Low-oxygen waters limited habitable space for early animals

Area of Science:

• Geochemistry
• Paleoceanography
• Evolutionary Biology

Background:

• Neoproterozoic oceans were largely anoxic, with progressive oxygenation potentially linked to early animal evolution.
• Previous studies focused on extreme anoxic or oxic conditions, neglecting intermediate redox states.
• The precise role of oxygen in early animal ecosystem development remains poorly understood.

Purpose of the Study:

• To investigate the influence of oxygen levels on early animal ecosystems during the Neoproterozoic Era.
• To reconstruct paleoredox conditions in ancient marine environments.
• To determine the oxygen threshold required for early animal life.

Main Methods:

• Analysis of anomalous cerium enrichments in Nama Group carbonate rocks (Namibia, ~550-541 Ma).
• Utilized iron-based redox proxies to complement geochemical data.
• Examined carbonate rocks across bathymetric transects to infer environmental gradients.

Main Results:

• Anomalous cerium enrichments indicate low-oxygen conditions in a specific zone.
• These low-oxygen zones existed between oxygenated surface waters and anoxic deep waters.
• Early skeletal animals were absent from these oxygen-impoverished areas.

Conclusions:

• Low-oxygen conditions (<10 μM) were a significant environmental filter for early animal ecosystems.
• Oxygen availability was a critical factor for the proliferation and development of early animal life.
• The study highlights the importance of intermediate redox levels in understanding marine ecosystem evolution.