 Challenge  How long have organisms been living on Earth? Key Vocabulary:  Geologic Time Scale  Radiometric Dating  Mass Extinction Activity 92: Time for Change

 ON the first day of school, how do you know when to go to each of your classes??  Scientists have broken Earth’s history into distinct sections of time, with each section defined by different characteristics  Geologic Time Scale  categorizes and divides the history of Earth into a series of consecutive sections that are organized by periods of time Geologic Time Scale

 Radiometric Dating  the analysis of certain minerals that contain radioactive elements, which over time decay into different elements. (This gives us ages of rocks/fossils)  Mass Extinction  High rates of extinction for many species in a relatively short geologic time span.

 Volcanic eruptions  Tectonic activity  Global cooling/warming  Meteor strikes  The Earth has had 5 major mass Extinctions!!! Reasons for Mass Extinction:

 We estimate the Earth to be about 4.5 billion years old  That is a lot of time!! Think about how much has changed in the last decade! How old is the Earth??

 We are going to investigate your own history and construct a personal time scale.  Begin Part One of the Procedure (page F-17) and stop at Step 6 Glue in Student Sheet 92.1

 Put your 6 Fossil Cards in order. Follow Procedure Steps 7-10  Glue in Student Sheet 92.2  Use the chart to construct your Geologic Timeline:  Follow Step 11 Part 2

 Geologic Event Time Cards – Follow Steps 14 and 15  When you are finished, Answer Analysis Question 4 with your group and record your answers in your notebook. Mass Extinctions