Tracking a Trail
by BradfordHow old is the oldest evidence for complex life forms? The Science News article Oldest evidence for complex life in doubt discusses that matter. I would hasten to point out that one of the hallmarks of even unicellular organism is intrinsic complexity. It's not as if simple life forms are available to serve as contrasts. Nevertheless there have been attempts to ascertain when it was that ancient organisms related to cyanobacteria first appeared on earth.
In 1999 researchers published a finding indicating that the origin of cyanobacteria was at least 550 million years closer to the time origin of the earth itself. It is believed that single celled organisms were the first life forms followed by cyanobacteria which had photosynthesis capabilities. That in turn is important in assessing when it was that the earth acquired a significant amount of atmospheric oxygen. The article states:
Results of the first analyses of the Australian rocks (SN: 8/28/99, p. 141) were controversial, says Birger Rasmussen, a geochemist at Curtin University of Technology’s campus in Bentley, Australia. For one thing, the shale — which had been laid down as sediments about 2.7 billion years ago — contained tiny particles of pyrobitumen, coal-like remnants of oil droplets that had solidified as the sediment layers cooked. Pyrobitumen is a sign that the sediments and any organic material they contained experienced temperatures from 200° Celsius to 300°C for an extended time. The rocks also contained significant amounts of kerogen.
Yet the samples also held small quantities of hopanes, a class of organic chemicals produced by cyanobacteria and some other bacteria, as well as steranes, which are produced only by eukaryotes. That the rocks hosted these biomarkers, which should have been destroyed by the heat and pressure required to generate the pyrobitumen, “presented a bit of a conundrum,” Rasmussen says.
Newer more precise measuring instruments were used to find the proportion of the carbon-13 isotope found in kerogen and other hydrocarbons. Between 1 and 3 parts per thousand less than the proportion found in the original derivative organic matter is expected. Yet the proportions of carbon-13 isotopes of the kerogen and pyrobitumen in the Australian rocks examined was between 10 and 20 parts per thousand less than those found in the hopanes and steranes. Based on this researchers found a strong indicator of biomarker migration into rocks thereby indicating that biomarkers were likely to be unrelated to kerogen and the pyrobitumen.
Some though believe the biomarkers could still be legitimate indicators of early complex life. The quest to fix a time to the appearance of complex life forms continues.
November 8th, 2008 at 11:04 am
This quote provides perspective and indicates the importance of understanding what might otherwise appear to be a dry subject matter:
Not only were microbes the first living things on Earth, they were critical to the Earth's transformation. The rise of photosynthetic bacteria called cyanobacteria was a crucial step because these bacteria ingested carbon dioxide and released oxygen.
They multiplied until eventually they were producing more oxygen than the planet's natural processes consumed, and oxygen began to build up in the atmosphere.
"Most of the life on the planet is microbial," Knoll said. "You can certainly run a world without dinosaurs and humans, but you can't do it without microbes."
Comment by Bradford — November 8, 2008 @ 11:04 am
November 8th, 2008 at 3:47 pm
Hi Bradford,
In a lot of ways discussions of origin of life are rigged by only focusing on complex life. As you know, I have had a continuing interest in nanobes (or nanobacteria). I suggest that they may be of cosmic origin (found on asteroid ALH 84001), they contain DNA and form "colonies" that grow.
It is getting more and more of an unsupportable argument that life had to start on Earth because conditions would be too harsh anywhere else.
Here is a link to a relevent paper…
"Microorganisms known as thermophiles and hyperthermophiles are present at temperatures above boiling point in oceanic thermal vents. Entire ecologies of microorganisms are present in the frozen wastes of the Antarctic ices. A formidable total mass of microbes exists in the depths of Earth’s crust, some 8 kilometres below the surface, greater than the biomass at the surface11. A species of phototropic sulfur bacterium has been recently recovered from the Black Sea that can perform photosynthesis at exceedingly low light levels, approaching near total darkness12. There are bacteria (e.g., Deinococcus radiodurans) that thrive in the cores of nuclear reactors."
Here is a link to a paper on nanobacteria…
"Recent evidence suggests a role for nanobacteria in a growing number of human diseases, including renal stone formation, cardiovascular diseases, and cancer. This large body of research studies promotes the view that nanobacteria are not only alive but that they are associated with disease pathogenesis."
Bradford, even the paper you sited in the opening post doesn't refute evidence of early life on Earth, it only questions one particular piece of evidence (found in shale formations) for particular COMPLEX life forms.
In short, the origin of life on Earth may have had a big assist from the origin of life in space.
Comment by Thought Provoker — November 8, 2008 @ 3:47 pm
November 9th, 2008 at 6:24 am
Of course. Then again various particular life forms are complex. Deinococcus radiodurans are extremely interesting organisms and merit more attention within the context of a separate blog entry.
Comment by Bradford — November 9, 2008 @ 6:24 am
November 9th, 2008 at 11:34 am
[...] Bradford at Telic [...]
Pingback by When Did Life Appear? | The Design Matrix — November 9, 2008 @ 11:34 am