24-02-2017 2/2 Fossil Evidence Of Change Study Guide Answers.
The Fossil Records and Theories of Evolution.
Scientists often measure extinction rates at the and levels of the taxonomy; families and genera are far harder to kill off than species. Some genera/families beat the odds and survived for hundreds of millions of years. They are called , and usually all of their close relatives went extinct long ago. The ubiquitous and lowly is a living fossil that first appeared nearly 400 mya. There have been recent calls to retire the "living fossil" designation, as the survivors of their lines have evolved somewhat over the years. However, it was not all that much, as they were very recognizable decedents of nearly identical-looking ancestors, and if those "living fossils" were graphically represented on the tree of life, they might instead be called the last leaves on their branch. Perhaps "sole survivor" conveys the meaning better. However scientists want to term it, the fact is that those "living fossils" have an ancient lineage, have not appreciably changed in millions of years, and the large "family" that they descended from all went extinct; their branch is bare except for them. The survivors evolved since their close relatives died out, but there is nothing close to them on their branch of the tree of life.
Fossil evidence has been used to support evolution.
There is also evidence that life itself can contribute to mass extinctions. When the eventually , organisms that could not survive or thrive around oxygen (called ) . When anoxic conditions appeared, particularly when existed, the anaerobes could abound once again, and when thrived, usually arising from ocean sediments, they . Since the ocean floor had already become anoxic, the seafloor was already a dead zone, so little harm was done there. The hydrogen sulfide became lethal when it rose in the and killed off surface life and then wafted into the air and near shore. But the greatest harm to life may have been inflicted when hydrogen sulfide eventually , which could have been the final blow to an already stressed ecosphere. That may seem a fanciful scenario, but there is evidence for it. There is fossil evidence of during the Permian extinction, as well as photosynthesizing anaerobic bacteria ( and ), which could have only thrived in sulfide-rich anoxic surface waters. Peter Ward made this key evidence for his , and he has implicated hydrogen sulfide events in most major mass extinctions. An important aspect of Ward’s Medea hypothesis work is that about 1,000 PPM of carbon dioxide in the atmosphere, which might be reached in this century if we keep burning fossil fuels, may artificially induce Canfield Oceans and result in . Those are not wild-eyed doomsday speculations, but logical outcomes of current trends and , proposed by leading scientists. Hundreds of already exist on Earth, which are primarily manmade. Even if those events are “only” 10% likely to happen in the next century, that we are flirting with them at all should make us shudder, for a few reasons, one of which is the awesome damage that it would inflict on the biosphere, including humanity, and another is that it is entirely preventable with the use of technologies .