See it on the timeline