Less oxygen killed species
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Oxygen levels were lower for 30 million years
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A PRECIPITOUS drop in atmospheric oxygen levels could be the reason why vertebrates suddenly disappeared around 360 million years ago.
Going by fossil records it is seen that 15 million years later vertebrates reappeared.
Little understanding
There has been little understanding of why the gap (known as Romer's gap) occurred.
Now a team of scientists led by University of Washington palaeontologist Peter Ward has found a similar gap during the same period among non-marine arthropods, largely insects and spiders, and they believe a precipitous drop in the oxygen content of Earth's atmosphere is responsible. "These two groups acted exactly the same way. They proliferated, then they went away, and then they reappeared and multiplied like crazy," said Ward, a UW professor of biology and of Earth and space sciences.
He notes that atmospheric oxygen rose sharply at the end of the Silurian period about 415 million years ago, to reach a level of about 22 per cent of the atmosphere, similar to today's oxygen content.
55 million years later
But 55 million years later, atmospheric oxygen levels sank to 10 per cent to 13 per cent. The level remained low for 30 million years — during which Romer's Gap occurred — then shot up again, and vertebrates and arthropods again began moving from the sea to land, according to a University of Washington press release.
"It matches two waves of colonisation of the land," Ward said. "In the first wave the animals' lungs couldn't have been very good and when the oxygen level dropped it had to be hard for the vertebrates coming out of the water.
I wonder if there is a minimum level of oxygen that has to be reached or nothing could ever have gotten out of the water."
Ward is the lead author of a paper confirming the existence of Romer's Gap, published recently in the Proceedings of the National Academy of Sciences.
In a book authored by him, He argues that dinosaurs became the monsters that ruled the earth for sixty million years and survived the mass extinctions, that led to the disappearance of many other creatures, because of their highly efficient respiratory systems.
Dinosaurs first appeared 230 million years ago during one of the lowest ebbs of atmospheric oxygen for 500 million years earlier but it took some time until oxygen content rose to levels enabling them to grow to their gargantuan sizes.
Their descendents, birds, also have highly efficient respiratory systems. — Our Bureau
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