Pushing back the past

Pushing back the past  australian researchers claim to have discovered evidence that pushes back the date for the first life form on Earth comprehensively. Their findings have shown that life existed on Earth 2.7 billion years ago, 500 million to 1 billion years earlier than previously thought. A recent issue of the journal Science has published these research results.

These life forms are single-celled creatures called eukaryotes. These are the first known cells to have a nuclei and also specialised internal structures for processing energy. Present-day descendants of this group include plants, animals and fungi, as well as single-celled creatures like amoeba.

Based on these findings, the researchers concluded that first life, simple bacteria with no nuclei, appeared around 3.5 billion years ago. The Earth is about 4.6 billion years old. The scientists, led by Jochen J. Brocks, a geoscientist at the University of Sydney, have based their results on fatty molecules produced by living cells found in ancient shale in north-western Australia.

The Australian researchers reported in Science that the abundance of a particular class of chemicals, sterols, are convincing evidence for the presence of eukaryotes around 2.7 billion years ago. Sterols are found in the membranes of eukaryotes.

However, other scientists say that it is not yet ascertained whether the cells that produced the fatty molecules had also developed the other characteristics of eukaryotes. These include structures like choloroplasts, which enable plants to draw energy from the sun through photosynthesis, and mitochondria that enable plant and animal cells to process energy. "All we can say is that one important attribute of eukaryotes was in place 2.7 billion years ago,' Andrew H Knoll, a palaeontologist at the Harvard University Botanical Museum said in an interview.

Nevertheless, Knoll says the discovery highlights two points. First, there was a long interval 1.5 billion years or more, if eukaryotes did arise as long as the new study suggested, between their first appearance and the beginning of their flowering into higher organisms 1.2 billion to 1 billion years ago. Secondly, the findings push back still farther the frontier of investigation of early life. The Brocks findings, Knoll wrote, dramatically lengthen the list of questions we need to ask about evolution.

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