Section 5.2 Evidence of a Changing Earth Chapter 5 Section 5.2 Evidence of a Changing Earth

Puzzle pieces Do they fit together? What do the pieces remind you of?

Video Earth moving: http://www.youtube.com/watch?v=cQVoSyVu9rk Open up the front page of your textbook Tectonic plates: http://www.youtube.com/watch?v=Cm5giPd5Uro follow along in textbook & discuss stages

What’s with the Opossum ? What’s an opossum? What’s a marsupial? It is the only marsupial on North America… all the rest are hanging out on Australia How did that happen???

Evidence of a Changing Earth Although it is impossible to directly observe what Earth was like millions of years ago, indirect evidence suggests that the types of organisms that lived in the past were very different from those today. The evidence comes from a variety of sources: fossil records, the geographic distribution of species, comparative anatomy and embryology, behaviour, breeding and biochemistry and genetics.

Evidence from Fossils Paleontology is the study of fossils. Fossilized remains, impressions and traces of organisms provide scientists with direct physical evidence of past life.

Burgess Mountain

Burgess Shale

What’s so special about it? http://www.burgess-shale.bc.ca/

Fossils from the Precambrian Called Edicarian fauna http://www.youtube.com/watch?v=ice47loNmsc

3 patterns have become evident from this rock: Different species lived on Earth at various times in the past. Very few of today’s species were alive 1 million years ago, and almost all of the species that have lived are now extinct.

2. The complexity of living organisms generally increases from the most distant past to the present. When fossil deposits are arranged from most ancient to most recent, there is an obvious and systematic progression from only very simple organisms to more complex species.

3. Living species and their most closely matching fossils are typically located in the same geographic region. For example, all fossils of ancient sloths are found in Central and South America, the only region in which modern, but smaller and very different species of sloth live today.

Dating the Past Radiometric dating – a technique used to determine the age of a rock or fossil. Radioactive decay can provide scientists with a means to determine the absolute age of the Earth with great precision. Radioactive decay changes a particular atom (parent isotope) into a daughter isotope of the same or a different element. Ex. Radioactive potassium 40 decays to become argon 40 or calcium 40. Ex. Uranium 238 decays into lead 206.

Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Ex. Carbon 12, Carbon 13, and Carbon 14. They are all carbon atoms but one has 6 neutrons,7 neutrons and 8 neutrons, respectively. Physicists measure these decay rates in units called half-lives, or the amount of time it takes for half of a sample of the isotope to decay.

Ex. An organism contains carbon 14. When the organism dies the carbon 14 begins to turn into nitrogen 14. If the half-life of carbon 14 is 5000 years then when half the carbon 14 has transformed into nitrogen 14, 5000 years have passed or 1 half life. If now only ¼ of the original carbon 14 is remaining and ¾ of it is nitrogen 14 another half life is passed. And if 2 half lives have now passed, then the organism has now been dead for 10 000 years. (5000 + 5000). This is how the scientists can figure out the exact number of years an organism has been dead, by comparing the amount of the original isotope to the new isotope.

Evidence from Biogeography Biogeography – is the study of the geographic distribution of life on Earth. Our landmasses on Earth began as one big continent called Pangaea. Over the years our land masses have broken up into the continents we now see.

Pangaea

After the continents separated, most species younger than about 150 million years were restricted to separate continents. Most recent fossils of the same species are only found on similar continents. This strongly suggests they evolved after the breakup of the continents.