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SIO 40

Fall 2021

Homework 1 Due Wednesday, October 6th

SUBMIT VIA Canvas (.pdf or .doc)

This homework covers materials presented in lectures 1,2, 3, 4 and 5. These are primarily short answer questions. Be careful to answer each part of multi-part questions. No handwritten answers, please.

1. (2 points total) Observations of changing climate (see https://climate.nasa.gov/, click on the links at the bottom of the page to answer the questions). a. Global temperature: 19 of the 20 warmest years on record have occurred since 2000. What year ranks as the warmest on record? (1 point) 2020 ranks as the warmest on record at 1.02 °C according to the data on this chart published by NASA at the following link: https://climate.nasa.gov/vital-signs/global-temperature/. However, according to the NASA article “2020 Tied for Warmest Year on Record, NASA Analysis Shows,” 2020 is tied with 2016 as warmed on record due to a small margin of error of the analysis, which would mean the recorded temperature of 1.01 °C in 2016 (according to the data from the same chart for the year 2020) ranks 2020 and 2016 as the warmest years on record since 2000 when considering that margin of error. b. Land ice: Earth’s polar ice sheets are losing mass. Which ice sheet is losing mass faster, Greenland or Antarctica? (1point) Greenland is losing mass faster than Antarctica with an average loss rate of 279 billions tons of ice per year, whereas Antarctica is losing mass at a slower rate at 148 billion tons of ice per year, according to NASA data. 2. (2 points total) Carl Sagan stated that “We ourselves are made of Stardust.” a. Where are elements formed? (1 point) Elements like hydrogen and helium were formed in stars during a process called nuclear fusion, elements may be formed. Iron can make a star unstable, it can trigger a supernova where the explosion of this abundance of elements that have accumulated in the star will release. b. How is the abundance of different elements in our bodies similar to the abundance of different elements in the universe? (1 point) Our bodies are made up largely of lighter elements like carbon, hydrogen, oxygen, and nitrogen. The abundance of these elements reflects the relative abundance of these elements in both the Earth and universe 2was these elements have to be available in large amounts in order to support living matter. 3. (2 points total) The moon a. What is the “Giant Impact Hypothesis” to explain the formation of Earth’s moon? (1 point) The “Giant Impact Hypothesis” describes a theory where a rock, Theia, hit Earth about 4.5 billion years ago, causing a disk of debris to orbit around the Earth. The debris then coalesced into the moon. However, it has more recently been theorized that Theia impacted the Earth not just once but twice before coalescing into the moon. b. At what point in Earth’s history is the moon thought to have formed? (i.e. how long ago?) (1 point) The moon was thought to have been formed 4527 Ma, or around 4.5 billion years ago. 4. (2 points total) In the search for extraterrestrial planets that may be capable of supporting life, scientists focus on particular characteristics. a) Define the “Habitable Zone” of a star. (1 point) The “Habitable Zone” is the distance from a star which temperatures are adequate enough (not too cold nor too hot) to support liquid water and ultimately support life.

b) How does the atmospheric composition of a planet impact its potential “habitability”? (1 point) A planet’s potential “habitability” is determined by the presence of greenhouse gasses and the distance the planet is from the star, factors affecting temperatures and the containment of heat. 5. (2 points total) Molecules important to origins of life theories: a) What molecules was Stanley Miller trying to create in his famous experiment? (1 point) Miller was trying to create amino acids. b) Ribosomes are ancient molecular machines that assemble proteins. What component of the ribosome catalyzes protein assembly and serves as a focal point for origins of life theories? (1 point) RNA catalyzes the process for protein assembly. 6. (2 points total) Stromatolites a) What are stromatolites? (1 point) Stromatolites are ancient life forms of bacteria layered in sediment. b) What do stromatolites tell us about when life appeared on Earth? (1 point) Stromatolites are ancient forms of life and the oldest fossil records on Earth, appearing up to 3.5 billion years ago. 7. (2 points total) Very early in Earth’s history, a “methane haze” atmosphere is thought to have existed. a) What was producing methane at this time? (1 point) Methanogens (methanogenic bacteria) were the archaea at the time producing methane through redox reactions. b) How did scientists use the carbon isotope signature of methane trapped in ancient rocks to identify the source of methane production? (1 point) Scientists knew that methanogens preferred to use carbon 12 rather than carbon 13 since it was the lighter isotope. When the scientists were examining the signatures in these ancient rocks, and would notice a depletion signature of carbon 13 and a signature of the light isotope carbon 12, they concluded that those rocks had methane that must have been produced through methanogenesis because methanogens preferred carbon 12. 8. (2 points total) Describe banded iron formations (BIFs) : a) What are they made of? (0.5 point) Banded iron formations are a type of sedimentary rock that’s made up of alternating layers of iron and silicate minerals. b) When did they form? (0.5 point) Radiometric dating tells us that the sediment was formed earlier than 1.9 billion years ago. c) What form of iron reacted with O2 in seawater to produce BIFs? (0.5 point) reacted with O2 in seawater to produce BIFs. d) Besides BIFs, what other types of sedimentary iron deposits are used as tracers (proxies) for the rise of atmospheric O2? (0.5 point)

Redbeds are ancient sedimentary formations that contain oxidized forms of iron, dating back to 2.2 billion years ago, providing a tracer for the rise of atmospheric O2 around that time. Pyrite is a form of reduced iron, whose deposits signal that atmospheric oxygen may not have been abundant at the time. 9. (2 points total) Stratospheric Ozone: a) What important function does stratospheric ozone perform? (0.5 point) The ozone shields the Earth from harmful ultraviolet radiation. b) Briefly describe in general terms how ozone is naturally produced in the stratosphere. (1 point) As O2 levels increase, so does ozone (O3), because O2 produces when it collides with UV. The free O atoms now collide with O2 molecules to make ozone O3. c) When did atmospheric ozone concentrations become significant? (0.5 point) Atmospheric ozone concentrations became significant about 1.9 billion years ago when shielding of UV became effective. 10. (2 points total) Relationships between atmospheric O2 and organic carbon: a) What is the simplified photosynthesis reaction? (0.5 point) CO2 + H20  CH2O + O2, or there is the “plant in a box” model with the equation CO2 + H2O = plant biomass + O2 b) From this reaction, what is also produced when organic matter is formed? (0.5 point) Oxygen is also produced when organic matter is formed. c) From (a) and (b), what important biological process prevents accumulation of atmospheric O 2? (0.5 point) The respiration of organic matter balances out what would otherwise be a constant increase of atmospheric O2. d) In certain periods during earth's history lots of organic matter was quickly produced by photosynthetic organisms, and preserved in sediments. How would this process impact atmospheric O 2 concentrations? (0.5 point) An increase of organic matter implies increase of respiration, therefore atmospheric concentrations of O2 would need to increase to ensure balance....