Author : Benjamin Hayworth
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (133 download)
Book Synopsis Atmosphere and Climate Evolution on Earth and Earth-like Planets by : Benjamin Hayworth
Download or read book Atmosphere and Climate Evolution on Earth and Earth-like Planets written by Benjamin Hayworth and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Long-term atmospheric and climate evolution on terrestrial planets is primarily controlled by the silicate weathering feedback and evolution of the host-star. The former acts to regulate the climate of rocky planets by controlling the concentration of greenhouse gases in the atmosphere - shaping the habitability of said planet. In this dissertation, In Chapter 2, I explore how the silicate-weathering and ice-albedo feedbacks control the climate of early Mars when sufficient amounts of atmospheric H2 are present. This study can help us constrain the possible martian environments that allowed surface liquid water in its distant past. Explaining the evidence for surface liquid water on early Mars has been a challenge for climate modelers, as the sun was ~30% less luminous during the late-Noachian. I propose that the additional greenhouse forcing of CO2-H2 collision-induced absorption is capable of bringing the surface temperature above freezing and can put early Mars into a limit-cycling regime. Limit cycles occur when insolation is low and CO2 outgassing rates are unable to balance with the rapid drawdown of CO2 during warm weathering periods. Planets in this regime will alternate between global glaciation and transient warm climate phases. This mechanism is capable of explaining the geomorphological evidence for transient warm periods in the martian record. Previous work has shown that collision-induced absorption of CO2-H2 was capable of deglaciating early Mars, but only with high H2 outgassing rates (greater than ~600 Tmol/yr) and at high surface pressures (between 3 to 4 bars). I use new theoretically derived collision-induced absorption coefficients for CO2-H2 to reevaluate the climate limit cycling hypothesis for early Mars. The long-term habitability of a planet is often assumed to be controlled by its ability to cycle carbon between the solid planetary interior and atmosphere. This process allows the planet to respond to external forcings (i.e. changes in insolation, changes in volcanic outgassing rates, etc.) and regulate its surface temperature through negative feedbacks on atmospheric CO2 involved in silicate weathering. In Chapter 3, I explore how the different, non-linear dependencies on pCO2 between continental weathering and seafloor weathering rates can control how a habitable planet responds to external forcings. The evolution of a planet's host-star may not only impact its habitability, but its prebiotic environment. In Chapter 4, I explore what impact an active young Sun may have had on the young Earth's prebiotic environment at the dawn of life. Earth's Hadean atmosphere is thought to have been dominated by N2 and CO2 except in the aftermath of large impacts, when CO and CH4 may have become abundant. Here, I investigate the effect of high fluences of solar energetic particles (SEPs) from the more rapidly rotating, magnetically active young Sun. These particles would have penetrated deeply into Earth's atmosphere, ionizing and dissociating ambient gases as they did so. If the level of solar activity was very high, as it would have been if the Sun began its life as a rapid rotator, rapid dissociation of CO2 would have created an atmosphere rich in CO and O2. Such an atmosphere would have been too oxidized to be conducive to the origin of life in a surface environment. As the solar rotation rate slowed, the SEP fluence would have dropped off, causing O2 to disappear but allowing CO to remain abundant. Thermodynamic free energy from the 'water-gas shift' reaction, CO + H2O -> CO2 + H2, could have exceeded 50-60 kJ/mol -- more than enough to power nucleotide polymerization or ATP synthesis. Hence, charged particle bombardment could have played an important role in the origin of life. These same types of processes may operate on Earth-like planets orbiting other G-type stars, most of which are more magnetically active than the Sun.
