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Lecture 10

Lecture 10

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Biological Sciences
Herbert Kronzucker

BGYC61H3 Lecture 10 November 17 2008 The important recognition that some 99% of all the species that have existed on the planet over history have vanished. The number of species today estimated to be alive is 32 to 100 and some put it about 100 million and nobody argues that there is more than that. E.O. Wilson is in the biodiversity field and has done work on insect biodiversity in particular but he exaggerates a little. Never before in history have there been that many species alive and this is not surprising. The ongoing forces to diversify would have to bring about larger and larger diversity of species. It is not a continual process. When life first took root on the planet went from Ediacaran from multi-cellular life divergence followed by a bigger explosion in the Cambrian (Darwin wrote about this). Bacteria organisms have been around much longer from Achaean period which is under debate (roughly 3.5 billion years old). There are other fossils now from S. Africa, Greenland, and Canada but we are pretty sure that 2.5 billion years ago there was life. From that stretch of time onwards the diversity of life has increased. It of course has not been continuous there have been bursts of species disappearances. There have been 5 mass extinction events that are well documented in fossil beds. They all happened after the blue line (signifies about the Cambrian explosion (600 million years ago) and that is the beginning of multi-cellular life. The Burgess Shales in the Rocky Mountains come from this time (505 to 530 million years old). The Ediacaran life forms were in the oceans and were animals and they didnt predate on each other. They absorbed nutrients from the environment. Before Cambrian life there was at least 1 other major life extinction that brought these life forms to their knees. It is now the tooth and claw. Prior to the Ediacaran there were extinctions during that time as well but they are poorly documented, microbes are difficult to pin down in beds. They decompose and maybe leave a footprint behind. These disappearances prior to the Ediacaran did experience several massive climate change episodes throughout the planet that much have brought the organisms to their knees. A time period that was fairly lengthy. It was known as Snowball Earth. This concept is fairly recent and came into our consciousness when you were in high school. It was almost as long as the reign of the dinosaurs and many believe most of the planet was covered in ice. The last major ice age ended 10,000 years ago and peaked at around 18,000 and 15,000 years ago. That was the last major ice age in these parts of the world and Toronto was covered by 1.6 km of ice and near Hudsons Bay it could have been about 3 km deep. This was when humans were already in this part of the world. Snowball Earth was 790 to 630 million years ago. Most experts believe that the majority if not all was covered just like Toronto at the peak of the last ice age. An ice age as long as 160 million years or so that life forms that existed in the tropics for example would have been brought to their knees and also unicellular life forms. All adapted to reasonable climate conditions. There is no question that a majority of life has been brought to its knees and certainly during Snowball Earth. Life after earth melted in parts of the world BGYC61H3F.November.17.2008 Lecture 10 1
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