5.3. How did life become something that competes for resources and evolves?

We know that evolution is how life adapts to its environment over time. This adaptation is driven by variability and by competition within populations of organisms. Evolution allows for the most successful traits within a population to continue on through reproduction. We have good reason to think that this process of selection for certain traits has been around for as long as living things and maybe even before that. It’s possible that the evolution of chemical systems was one necessary step in the origin and development of life on Earth. If that’s the case, where do you think these early evolving systems might have been found?

Since we know water is such an important solvent for life, many have considered whether the first evolving chemical systems developed in “warm little ponds” or in tide pools or maybe around hydrothermal vents or in hot springs. These kinds of places have water as well as ways of concentrating molecules together and providing energy sources from sunlight or from heat. We also need to consider how some early chemical reactions may have been catalyzed: that is, were there molecules or maybe minerals present that caused chemical reactions to happen? Clays and some kinds of minerals might have been good at doing this. There are also some molecules that act as natural catalysts. For instance, RNA (ribonucleic acid) is a molecule that’s a lot like DNA (deoxyribonucleic acid), but it’s often just single-stranded (DNA is double-stranded) and we now know that RNA can catalyze reactions like those that form bonds between amino acids to turn them into proteins.

It’s important for the scientists who study these questions to consider the environments on the early Earth and possible reactions that could have happened then as well as to look at how life functions in our modern world. While some people are working in labs to better understand cellular functions and how life catalyzes reactions in different environments, there are other researchers who are studying old rocks to better understand what the chemical and physical environment of the early Earth’s surface was. If we want to better understand how life may have gone from an evolving chemical system to the great diversity of living, evolving things that we see today, then we need people from a lot of different scientific backgrounds to work together to put together the pieces of the puzzle.

Disciplinary Core Ideas

LS1.A: Structure and Function: All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1) ▪ Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)

LS2.B: Cycle of Matter and Energy Transfer in Ecosystems: Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem. (MS-LS2-3)

LS4.A: Evidence of Common Ancestry and Diversity: The collection of fossils and their placement in chronological order (e.g., through the location of the sedimentary layers in which they are found or through radioactive dating) is known as the fossil record. It documents the existence, diversity, extinction, and change of many life forms throughout the history of life on Earth. (MS-LS4-1) ▪ Anatomical similarities and differences between various organisms living today and between them and organisms in the fossil record, enable the reconstruction of evolutionary history and the inference of lines of evolutionary descent. (MS-LS4-2)

LS4.B: Natural Selection: Natural selection leads to the predominance of certain traits in a population, and the suppression of others. (MS-LS4-4)

LS4.C: Adaptation: Adaptation by natural selection acting over generations is one important process by which species change over time in response to changes in environmental conditions. Traits that support successful survival and reproduction in the new environment become more common; those that do not become less common. Thus, the distribution of traits in a population changes. (MS-LS4-6)

ESS1.C: The History of Planet Earth: The geologic time scale interpreted from rock strata provides a way to organize Earth’s history. Analyses of rock strata and the fossil record provide only relative dates, not an absolute scale. (MS-ESS1-4)

PS1.A: Structure and Properties of Matter: Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. (MS-PS1-1, MS-PS1-2)

PS1.B: Chemical Reactions: Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-3, MS-PS1-2, MS-PS1-5)

LS1.C: Organization for Matter and Energy Flow in Organisms: Plants, algae (including phytoplankton), and many microorganisms use the energy from light to make sugars (food) from carbon dioxide from the atmosphere and water through the process of photosynthesis, which also releases oxygen. These sugars can be used immediately or stored for growth or later use. (MS-LS1-6) ▪ Within individual organisms, food moves through a series of chemical reactions in which it is broken down and rearranged to form new molecules, to support growth, or to release energy. (MS-LS1-7)

LS2.A: Interdependent Relationships in Ecosystems: Organisms, and populations of organisms, are dependent on their environmental interactions both with other living things and with nonliving factors. (MS-LS2-1) ▪ In any ecosystem, organisms and populations with similar requirements for food, water, oxygen, or other resources may compete with each other for limited resources, access to which consequently constrains their growth and reproduction. (MS-LS2-1)

LS2.C: Ecosystem Dynamics, Functioning, and Resilience: Ecosystems are dynamic in nature; their characteristics can vary over time. Disruptions to any physical or biological component of an ecosystem can lead to shifts in all its populations. (MS-LS2-4)

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) ▪ Cellular respiration in plants and animals involve chemical reactions with oxygen that release stored energy. In these processes, complex molecules containing carbon react with oxygen to produce carbon dioxide and other materials.

