LIFE × EVOLUTION

Bangiomorpha: the Oldest Red Alga

~1.05 billion years ago

Proterozoic · Mesoproterozoic · Stenian

Bangiomorpha, a red alga fossilised in Arctic Canada about 1.05 billion years ago, is the oldest organism that can be assigned to a group still living.

Bangiomorpha is a red alga fossilised in Arctic Canada. It presents three features not known together in any older organism. First, its cells are differentiated: a holdfast, a base that anchors the alga, bears filaments that rise from it. The cells have therefore specialised and can no longer live independently. Second, it carries out photosynthesis within a complex cell, which establishes that the chloroplast, the compartment of the cell where photosynthesis takes place, had already been acquired. Third, it produces spores, its reproductive cells, of two distinct kinds, which is to say that it reproduces sexually.

Why it matters

Cells that adhere to one another form a colony. Cells that specialise and depend on one another form an organism, and Bangiomorpha is the oldest organism that can be assigned to a living group. Its position in the tree of red algae is known, so its age calibrates the molecular clock for every branch below it. The molecular clock is the method that dates the branching of lineages from the differences accumulated between their genes. When Gibson and colleagues (2017) redated the fossil, the calibration moved by 150 million years.

Dating & uncertainty

Bangiomorpha is the oldest multicellular eukaryote, an organism made of complex cells, that can be assigned to a modern group. It is not the oldest multicellular organism. Colonial forms such as Horodyskia are reported from rocks of the Tonian, a geological period, and simple multicellular fossils reach back to about 1.6 billion years ago. Its own age was revised from the long-accepted 1.2 billion years to 1.047 billion years. The newer, younger age comes from rhenium-osmium dating of the enclosing beds, a method that measures the radioactive decay of rhenium into osmium.

Earth history as one day

18:26:575 h 33 min before midnight

if Earth’s 4.54 billion years were compressed into a single day