Essay - Introduction The oceans of the earth are a massive part ..
WEEKLY ESSAY WRITING CHALLENGE - INSIGHTS
When the total continental land mass was small or combined into a supercontinent, there was no land to divert that diffusion of warm water toward the poles, which results in currents. During those times, the global ocean became one big, calm lake, with no currents of significance. Those oceans are called today, and they would have been anoxic; the oxygenated surface waters would not have been drawn by currents to the ocean floor, and the oceans were certainly anoxic before the GOE. The interplay of those can be incredibly complex and lead to the multitude of hypotheses posited to explain those ancient events, but a leading hypothesis today is that a combination of factors, including supercontinents, variations in volcanic output, Canfield Oceans, and ice ages prevented life from gaining ecosystem dominance until the waning of the second Snowball Earth event, which was the greatest series of glaciations that Earth has yet experienced. It is known today as the , which ended about 635 mya. The study of the Cryogenian Period, which is the subject of , resulted in the term “.”
WEEKLY ESSAY CHALLENGES – 2015
During that “,” , , and the rise of grazing and predation had eonic significance. While many critical events in life’s history were unique, one that is not is multicellularity, , and some prokaryotes have multicellular structures, some even with specialized organisms forming colonies. There are , but the primary advantage was size, which would become important in the coming eon of complex life. The rise of complex life might have happened faster than the billion years or so after the basic foundation was set (the complex cell, oxygenic photosynthesis), but geophysical and geochemical processes had their impacts. Perhaps most importantly, the oceans probably did not get oxygenated until just before complex life appeared, as they were sulfidic from 1.8 bya to 700 mya. Atmospheric oxygen is currently thought to have remained at only a few percent at most until about 850 mya, although there are recent arguments that it remained low until only about 420 mya, when large animals began to appear and animals began to colonize land. Just as the atmospheric oxygen content began to rise, then came the biggest ice age in Earth’s history, which probably played a major role in the rise of complex life.