Geologists at Northwestern University are studying periods of low oxygen that occurred in oceans as far back as 252 million years ago, according to Medill Reports Chicago. They’re using rock cores extracted thousands of feet below the ocean floor to do it.
The mesozoic-era cores, rich in carbon and containing large amounts of organic matter, indicate oceans at the time were largely anoxic. Warming during the period likely caused higher rates of weathering on land that released nutrients into oceans that fed algal blooms. Scientists say the blooms eventually died due to low oxygen levels and sank to the bottom.
The cores provide an excellent reference point because they come from a climate similar to today’s. Though warming in the mesozoic era is believed to have come from CO2 emissions by volcanoes, today’s warming is largely believed to come from the burning of fossil fuels.