You will notice that a plant cell has a cell wall, whereas animal cells do not have a cell wall.
A mass extinction event occurs when a species disappears far more quickly than it is replaced. This is typically understood as the loss of around 75% of all species over a "short" period of geological time, or fewer than 2.8 million years.
An enormous number of species were wiped out by a harsh, worldwide, swift, and selective event is mass extinction. According to marine fossils, at least 75% of all species are thought to have become extinct. The most recent mass extinction is the Cretaceous-Paleogene extinction event, which is also the only one that can be proven to have been caused by a significant asteroid impact. All non-avian dinosaur species, making up about 76 percent of all species on the earth, perished during mass extinction. The Chicxulub asteroid impact in what is now Mexico, which occurred 66 million years ago, caused an ecosystem collapse that resulted in the extinction of the dinosaurs and >75% of all land and sea species as well as the macroevolution of mammals.
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<span>Ozone is simply a molecule consisting of 3 oxygen atoms, which reacts strongly with other molecules. Ozone is created in the stratosphere when high energy uv radiation causes on O2 molecule to split. The free oxygen atoms collide and react with other O2 molecules to form O3.</span>
Production is highest where the solar uv is the greatest eg near the tropics, but once created, the ozone is then circulated towards the poles by the atmosphere. The amount of ozone in the stratosphere can vary with location, season and even day to day climatic conditions.
<span>The process of ozone creation is what makes the O3 in the atmosphere very effective at shielding the Earth from harmful uv radiation, which can cause many biological problems, such as skin cancer. However, due to its high reactivity, the uv found in the tropospher at ground level can aslo be dangerous as a toxic pollutant which is harmful to plants and lung tissue, and is a major cause of smog.</span>
