Grades 9-12 or Adult Sophisticated Learner
All life on this planet needs water to survive. Some life can live with very little water in extremely dry places but they still need water. As we strive to find life beyond Earth, it is important to consider what life on Earth tells us about where to look. Why is water so important for life? Water supports cell functions. All organisms are made of cells, from microbes to the largest animals. All of life’s functions are completed within cells. Life needs chemical reactions to take place in order to gain energy, grow, and get rid of waste. Water is a liquid which allows the chemistry of life to take place. It is also a polar molecule which allows most other molecules to be dissolved. Because of this, we call water a “solvent”. Having such a good solvent as water is critical for the functions of life. But there are also some other reasons why water is so important:
Water is plentiful! Hydrogen is the most plentiful element in the universe and oxygen the most plentiful in Earth’s crust. On Earth, about 70% of the surface is covered by water. But there’s also lots of water in other places in our solar system. For instance, we’ve found many lines of evidence that lots of water existed on the surface of Mars during its early times, and Mars currently has a lot of frozen water under its surface. Comets contain mostly water ice. There are lots of moons in our solar system that are made of a lot of water ice, and there are even some moons with liquid water oceans under their icy crusts (like Europa and Enceladus).
Water still has other advantages as a solvent for life. For instance, water stays in the liquid phase over a large range of temperatures compared to some other solvents. That allows more places to have the potential for liquid water. It also has a high heat capacity. This means that water offers some protection to organisms from quick or drastic temperature changes.
Water also has an interesting property with regard to the density of ice. For many molecules, the solid has a higher density than the liquid. So, for most molecules, the solid would sink in the liquid. But this isn’t the case with water. For water, ice is actually less dense than liquid water. This is why ice floats! If this didn’t happen, then all of the organisms that live in the bottoms of lakes in the winter time would be completely frozen. But, even worse, during times in our planet’s history when the world has become very cold (causing what we call Snowball Earth), if frozen water sank, then all of Earth’s ocean life would have become frozen and maybe died!
If we want to understand how life works, then it’s really important to understand the chemistry of water. And astrobiologists who are wondering if we’re alone in the universe need to be aware of the potential for water to be important for other kinds of life as well. Right now, we’re investigating worlds like Enceladus and Europa, Mars, and other solar system bodies that show signs of water. Also, beyond our solar system, we’re looking for exoplanets that have the potential for liquid water at their surfaces, since they might be important places for us to look for possible extraterrestrial life.
Disciplinary Core Ideas
PS3.A: Definitions of Energy: Motion energy is properly called kinetic energy; it is proportional to the mass of the moving object and grows with the square of its speed. (MS-PS3-1) ▪A system of objects may also contain stored (potential) energy, depending on their relative positions. (MS-PS3-2) Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. (MS-PS3-3, MS-PS3-4)
PS3.D: Energy in Chemical Processes and Everyday Life: The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i.e., from sunlight) to occur. In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen. (MS-LS1-6)
LS2.C: Ecosystem Dynamics, Functioning, and Resilience: Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health. (MS-LS2-5)
ESS2.A: Earth’s Materials and Systems: All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the Sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms. (MS-ESS2-1)
ESS2.C: The Roles of Water in Earth’s Surface Processes: Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land. (MS-ESS2-4) ▪ Global movements of water and its changes in form are propelled by sunlight and gravity. (MS-ESS2-4)
ESS3.A: Natural Resources: Humans depend on Earth’s land, ocean, atmosphere, and biosphere for many different resources. Minerals, fresh water, and biosphere resources are limited, and many are not renewable or replaceable over human lifetimes. These resources are distributed unevenly around the planet as a result of past geologic processes. (MS-ESS3-1)
ESS2.D: Weather and Climate: Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns. (MS-ESS2-6) The ocean exerts a major influence on weather and climate by absorbing energy from the Sun, releasing it over time, and globally redistributing it through ocean currents. (MS-ESS2-6)
Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable. (HS-ESS2-7)
Big Ideas: All living things need water. Water is critical to cellular function, chemical reactions, and thermal regulation. Water is less dense when a solid and stays in the same state over a wide temperature range. It is abundant on Earth and a common thread between all living things. Water has been found in other places beyond Earth, like Mars and meteorites. Because water is so universal, Astrobiologist look for water on the surface and atmosphere of exoplanets as an indicator that the planet could support life. Understanding the chemistry of water is important to understanding how life works.
