Question

Explain the proposed relationship between evolution of eukaryotes and the evolution of ocean chemistry.

Answer 1

In proterozoic eon that is 2500 to 543mya Earth's oceans were sulfidic at depths and oxic on the surface. These conditions did not favour much of the biologically important trace metals leading to their scarcity in marine environment. This ultimately restricts the nitrogen cycle, decreased primary productivity and limited distribution of eukaryotic algae.

Evolutionary patterns in fossils of "proterozoic eukaryotes"are explained by presence of trace elements in very less amounts in the sulfidic seas. This suggests that there is a "bioinorganic bridge" between evolution of eukaryotes and ocean chemistry.

Molybdenum and copper scarcity in sulfidic oceans might have increased the problem in eukaryotes of assimilating nitrogen. In cyanobacteria, depletion of ammonia result in formation of transcriptional regulators. hence, under limited nutrients eukaryotic algae compete effectively when N is available allowing them to store fixed N. In today's oceans large algae growth is favoured by high NO3 levels.