IN HIGH SCHOOLS | EDUCATOR GUIDE NASA April 15, 2017 How Earth Got its Moon April 15, 2017 EDUCATOR GUIDE How Earth Got its Moon About this Issue The article “How Earth got its moon” describes theories of how the Earth’s moon formed. Did it form as the result of a collision with a large protoplanet called Theia, or did multiple impacts create many mini moons that then merged over time? Computer modeling and isotopic analyses provide some data used to support or refute current theories. Scientists are still searching for other moon formation ideas and ways to test them. Students can focus on details in the article, follow connections to earlier articles about the origins of Earth’s moon, explore cross-curricular connections to other major science topics and calculate relevant lunar properties for themselves. Science News for Students provides another Connections version of this article written at a lower Lexile level (7.9 readability score): to Curricula: “How Earth got its moon.” Power Words are defined at the end of the cienceS History of the Earth News for Students article. Computer modeling Thermodynamics Want to introduce your students to an interesting STEM career related to this Geology article? Check out Cool Jobs: Probing Pluto by Science News for Students. Igneous rocks Solar system Women’s contributions to scientific endeavors, including planetary science, Asteroids and meteorites have been the subject of award-winning movies this year including Hidden Angular momentum Centrifugal/centripetal Figures, which focused on African-American mathematicians who were crucial acceleration to the first launch of an American into space orbit. Want to introduce your Gravitational acceleration students to some other women pursuing STEM careers? Check out “A woman’s Isotopes place is in science” in Science News for Students. What’s in this Guide? s Article-Based Observation: These questions focus on reading and content comprehension by draw- ing on information found in the article “How Earth got its moon.” Questions focus on ideas about the origin of Earth’s moon and evidence that supports multiple explanations of its formation. s Quest Through the Archives: With Internet access and your school’s digital access to Science News, your students can use this short section to explore other articles about our moon’s origin as reported by Science News since 1922. s Cross-Curricular Discussion: These questions and extension prompts connect to the article “How Earth got its moon” and encourage students to think in more detail about scientific areas related to the articles. The section is divided roughly by science subdiscipline for educators who would like to focus on one topic area. The extension prompts for each subdiscipline include some that are top- ic-specific and others that are more conceptually advanced. Earth and Space Sciences questions address types of rocks and minerals found on Earth, how they formed and how they might provide clues to the moon’s formation. Physical and Chemical Sciences questions involve defining isotopes and physical applications of measuring isotope ratios. Biological Sciences and Engineering ques- tions concern biomedical applications of certain isotopes and questions regarding isotopic measur- ing techniques and other applications. s Activity: Students can calculate the angular momentum and density of the moon and consider the implications of the results for various theories of the moon’s origin. Standards Alignment Next Generation Science Common Core Earth’s Place in the Universe: History of Earth: HS- ESS1-5, ELA Standards: Reading Informational Text (RI): 1, 2, 4, 5, 7 HS-ESS1-6 Motion and Stability: Forces and Interactions: HS-PS2-2, ELA Standards: Writing (W): 1, 2, 3, 4, 6, 7, 9 HS-PS2-3, HS-PS2-4 Matter and Its Interactions: HS-PS1-5, HS-PS1-8 ELA Standards: Speaking and Listening (SL): 1, 2, 4, 6 Engineering Design: HS-ETS1-2 ELA Standards: Reading for Literacy in Science and Technical Subjects (RST): 1, 2, 3, 4, 5, 7, 8, 9 ELA Standards: Writing Literacy in History/Social Studies and Science and Technical Subjects (WHST): 1, 2, 4, 6, 7, 9 April 15, 2017 IN HIGH SCHOOLS How Earth Got its Moon Article-Based Observation Directions: After reading the article “How Earth got its moon,” answer these questions: 1. What was the moon-formation idea proposed in the mid-1970s? 2. Why does the author describe Earth’s moon as an “oddball”? 3. A study in 2001 analyzed rocks collected during the Apollo mission to the moon. How did these lunar rocks support the hypothesis that the moon was formed by multiple impacts and contradict the giant-impact hypothesis? 4. What did planetary scientist Raluca Rufu and her colleagues learn recently that supports the multi-impact hypothesis? Explain how their findings support this hypothesis and why scientists were not able to figure this out previously. 