BBC - April 2004
Scientists have discovered evidence for the earliest known wildfire in Earth's history, the journal Geology reports.
It comes in the form of small plant fossils preserved as charcoal, which were unearthed by researchers near the town of Ludlow on the Welsh borders.
The plant remains date to the Silurian Period, about 443 to 417 million years ago, say a Cardiff University team.
Previously, charcoal was known only from the later Devonian Period, which saw an explosion in plant diversity.
But in the Silurian, plants were generally quite small, which would have restricted the fuel source for wildfires.
"The plants were only a few centimetres in height.
"It's amazing that there should be an accumulation of vegetation, either as litter or as living vegetation drying out - to provide fuel for a fire," co-author Professor Dianne Edwards of Cardiff University told BBC News Online.
"And even more amazing that a lightning strike set it off."
Feeling the heat
The team used a technique known as reflected-light microscopy on a collection of well-preserved plants recovered from a dig at Ludford Lane.
The fossils are preserved in three-dimensions, rather than being compressed. This is unique amongst Silurian plant remains.
Charcoal has a high optical reflectance due to chemical changes that occur when organic material burns. The results confirmed that this was the case for the Silurian plants.
The researchers also found other evidence that the fossils were charred such as shrinkage of the layer of cells, or epidermis, which covers the surface of the plant.
In Geology, the University of Cardiff team proposes that the exceptional three-dimensional preservation of the plants is due to their charring in a wildfire.
However, comparisons with the reflectance values of experimentally charred plants show most of the Ludford Lane specimens were only partially turned to charcoal.
Millipede traces
This indicates that they were burnt by either a short-lived low-temperature fire or a smouldering fire that was only intense enough to partially char them.
This agrees well with proposed compositions for the Silurian atmosphere.
Oxygen levels are supposed to have been lower in Silurian times; about 18% compared with present-day levels of roughly 21%.
Lower levels of oxygen in the atmosphere, combined with a restricted fuel source, may have produced less intense wildfires and therefore less reflective charcoal.
Professor Edwards said that the fire might have been similar to a modern heathland fire.
"The climate of the time would have had some extremely dry seasons as well as wet seasons. There would have been aridity and presumably plants would have dried out," she explained.
"Or there could have been accumulations of plants that had been in floods and that could have formed a fuel."
The researchers also found a charred coprolite - fossilised faeces - amongst the Ludford Lane specimens which probably came from a millipede.
BBC - March 2004
Human-like species living in Africa up to 1.5 million years ago may have known how to control fire, scientists say.
US and South African experts analysed burnt bones from Swartkrans, just north of Johannesburg, using the technique of electron spin resonance.
It showed the bones had been heated to high temperatures usually only achieved in hearths, possibly making it the first evidence of fire use by humans.
The results will be presented at the 2004 Paleoanthropology Society Annual Meeting in Montreal, Canada, in March.
The research is a collaboration between South African researchers Dr Bob Brain and Dr Francis Thackeray of the Transvaal Museum in Pretoria, and researchers at Williams College in Williamstown, US.
"These bones could have been burnt in a forest fire or brush fire but that's generally a low temperature flame. These had been heated to a very high temperature," Dr Anne Skinner, of Williams College, told BBC News Online.
Electron Spin Resonance (ESR) looks at free radicals, fragments of molecules produced by a variety of processes, such as radiation damage or fire.
Studying the light signature, or spectra, produced by these free radicals can give scientists information on the nature of the damage.
As organic material, such as bone and collagen, is broken down by heating, the particles get smaller and smaller until only the carbon is left.
Given the brush
"What I was doing was taking these bones and seeing whether in fact I could see electron spin resonance spectra getting progressively smaller and ending up with carbon," said Dr Skinner.
Forest or brush fires usually only reach temperatures of around 300 degrees Celsius. But hearths or campfires can reach temperatures of 600 degrees Celsius or more.
The burnt bones were first described by Dr Bob Brain and Dr Andrew Sillen of the University of Cape Town in 1988. Dr Brain found that the burnt bones from Swartkrans could be sorted into types that had been burnt at low and high temperatures.
He also found that if modern bones were heated at low temperatures for long periods of time they began to look like bones that had been heated to high temperatures in a camp fire.
However, the electron spin resonance data would seem to confirm original suggestions about the bones.
This is because the degree of carbonisation of organic material as measured with electron spin resonance is dependent only upon the amount of carbon and not on the time material has been heated for.
It is not known which hominid species made the fires at Swartkrans. There seem to have been two hominid species present at Swartkrans around two million years ago.
These were Australopithecus (or Paranthropus) robustus and an early species of Homo, possibly Homo erectus.
The next oldest evidence for controlled use of fire may come from Zhoukoudian in China, dating to between 400,000 and 250,000 years ago.
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