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Earth’s Oldest Fossils Could Provide Clues to Life on Other Planets 地球上最古老的化石可能提供外星生命的线索

August 23, 2011

Origin from VOA 原文来自VOA


翻译:George Lam

Researchers from England and Australia recently found some microfossils in a remote part of Western Australia.


Before you click away and say, “Big deal another fossil find,” hang with me for a bit.


The microscopic fossils, according to the researchers, are 3.4 billion years old, making them Earth’s oldest fossils.


The fossils resulted from life forms which lived on our planet before Earth even had oxygen.


Wow!  Kind of hard to visualize Earth without its life-giving oxygen, isn’t it?


OK, lets step back to the time when Earth first formed.


Most scientists generally agree that our planet is between 4.5 and 4.6 billion years old.


Soon after being formed, Earth was a huge molten hunk of rock with no atmosphere and, of course, none of the characteristics that make our planet special.


At this time, Earth’s core was also still forming. There was no solid inner core or  liquid outer core, like there is today, so the world wasn’t able to retain gasses very well.


Scientists describe our first atmosphere as being composed of hydrogen and helium, two elements which were very common when Earth and the rest of the solar system were formed.

Because of the heat and unformed core, these gasses soon escaped from Earth into space.


Earth continued its cooling process and, as the core began to stabilize, the earth’s magnetic fields were formed.


A more stable core and a cooler planet meant that more of the gasses produced by our evolving world could be retained closer to its surface.


As volcanic activity began and continued to increase throughout the planet, a lot of different gases formed as a result.


These included carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (S2), chlorine (CL2), nitrogen (N2), deuterium, also called heavy hydrogen (H2), ammonia (NH3) and methane (CH4).


The volcanoes also produced a lot of steam (water/H2O), but no free existing oxygen (O2).


Oxygen was later produced and introduced into our atmosphere through two processes; photochemical dissociation, caused by the breakup of water molecules by the sun’s ultraviolet light, and photosynthesis, the process that uses carbon dioxide and water (H2O) to form organic compounds while also releasing oxygen (O2).


Early forms of life that developed and lived during this “pre-oxygen time”, some 3.4 billion years ago, were sulfur-based cells and bacteria which lived off metabolized compounds which had sulfur, rather than oxygen, for energy and growth.


The researchers, from the University of Western Australia and England’s  Oxford University,  say their discovery of these microfossils provides convincing evidence that these unique early life forms did exist.


Oxford Professor Martin Brasier, one of the team’s leaders, says the life forms of the fossils still exist and are common today.

团队领导之一、牛津大学教授Martin Brasier说,这些化石的生命形式今天依然普遍存在。

The sulfur-based bacteria can be found in smelly ditches, soil, hot springs, hydrothermal vents – anywhere there’s little free oxygen and they can live off organic matter.


Professor Brasier says their discovery also has implications in the search for life on other planets, giving scientists an indication of what evidence for such life might look like.


A report on this finding can be found in the journal Nature Geoscience.

在Nature Geoscience杂志上有一篇关于这个发现的报道。


From → English

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