Tuesday, Sept 12, 2017 OBJ: SW examine geologic time WU: What does it take to become a fossil? Agenda: Laetoli Footprints video with discussion questions (2nd and 5th only) https://mpt.pbslearningmedia.org/resource/tdc02.sci.life.evo.laetolifoot/laetoli- footprints/#.Wbe_RsiGO1t Fossil Dating with video clip https://mpt.pbslearningmedia.org/resource/tdc02.sci.phys.matter.radiodating/radiometric- dating/#.Wbe_-8iGO1u Design your own cube. HW: Finish reading the Extinction over Time Article and complete the remaining questions. (Due on Thursday, Sept 13)

Laetoli Footprints (lay tolli) What was the unusual series of circumstances that caused the Laetoli footprints to be preserved? Does this combination of events say anything about why such footprints are a rare find? What do the footprints at Laetoli tell scientists about the way the creatures that made them moved? The Laetoli footprints were formed and preserved by a chance combination of events—a volcanic eruption, a rainstorm, and another ashfall. When they were found in 1976, these hominid tracks, at least 3.6 million years old, were some of the oldest evidence then known for upright bipedal walking, a major milestone in human evolution. 

Laetoli Footprints The Laetoli footprints were formed and preserved by a chance combination of events—a volcanic eruption, a rainstorm, and another ashfall. When they were found in 1976, these hominid tracks, at least 3.6 million years old, were some of the oldest evidence then known for upright bipedal walking, a major milestone in human evolution. 

Dating Fossils Before we answer this question— How do you know how old you are? How does a vet know how old a stray dog is? How do forensic scientists know how long a body has been dead? KEY COMPONENT Using EVIDENCE we collect to compare it to information we know to be accurate. When dating fossils, scientists rely on the information they know about ATOMS. (You learned in 6th grade that atoms make up everything– including fossils).

Atoms as Evidence of Age Atoms behave in a predictable manner. The three main parts of an atom are protons, neutrons, and electrons. This evidence does not depend on a chemical reaction, just how an atom works. With experience, we can predict how an atom behaves over time.

Atomic Clocks An atomic clock keeps perfect time by predictable behavior of electrons. Atomic clocks are designed to measure the precise length of a second. The International System of Units (SI) defines 1 sec = 9,192,631,770 oscillations of Cs-133 atom (In other words, the time taken by a particular wavelength of light emitted by a Cs-133 atom to execute 9,192,631,770 vibrations) Several atomic clocks in the world– including one at the  United States Naval Observatory in Washington DC

Radioactive Clocks These clocks use nuclear reactions to monitor changes in time. When atoms undergo a nuclear reaction, they changes from one type of atom to another. Examples: K-40 Ar-40 Rb-87  Sr-87 U-238  Pb-206 Because these process take a long time to occur they are used for geologic dating (long periods of time). Calvert Cliffs Nuclear Power Plant

Radiometric Dating What is radiometric dating? What elements are used? How old has scientists determined the earth to be?

Recap: 1)Introduction activity: Do fossils give us the whole picture? 2) Mr. Parr's Fossil Song 3) Becoming a fossil video with discussion questions 4) Laetoli Footprints video with discussion questions 5) Dating Fossils HW: Finish reading the Extinction over Time Article and complete the remaining questions. (Due on Thursday, Sept 13)