Claire Smerdon's Science Blog

         One major event is the Earth gaining oxygen. Originally, the Earth had 0% oxygen, before gradually accumulating it. This is major because we would not be here today without it. Another significant event was the Permian-Triassic mass extinction, which wiped out more than 90% of species. This greatly shapes the species we find on Earth today. Another large event was the Triassic-Jurassic extinction. This wiped out all the dinosaurs. This is significant because it led room for humans.           Earth has been around for a very long time, and what surprised me most was how long it had no life. In such a short time, we have dramatically changed our Earth. I think it is horrible that we have negatively affected Earth so quickly.           Questions I have are about the species lost in the mass extinction. How can scientists figure out the percentage of species lost?

In this unit , we covered how evolution works and how it has affected today ’ s Earth . Variation exists in all species , as it ’ s any difference in traits within a population . Charles Darwin made great contributions in understanding evolution with his four observations : sexually reproductive species have high genetic variation ; all species can produce more offspring than their environment can support ; traits are inherited from parents ; and not all offspring survives due to limited sources . Natural selection favors certain phenotypes , where the better phen/otypes survive . Speciation is the rise of two or more species from an existing one , through behavioral isolation or temporal isolation . Scientists have discovered evidence of evolution through embryology , vestigial structures , fossils , homologous structures , an