5.2 [ Paleontology, Radiometric Dating , Biogeography ]

     The earth is an ever changing ecosystem only the strongest species will survive. Before there was different land masses there use to be a combined land mass called Pangaea. Most evidence suggests that all modern species evolved from the ancestral species. We assume this from careful examination of fossils which is called Paleontology which is the study of fossils.  Fossils are made by minerals in water that seep through layers and layers of soil and into the bones of a animal that was burried and then replace the living tissue. Through radiometric dating and biogeography we can determine that many different species have lived on Earth, very few of today's species were even alive one million years ago. To put that into context the earth is about 4.5 billion years old. And almost all of those species are now extinct. At first the progression of species went from very basic single celled organisms to more complex multi-cellular organisms. Notably most living species in areas have similarities with fossisls found in the area suggesting that evolution took place.

      In 1903 radioactivity was discovered it was a source of heat energy. Radioactive decay also provides a form of a clock, giving scientists a mean to determine the age of the Earth. Radioactive decay changes a atom into an isotope of the same or different element. For example uranium 238 decays into lead 206  we call these decay rates called half-lives.The isotopes are not affected by temperature, moisture or any other environment conditions. With consistent half lives isotopes can be extraordinarily precise radiometric clocks. A technique used to determine the age of a rock or fossil is called radiometric dating. Biogeography is defined as the study of the geographic distribution of life on Earth, with biogeography we find clues to the history of life on Earth.Over 225 million years Earths landmasses have changed. The Earths tectonic plates eventually separated the landmasses we see today.So for example you may find dinosour remains in south america and also find the same type in Africa which suggets at one point the two continents were connected.


Ritter, B., Burley, K., & Fraser, D. (2007). Chapter 5 Evolution: Evidence of a Changing Earth., Biology (p. 140-143). Nelson. (Original work published 2007)

Roar. N.d. http://free-extras.com/images/roar-1750.htm. N.p., n.d. Web. 22 Apr.2011.