Crosscutting Concepts

Cause and Effect: Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability. (MS-LS4-4, MS-LS4-6)

Big Ideas: The process of evolution relies on the survival of the fittest organisms best suited to their environment. While the origin of life on Earth is yet unknown, there are certain areas that are more likely than others. Astrobiologists study life living in these possible locations to better understand how life formed and the likely conditions it formed under. Places that have water, ways of concentrating molecules, and a source of energy are of particular interest.

Boundaries:: Students in this grade band use mathematical representations to support explanations of natural selection over time. Emphasis is on using mathematical models, probability statements, and proportional reasoning to support explanations of trends in changes to populations over time. Does not include Hardy Weinberg calculations. (MS-LS4-6)

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 Exploring Archean Life Forms (page 23) and The Evolution of Nucleotides and Genes (page 19) where students explore concepts in science through calculations. NASA. https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf

6-12 Origins: Life on Earth. In this web interactive, South Africa’s ancient rocks give clues about the earliest life on Earth. Video, pictures, and print weave information for the learner as they more deeply understand the scientific pursuit of astrobiology. UW-Madison. https://origins.wisc.edu/chapter-1-the-universe/

6-12 Origins: Humankind. In this web interactive, scientists and students dive deep underground to connect with our evolutionary past. Video, pictures, and print weave information for the learner as they more deeply understand the scientific pursuit of astrobiology. UW-Madison. https://origins.wisc.edu/

We know that evolution is how life adapts to its environment over time. This adaptation is driven by variability and by competition within populations of organisms. Evoluation allows for the most successful traits within a population to continue on through reproduction. The most successful traits aren’t always the ones that might seem to be the best. We have good reason to think that this process of selection for certain traits has been around for as long as living things and maybe even before that. It’s possible that the evolution of chemical systems was one necessary step in the origin and development of life on Earth that preceded even the development of cells. If that’s the case, where do you think these early evolving systems might have been found?

Since we know water is such an important solvent for life, many have considered whether the first evolving chemical systems developed in “warm little ponds” or in tide pools or maybe around hydrothermal vents or in hot springs. These kinds of places have water as well as ways of concentrating molecules together and providing energy sources from sunlight, from motion (like waves or tides), or from heat. We also need to consider how some early chemical reactions may have been catalyzed: that is, were there molecules or maybe minerals present that caused chemical reactions to happen? Clays and some kinds of minerals might have been good at doing this. There are also some molecules that act as natural catalysts. For instance, RNA (ribonucleic acid) is a molecule that’s a lot like DNA (deoxyribonucleic acid), but it’s often just single-stranded (DNA is double-stranded), and we now know that RNA can catalyze reactions like those that form bonds between amino acids to turn them into proteins. Forming these bonds, known as peptide bonds, and making proteins is something that RNA does inside of our own cells today. Not only can RNA catalyze reactions, but it also acts as an information storage molecule and might have been the primary source for carrying information before DNA existed. This has led some scientists to propose that a so-called “RNA World” existed early in the history of life, where RNA was acting as a catalyst and information carrier for all (or at least most) of the living things that existed at that time. However, even getting to an RNA World would have required a lot of steps in the processes of chemical evolution, and these are steps that we’re still trying to learn more about today.

It’s important for the scientists who study these questions to consider the environments on the early Earth and possible reactions that could have happened then as well as to look at how life functions in our modern world. While some people are working in labs to better understand cellular functions and how life catalyzes reactions in different environments, there are other researchers who are studying old rocks to better understand what the chemical and physical environment of the early Earth’s surface was. If we want to better understand how life may have gone from an evolving chemical system to the great diversity of living, evolving things that we see today, then we need people from a lot of different scientific backgrounds to work together to put together the pieces of the puzzle.