Boundaries: In this grade band, students investigate the properties of water and its effects on Earth materials and surface processes including chemical investigations like chemical weathering and recrystallization. (HS-ESS2-5)
5-12 Astrobiology Graphic Histories. Issue 5: Astrobiology and the Earth. These astrobiology related graphic books are ingenious and artfully created to tell the story of astrobiology in a whole new way. The complete series illustrates the backbone of astrobiology from extremophiles, to exploration within and beyond the solar system. This issue explains how astrobiologists explore analog environments on Earth in order to better understand environments that could support life on other worlds like Mars. Studying Earth is key to understanding life’s potential in the universe. NASA. https://astrobiology.nasa.gov/resources/graphic-histories/
6-12 Big Picture Science: Rife with Life. “Follow the water” is the mantra of those who search for life beyond Earth. Where there’s water, there may be life. This podcast features a tour of watery solar system bodies that hold promise for biology: Europa, Enceladus, Mars & Titan. SETI scientist Seth Shostak hosts this radio show on various topics in science, cosmology, physics, astronomy and astrobiology. Shostak interviews experts and explains important discoveries and concepts including in his weekly 50-minute shows. http://www.bigpicturescience.org/episodes/Rife_with_Life and http://www.bigpicturescience.org/Astrobiology_Index
6-12 Astrobiology Math. This collection of math problems provides an authentic glimpse of modern astrobiology science and engineering issues, often involving actual research data. Students explore concepts in astrobiology through calculations. Relevant topics include Ice or Water? (page 49) and Ice to Water…The Power of a Little Warmth! (page 51). NASA. https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf
6-12 (3-5 adaptable) Project Spectra! – Planet Designer: Kelvin Climb. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Kelvin Climb” students create a planet using a computer game and change features of the planet to increase or decrease the planet’s temperature. Students explore some of the same principles scientists use to determine how likely it is for a planet to maintain flowing water, a critical ingredient for life as we know it. Using computer simulation is a powerful tool in the search for life and the conditions for life in the solar system and beyond. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/KelvinClimb_teacher_20130617.pdf
6-12 (3-5 adaptable) Project Spectra! Planet Designer: Retro Planet Red. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Retro Planet Red” students learn about Mars’ past and present before exploring the pressure and greenhouse strength needed for Mars to have a watery surface as it had in the past. Water is a key ingredient for life. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/Retro_Planet_Red_teacher_20130617.pdf
8-10 SpaceMath Problem 275: Water on the Moon! Students estimate the amount of water on the moon using data from Deep Impact/EPOXI and NASA’s Moon Mineralogy Mapper experiment on the Chandrayaan-1 spacecraft. [Topics: geometry, spherical volumes and surface areas, scientific notation] https://spacemath.gsfc.nasa.gov/moon/6Page11.pdf
8-10 SpaceMath Problem 264: Water on Planetary Surfaces. Students work with watts and Joules to study melting ice. [Topics: unit conversion, rates] https://spacemath.gsfc.nasa.gov/astrob/Astro3.pdf
8-10 SpaceMath Problem 121: Ice on Mercury? Since the 1990’s, radio astronomers have mapped Mercury. An outstanding curiosity is that in the polar regions, some craters appear to have ‘anomalous reflectivity’ in the shadowed areas of these craters. One interpretation is that this is caused by subsurface ice. The MESSENGER spacecraft hopes to explore this issue in the next few years. In this activity, students measure the surface areas of these potential ice deposits and calculate the volume of water that they imply. [Topics: area of a circle; volume, density, unit conversion] https://spacemath.gsfc.nasa.gov/planets/4Page23.pdf
9-12 SpaceMath Problem 338: Asteroids and Ice. Students calculate how much ice may be present on the asteroid 24-Themis based on recent discoveries by NASA [Topics: mass=density x volume; volume of a spherical shell] https://spacemath.gsfc.nasa.gov/astrob/6Page154.pdf
9-12 SpaceMath Problem 287: LCROSS Sees Water on the Moon. Students use information about the plume created by the LCROSS impactor to estimate the (lower-limit) concentration of water in the lunar regolith in a shadowed crater. [Topics: geometry; volumes; mass=density x volume] https://spacemath.gsfc.nasa.gov/moon/6Page66.pdf