Федеральное государственное бюджетное учреждение науки
Геологический институт им. Н.Л. Добрецова
Сибирского Отделения Российской академии наук
(ГИН СО РАН)
Мир Бурятия "Гравитация науки: Геологический институт БНЦ СО РАН"
Дайджест мировых новостей:
A cross section of rocks containing the new – but very old – fossil sponges. Photograph: Maloof Lib/Situ Studio
Fossils point to animal life 100m years earlier than thought [2010-08-17] Scientists have found what might be the oldest physical evidence of the existence of animals on Earth.
The fossils of primitive, sponge-like creatures that once lived in ocean reefs off south Australia push back the time at which scientists think the first animal life evolved on Earth by almost 100m years.
The fossilised remains of the 1cm-long sponges in rocks dated at 640-650m years old were found by Adam Maloof, a geologist at Princeton University.
If correct, his finding, published todayin Nature Geoscience, would mean that animal life probably existed before the Marinoan glaciation, an era when the entire planet was covered in ice.
Sponges are simple filter-feeders that extract their food from water as it flows through specialised body channels. Previously, the oldest sponges were about 520m years old, from the Cambrian period.
Before the discovery by Maloof's team, the oldest known fossils of any hard-bodied animals were two sea-dwelling organisms that lived around 550m years ago, called Namacalathus and Cloudina.
But non-fossil evidence has suggested that sponges might be much older. Scientists have analysed DNA in a wide range of creatures to create 'molecular clocks' to work out how long ago they first evolved. According to these, sponges existed millions of years before the Cambrian.
Marc Laflamme of Yale University, said the earliest known sponge fossils were about 555m years old, but that rocks revealed that they should have evolved 90-100m years earlier than that.
'We had chemical and molecular evidence of fossils at this time but we weren't finding any real fossil specimens. What Adam's group was able to find was first evidence of true fossils of sponges at this time.'
That was really important in having three lines of evidence for the early evolution of sponges right before this major snowball Earth event that would have cut off and had some major climate events before the evolution of animals.'
Fossils of ancient animals have traditionally been difficult to study because it is so tough to distinguish the remains of an ancient living organism from the encasing rock using normal techniques. X-rays can only tell the difference between materials of different densities. This makes them useful at imaging bones in the human body but not taking pictures of ancient bones, which are made of calcite, the same substance that makes up the rock in which they are typically embedded.
To get around this problem, Maloof's team joined forces with a US design studio to reconstruct a 3D model digital of the fossil, based on hundreds of photographs.
'We took the fossils home, sliced and diced them up, imaging every 50 microns or so and generating 3D images of these fossils which were otherwise inaccessible to traditional imaging techniques,' he said.
'For many years the great Marinoan ice age has formed a hard floor to the fossil record of animals, ' said Andrew Knoll, an evolutionary biologist at Harvard University. 'Adam and his students are digging deeper and finding that there is much to catch our attention in pre-glacial carbonate rocks … I'm convinced that the structures Adam's group have found are not simply shards of material, formed and deposited by purely physical processes.'
That said, it isn't easy to be sure what they are. Adam's group has carefully spelled out the biological alternatives and built a reasonable case for interpreting the structures as sponge-like animals. At the very least, this should drive paleontologists back to the field to seek similar or better evidence in other rocks of comparable age.' www.topix.com
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Диссертационный совет Д 003.002.01.
К защите принимаются диссертации на соискание ученой степени кандидата и доктора наук по специальностям: 25.00.04 - петрология, вулканология; 25.00.11 - геология, поиски и разведка твердых полезных ископаемых, минерагения
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