5. According to planetary scientist Nicolas Dauphas, how does the isotopic combination of materials that make up Earth tell a story that supports the idea of a single impact? What does Dauphas say supplied the Earth’s mass? BLACKLINE MASTER 1, P. 1 6. Planetary scientist Sarah Stewart states that we need to test all the new ideas about the moon’s formation. Describe the recent test that used temperature to help explain how the moon formed, and explain which moon-formation idea is consistent with the results. 7. Explain the similarities and differences between the graphic titled “Making moons” and the com- puter simulation images shown below. R. CANUP/SWRI Making moons The multi-impact hypothesis says several small hits sent terrestrial materials into orbit that eventually formed our large moon. First Disk of debris Moonlet drifts Subsequent Disk formation Moonlets merge in impact forms outward impact far-out orbit (Repeat) Millions Days Centuries of years Days Centuries R. RUFU ET AL/NATURE GEOSCIENCE 2017 BLACKLINE MASTER 1, P. 2 April 15, 2017 EDUCATOR GUIDE How Earth Got its Moon Responses to Article-Based Observation 1. What was the moon-formation idea proposed in the mid-1970s? Possible student response: Scien- tists proposed the “giant-impact hypothesis.” According to this idea, a Mars-sized body called Theia collided with the Earth 4.5 billion years ago with such force that debris from both Earth and Theia was thrown into orbit, eventually combining to form the Earth’s moon. 2. Why does the author describe Earth’s moon as an “oddball”? Possible student response: Most of the solar system’s moons orbit gas giant planets that are farther away from the sun than Earth is. Earth’s moon is large compared with the moons of Mars, the only other terrestrial planet with moons. Mars’ moons are small enough to be asteroids that were caught by its gravity, but Earth’s moon is probably too big to have been captured by gravity. 3. A study in 2001 analyzed rocks collected during the Apollo mission to the moon. How did these lunar rocks support the hypothesis that the moon was formed by multiple impacts and contradict the giant-impact hypothesis? Possible student response: The 2001 study of lunar rocks shows that Earth and its moon have identical mixes of oxygen isotopes. If the moon was a mixture of material from the two planets, the moon’s composition should be different than Earth’s. 4. What did planetary scientist Raluca Rufu and her colleagues learn recently that supports the multi-impact hypothesis? Explain how their findings support this hypothesis and why scientists were not able to figure this out previously. Possible student response: When the proposal of multi- ple impacts was first suggested in 1989, the computer power needed to run the necessary simulations was not available. Recently, Rufu and colleagues designed a computer simulation of multiple impacts to Earth. In the simulation, impactors that hit Earth directly transferred energy deep into Earth, send- ing terrestrial material into space. This material combined over centuries to form small moons, and over roughly 100 million years, about 20 small moons merged to form one moon. 5. According to planetary scientist Nicolas Dauphas, how does the isotopic combination of materials that make up Earth tell a story that supports the idea of a single impact? What does Dauphas say supplied the Earth’s mass? Possible student response: Dauphas reported that most of the materi- al making up Earth comes from the same material as a single type of meteorite called an enstatite chondrite. The placement of different elements helped Dauphas develop a timeline showing when different types of space rocks added to the Earth’s mass. For example, iron-loving elements, such as ruthenium, sink deeper into the Earth’s crust. Therefore, any ruthenium near the Earth’s crust likely arrived later in the Earth’s development. The timeline shows that around three-fourths of Earth’s mass came from enstatite chondrite and its precursors. If Theia formed at the same approximate distance from the sun as Earth, its composition would be similar. 6. Planetary scientist Sarah Stewart states that we need to test all the new ideas about the moon’s formation. Describe the recent test that used temperature to help explain how the moon formed, and explain which moon-formation idea is consistent with the results. Possible student response: The moon’s isotopic abundances were compared with that of glasses formed by a nuclear blast. Due to the extremely high temperatures created by the blast, the glasses lacked light isotopes of zinc, which had been leached out. Lunar rocks did not have zinc isotopes either, suggesting they had been exposed to extreme temperatures. Both moon-formation ideas are consistent with this hypothesis. Scientists say that either one large impact or many smaller impacts could have caused high enough temperatures to leach the light zinc isotopes from the rock.