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 Post subject: Photosynthesis Synthesis
PostPosted: Wed Jul 31, 2013 9:19 pm 
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We all think of leaves as beautiful, flat, green parts which symbolize the health and vitality of a plant. They represent life and photosynthesis to many of us. They represent autumn to many more of us. In the end, most people don’t realize the changes that have occurred to create such structures, and how a leaf may not be a foregone conclusion.

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As in previous posts, I have mentioned that the earliest true plants on the Earth were flat and small organisms, hugging the ground but still able to intercept light to conduct photosynthesis. In the end, it’s all about light and photosynthesis for life on Earth. In fact, maybe we should take a “step back” and look at the advent of photosynthesis on Earth, because this is where explorers of distant worlds will want to focus.

As most (educated) people know the Earth is very old: somewhere around 4.7 billion years old. In the beginning, known as the Hadean Eon (4.0-4.7 bya), Earth was fairly inhospitable. A world of hot molten Earth and toxic gases, but what is fascinating, and encouraging to planet explorers, is that life appears to appear in a relatively short period time after this.

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Above: the Hadean Eon (J. Boyer)

Many researchers infer that life probably evolved somewhere between 3.6 and 4.0 billion years ago during the Eoarchean Era. Even though we don’t have many reliable rocks to decipher this time period, we have some of the earliest rocks which come the southwest of Greenland dating to 3.8 bya. We can infer from chemical analysis of rocks that the atmosphere had high concentrations of methane, ammonia, and carbon dioxide. In addition, we know that the sun wasn’t as bright and warm as present day, but the temperature of the Earth was mild to warm since the core produced three times as much heat as today. Under an orange sky and dim sunset, this is where bacteria evolved, probably using methane as an energy source.

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Above: A stromatolite, a cyanobacteria formed structure, from the Paleoarchean (wiki commons)

If we jump to the Paleoarchean Era (3.2–3.6 billion years ago), we start to find indirect evidence of bacteria in fossils from Western Australia. There is evidence that purple bacteria were conducting non-oxygen generating photosynthesis. Other bacteria, known as cyanobacteria, were probably evolving, conducting photosynthesis that we know and love: carbon dioxide come in, oxygen goes out. This latter group was going to change the world into the oxygen-rich atmosphere that we have today.

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Above: A possible early algae, Grypania (wiki commons)

If we time-warp an dazzling three billion years into the future, we start to see evidence of the first plants. This means that bacteria dominated the Earth for a very long time. Even algae don’t appear until about a billion years ago. We may get lucky someday to find a planet that has created plants similar to our earliest liverworts, but space travelers should probably keep their eyes open for bacteria.


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PostPosted: Fri Aug 02, 2013 10:23 am 
Broken Crown Founder
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Joined: Sun Jun 10, 2012 4:48 pm
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I love the stromatolite from the Paleoarchean!

Knowing cyanobacteria flurished in a colder, dimmer, methane based early Earth is always exciting to think about when looking at Titan as a potential terraform candidate. It means we may not even be the first "life" on that planet when we get there.

Very cool.

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