and revealing the origin and fate of the universe.
About the time that the continents began to grow and began, Earth produced its first known glaciers, between 3.0 and 2.9 bya, although the full extent is unknown. It might have been an ice age or merely some mountain glaciation. The , and numerous competing hypotheses try to explain what produced them. Because the evidence is relatively thin, there is also controversy about the extent of Earth's ice ages. About 2.5 bya, the Sun was probably a little smaller and only about as bright as it is today, and Earth would have been a block of ice if not for the atmosphere’s carbon dioxide and methane that absorbed electromagnetic radiation, particularly in the . But life may well have been involved, particularly oxygenic photosynthesis, and it was almost certainly involved in Earth's first great ice age, which may have been a episode, and some pertinent dynamics follow.
In photosynthesis, what is the fate of the oxygen ..
As oxygenic photosynthesis spread through the oceans, everything that could be oxidized by oxygen was, during what is called the (“GOE”), although there may have been multiple dramatic events. The event began as long as three bya and is . The ancient carbon cycle included volcanoes spewing a number of gases into the atmosphere, including hydrogen sulfide, sulfur dioxide, and hydrogen, but carbon dioxide was particularly important. When the continents began forming, carbon dioxide was removed from the atmosphere via water capturing it, , the carbon became combined into calcium carbonate, and plate tectonics subducted the calcium carbonate in the ocean sediments into the crust, which was again released as carbon dioxide in volcanoes.
It can help to think of mitochondria as “distributed” energy generation centers in eukaryotes, versus the “perimeter” energy generation in prokaryotes. The new mode of energy production presented various challenges, but it allowed life to become large and complex. Size is important, at the cellular level as well as the organism level. Below is a diagram of a typical plant cell. (Source: Wikimedia Commons)
Cellular Respiration PowerPoint with Teacher Lecture Notes and ..
About 1 bya, began to decline and microbial photosynthesizers , probably due to predation pressure from , which are eukaryotes. Eating stromatolites may reflect the of , although grazing is really just a form of predation. The difference between grazing and predation is the prey. If the prey is an (it fixes its own carbon, by using energy from either or ), it is called grazing, and if the prey got its carbon from eating autotrophs (such creatures are called ), then it is called . There are other categories of life-form consumption, such as and (eating dead organisms), and there are many instances of . For complex life, the symbiosis between the and its cellular host was the most important one ever.
the reactants and products of photosynthesis and respiration, ..
The dates are controversial, but it appears that after hundreds of millions of years of using various molecules as electron donors for photosynthesis, began to split water to get the donor electron, and oxygen was the waste byproduct. Cyanobacterial colonies are dated to as early as 2.8 bya, and it is speculated that may have appeared as early as 3.5 bya and then spread throughout the oceans. Those cyanobacterial colonies formed the first fossils in the geologic record, called . At Shark Bay in Australia and some other places the water is too saline to support animals that can eat cyanobacteria, and give us a glimpse into early life on Earth.
Future of an expanding universe - Wikipedia
Just as were “invented,” somewhere between 1.6 bya and 600 mya a eukaryote ate a cyanobacterium and both survived, and that cyanobacterium became the ancestor of all chloroplasts, which is the photosynthetic organelle in all plants. As with similar previous events, it appears that it , and all plants are descended from that unique event. The invention of the chloroplast , which were the first plants. The first algae fossils are from about 1.2 bya. Most algae species are not called plants, as they are not descended from that instance when a eukaryote ate a cyanobacterium. The non-plant algae, such as , also have chloroplasts, from various “envelopment” events when algae chloroplasts were eaten and the grazers and chloroplasts survived. Below is the general outline of the tree of life today, in which bacteria and archaea combined to make eukaryotic cells, and in which the bacterium enveloped into a protist to make plants, and all complex life developed from protists. (Source: Wikimedia Commons)
Human Knowledge: Foundations and Limits
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.