Shaping Each Other: Earth and Life Co-evolution Quiz

If biological processes alter the chemical composition of the environment, and if those environmental changes then drive natural selection, then the physical Earth and life are in a continuous, reciprocal relationship known as co-evolution.

If the early Earth was dominated by volcanic gases like CO2 and N2, and if free oxygen is highly reactive and would quickly disappear without a source, then oxygen could only accumulate once biological photosynthesis evolved to produce it.

If oxygenic photosynthesis requires a specific metabolic pathway, and if cyanobacteria were the first organisms to develop this pathway roughly 2.4 billion years ago, then they are the primary cause of the Great Oxidation Event.

If the early oceans contained high amounts of dissolved ferrous iron (Fe^2+), and if cyanobacteria began releasing oxygen, then the oxygen would react with the iron to form insoluble iron oxides; if these oxides settled on the sea floor, they formed the layers we see in the geological record.

If life produces oxygen, it enables the ozone layer; if marine life makes calcium carbonate, it forms limestone; if plants break down rocks, they accelerate weathering; and if life sequesters carbon, it reduces CO2.

If land plants increased the total global rate of photosynthesis and increased rock weathering, then they significantly removed CO2 from the air; if CO2 decreased while oxygen production rose, the atmosphere shifted toward its modern composition.

If methanogens in the Archean produced methane and later photosynthetic organisms removed CO2, then life has influenced the "thermostat" of the planet; if this prevented Earth from freezing or boiling, then life helped maintain the presence of liquid water.

If the presence of dark forests versus light-colored deserts changes the amount of sunlight reflected back into space, and if reflectivity is called albedo, then life directly influences the planet's energy balance through this effect.

If living organisms incorporate carbon into their bodies, and if some of that organic matter is buried in sediment before it can decay, then that carbon is removed from the active cycle; if this happens, the total atmospheric CO2 level decreases over time.

If oxygen was toxic to existing anaerobic life, it caused an extinction; if oxygen allowed for more energy-efficient metabolisms, it led to complex life; if it reacted with methane, it reduced the greenhouse effect and caused cooling.

If the Sun was 30% dimmer in the early solar system, and if the Earth did not freeze, then a strong greenhouse effect was needed; if methanogens were abundant and produced methane (a potent greenhouse gas), then they provided the necessary warming.

If large, multicellular animals require high amounts of energy to survive, and if aerobic respiration is the most efficient way to get that energy, then a high concentration of oxygen was a prerequisite for the evolution of complex animal life.

If mitochondria are the organelles responsible for aerobic respiration, and if aerobic respiration requires oxygen, then the rise of complex eukaryotic cells was dependent on the previous environmental shift toward an oxygen-rich atmosphere.

If roots break down minerals, they create soil; if vegetation stabilizes banks, rivers become meandering rather than braided; if weathering increases, nutrients flow to oceans; and if dead wood is buried, it forms coal.

If billions of tons of calcium carbonate (CaCO3) are deposited by marine life on the sea floor, and if this process is a major part of the long-term carbon cycle, then biological shell-building is a critical regulator of global climate and geological formations.

If early photosynthetic life or land-based weathering removed too much CO2 or methane from the atmosphere, then the greenhouse effect would weaken; if the heat trap failed, the Earth could have plunged into a global ice age.

If we are looking at how biological, geological, and chemical processes intersect in the rock record, then the scientific field is biogeochemistry.

If life moves an environment away from chemical equilibrium (like having O2 and CH4 together), and if life prefers certain isotopes over others, then these are the "bio-signatures" used to detect life elsewhere.

If the removal of CO2 from the atmosphere depends on the weathering of silicate rocks, and if plant roots and associated fungi accelerate this weathering, then life acts as a major "pump" that drives the Earth's long-term climate regulation.

If the current atmosphere, the composition of the oceans, and the types of minerals in the crust have all been significantly modified by biological activity over billions of years, then the modern Earth is a "bio-geological" system, not a purely geological one.