Disciplinary Core Ideas

LS1.A: Structure and Function: Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1) All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (HS-LS1-1)

LS2.A: Interdependent Relationships in Ecosystems: Ecosystems have carrying capacities, which are limits to the numbers of organisms and populations they can support. These limits result from such factors as the availability of living and nonliving resources and from such challenges such as predation, competition, and disease. Organisms would have the capacity to produce populations of great size were it not for the fact that environments and resources are finite. This fundamental tension affects the abundance (number of individuals) of species in any given ecosystem. (HS-LS2-1, HS-LS2-2)

LS2.B: Cycles of Matter and Energy Transfer in Ecosystems: Photosynthesis and cellular respiration (including anaerobic processes) provide most of the energy for life processes. (HS-LS2-3) ▪ Photosynthesis and cellular respiration are important components of the carbon cycle, in which carbon is exchanged among the biosphere, atmosphere, oceans, and geosphere through chemical, physical, geological, and biological processes. (HS-LS2-5)

LS2.C: Ecosystem Dynamics, Functioning, and Resilience: A complex set of interactions within an ecosystem can keep its numbers and types of organisms relatively constant over long periods of time under stable conditions. If a modest biological or physical disturbance to an ecosystem occurs, it may return to its more or less original status (i.e., the ecosystem is resilient), as opposed to becoming a very different ecosystem. Extreme fluctuations in conditions or the size of any population, however, can challenge the functioning of ecosystems in terms of resources and habitat availability. (HS-LS2-2, HS-LS2-6)

LS4.A: Evidence of Common Ancestry and Diversity: Genetic information provides evidence of evolution. DNA sequences vary among species, but there are many overlaps; in fact, the ongoing branching that produces multiple lines of descent can be inferred by comparing the DNA sequences of different organisms. Such information is also derivable from the similarities and differences in amino acid sequences and from anatomical and embryological evidence. (HS-LS4-1)

LS4.B: Natural Selection: Natural selection occurs only if there is both (1) variation in the genetic information between organisms in a population and (2) variation in the expression of that genetic information — that is, trait variation — that leads to differences in performance among individuals. (HS-LS4-2, HS-LS4-3) ▪ The traits that positively affect survival are more likely to be reproduced, and thus are more common in the population. (HS-LS4-3)

LS4.C: Adaptation: Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline – and sometimes the extinction – of some species. (HS-LS4-6)

PS2.B: Types of Interactions: Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. (HS-PS2-6)

PS3.D: Energy in Chemical Processes: The main way that solar energy is captured and stored on Earth is through the complex chemical process known as photosynthesis

Crosscutting Concepts

Patterns: Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. (HS-LS4-1, HS-LS4-3)

Big Ideas: The process of evolution relies on the survival of the fittest organisms best suited to their environment. While the origin of life on Earth is yet unknown, there are certain areas that are more likely than others. The process of the formation of life on Earth is also largely unknown but was likely a complex process that took place over a long period of time. For the earliest forms of life to begin, complex molecules, organic materials, a source of energy, and a suitable environment were all necessary. Scientists study geochemical pathways to possibly understand early life on Earth. In a proposed “RNA” world, RNA acted as a catalyst and information carrier for early living things that existed.

Boundaries: Students in this grade band use data to provide evidence for specific biotic and abiotic differences ecosystems contribute to a change in gene frequency over time, leading to adaptation. (HS-LS4-4) Assessment is limited to basic statistical and graphical analysis. (HS-LS4-3)

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 Exploring Archean Life Forms (page 23) and The Evolution of Nucleotides and Genes (page 19) where students explore concepts in science through calculations. NASA. https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf

6-12 Origins: Life on Earth. In this web interactive, South Africa’s ancient rocks give clues about the earliest life on Earth. Video, pictures, and print weave information for the learner as they more deeply understand the scientific pursuit of astrobiology. UW-Madison. https://origins.wisc.edu/chapter-1-the-universe/

6-12 Origins: Humankind. In this web interactive, scientists and students dive deep underground to connect with our evolutionary past. Video, pictures, and print weave information for the learner as they more deeply understand the scientific pursuit of astrobiology. UW-Madison. https://origins.wisc.edu/

9-12 Exploring Life’s Origins: Understanding the RNA World. Through video clips, illustrations, animation and interactives students can explore RNA, ribozymes, and the RNA world. The RNA world hypothesis holds that earlier forms of life may have relied solely on RNA to store genetic information and to catalyze chemical reactions. An educator resource guide is included. NSF. http://exploringorigins.org/rnaworld.html

10-12 The Rules of Life. This podcast covers how to predict the phenotype, structure, function and behavior of an organism, based on what we know about its genes and environment. If we can identify some of the basic rules of life across scales of time, space and complexity, we may be able to predict how cells, brains, bodies and biomes respond to changing environments. NSF. https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=242752&WT.mc_id=USNSF_1