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Finding an answer to Darwin's Dilemma
December 11, 2006Oxygen may be the clue to first appearance of large animals, says Queen's prof
The sudden appearance of large animal fossils more than 500 million years ago - a problem that perplexed even Charles Darwin and is commonly known as "Darwin's Dilemma" - may be due to a huge increase of oxygen in the world's oceans, says Queen's paleontologist Guy Narbonne, an expert in the early evolution of animals and their ecosystems.
In 2002, Dr. Narbonne and his research team found the world's oldest complex life forms between layers of sandstone on the southeastern coast of Newfoundland. This pushed back the age of Earth's earliest known complex life to more than 575 million years ago, soon after the melting of the massive "snowball" glaciers. New findings reported today shed light on why, after three billion years of mostly single-celled evolution, these large animals suddenly appeared in the fossil record.
In a paper published on-line in Science Express, Dr. Narbonne's team argues that a huge increase in oxygen following the Gaskiers Glaciation 580 million years ago corresponds with the first appearance of large animal fossils on the Avalon Peninsula in Newfoundland.
Now for the first time, geochemical studies have determined the oxygen levels in the world's oceans at the time these sediments accumulated in Avalon. "Our studies show that the oldest sediments on the Avalon Peninsula, which completely lack animal fossils, were deposited during a time when there was little or no free oxygen in the world's oceans," says Dr. Narbonne. "Immediately after this ice age there is evidence for a huge increase in atmospheric oxygento at least 15 per cent of modern levels, and these sediments also contain evidence of the oldest
large animal fossils."
Also on the research team are Don Canfield (University of Southern Denmark) and Simon Poulton (Newcastle University, U.K.). Geochemical studies by Drs. Canfield and Poulton included measurements of iron speciation and sulphur isotopes to determine the oxygen levels in the world's oceans at the time these sediments accumulated in Avalon.
The close connection between the first appearance of oxygenated conditions in the world's oceans and the first appearance of large animal fossils confirms the importance of oxygen as a trigger for the early evolution of animals, the researchers say. They hypothesize that melting glaciers increased the amount of nutrients in the ocean and led to a proliferation of single-celled organisms that liberated oxygen through photosynthesis. This began an evolutionary radiation that led to complex communities of filter-feeding animals, then mobile bilateral animals, and ultimately to the Cambrian "explosion" of skeletal animals 542 million years ago.
Queen's University
In a paper published on-line in Science Express, Dr. Narbonne's team argues that a huge increase in oxygen following the Gaskiers Glaciation 580 million years ago corresponds with the first appearance of large animal fossils on the Avalon Peninsula in Newfoundland.
Now for the first time, geochemical studies have determined the oxygen levels in the world's oceans at the time these sediments accumulated in Avalon. "Our studies show that the oldest sediments on the Avalon Peninsula, which completely lack animal fossils, were deposited during a time when there was little or no free oxygen in the world's oceans," says Dr. Narbonne. "Immediately after this ice age there is evidence for a huge increase in atmospheric oxygento at least 15 per cent of modern levels, and these sediments also contain evidence of the oldest
large animal fossils."
Also on the research team are Don Canfield (University of Southern Denmark) and Simon Poulton (Newcastle University, U.K.). Geochemical studies by Drs. Canfield and Poulton included measurements of iron speciation and sulphur isotopes to determine the oxygen levels in the world's oceans at the time these sediments accumulated in Avalon.
The close connection between the first appearance of oxygenated conditions in the world's oceans and the first appearance of large animal fossils confirms the importance of oxygen as a trigger for the early evolution of animals, the researchers say. They hypothesize that melting glaciers increased the amount of nutrients in the ocean and led to a proliferation of single-celled organisms that liberated oxygen through photosynthesis. This began an evolutionary radiation that led to complex communities of filter-feeding animals, then mobile bilateral animals, and ultimately to the Cambrian "explosion" of skeletal animals 542 million years ago.
Queen's University
Darwin Current Events and Darwin News RSSFunny, you don't look related
When Charles Darwin visited the Falkland Islands during the voyage of the Beagle in 1835, he saw a wolf-like species, wrote about it in his diaries and correctly commented that it was being hunted in such large numbers that it would soon become extinct.
Darwin meets Facebook
Natural history plans to chart life on earth, yet the discipline risks being buried under a landslide of painstakingly collected data that isn't always used.
AIBS publishes Darwin articles open access
To celebrate the 150th anniversary this month of the publication of On the Origin of Species, the American Institute of Biological Sciences (AIBS) is publishing open access two peer-reviewed articles about Charles Darwin and his historic insights into evolution.
Ants are friendly to some trees, but not others
Tree-dwelling ants generally live in harmony with their arboreal hosts. But new research suggests that when they run out of space in their trees of choice, the ants can get destructive to neighboring trees.
Inconspicuous leaf beetles reveal environment's role in formation of new species
Unnoticed by the nearby residents of St. Johnsbury, Vermont, tiny leaf beetles that flit among the maple and willow trees in the area have just provided some of the clearest evidence yet that environmental factors play a major role in the formation of new species.
Charles Darwin really did have advanced ideas about the origin of life
When Charles Darwin published The Origin of Species 150 years ago, he deliberately avoided the subject of the origin of life.
A solution to Darwin's 'mystery of the mysteries' emerges from the dark matter of the genome
Biological species are often defined on the basis of reproductive isolation. Ever since Darwin pointed out his difficulty in explaining why crosses between two species often yield sterile or inviable progeny (for instance, mules emerging from a cross between a horse and a donkey), biologists have struggled with this question.
2-million-year-old evidence shows tool-making hominins inhabited grassland environments
In an article published in the open-access, peer-reviewed journal PLoS ONE on October 21, 2009, Dr Thomas Plummer of Queens College at the City University of New York, Dr Richard Potts of the Smithsonian Institution National Museum of Natural History and colleagues report the oldest archeological evidence of early human activities in a grassland environment, dating to 2 million years ago.
New type of flying reptile discovered
An international group of researchers from the University of Leicester (UK), and the Geological Institute, Beijing (China) have identified a new type of flying reptile - providing the first clear evidence of an unusual and controversial type of evolution.
Early hominid first walked on two legs in the woods
Among the many surprises associated with the discovery of the oldest known, nearly complete skeleton of a hominid is the finding that this species took its first steps toward bipedalism not on the open, grassy savanna, as generations of scientists - going back to Charles Darwin - hypothesized, but in a wooded landscape.
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