Tuesday 5/3/11 How the Earth Was Made

Content Objectives 1.We will learn about how scientists have determined the age of the Earth. 2.We will learn about the history of Earth over time.

Language Objectives 1.We will use reading, discussion and writing to learn about the history of Earth.

Schedule Agenda, objectives 5 min. Intro. to geologic methods for dating rocks 10 min. Video 25 min. Discussion 10 min.

How do scientists KNOW things? Observations Experiments Inferences

Relative Dating (this rock is older than that rock) Most of the time the rocks on the top are older than the rocks on the bottom

Absolute Dating (this rock is 28 million years old) Some atoms are not stable—they break down into “daughter” atoms Ex.: Uranium changes into a form of lead at a constant known rate

Oldest Rock Oldest rocks on Earth are the Acasta Gniess of northern Canada 4.03 billion years old © NASA Acasta Gneiss Zircon mineral

Oldest Zircon Grain 4.4 by zircon grain © NASA Ancient mineral grain found at Jack Hills, Australia Mineral grain eroded from first crust and then deposited in a new rock Dates the Earth’s first crust to around 4.4 billion years

Meteorites Radiometric age of meteorites date the formation of the Solar System and Earth (4.55 billion years old) en.wikipedia.org/wiki/Image:Canyon-diablo-meteorite.jpg Crab Nebula Canyon Diablo meteorite