Astro2110 – The Solar System

The formation of Earth and its current sustainability as they only known life-sustaining body in the universe have been caused by a number of extremely specific conditions which combine to make our planet the only one on which life is known to thrive. In this post, I will survey two of the specific conditions on Earth which allow life to thrive (tectonic activity and the greenhouse effect) and examine their historical causes through an astronomical lens. This survey of conditions is intentionally not exhaustive. Instead, this survey will give a deeper appreciation for some of the conditions that allow us to exist. We should take care to appreciate the extreme “luck” that allows us to exist here, in our seemingly lifeless universe, and thus realize the uniqueness of our home.

Tectonic activity is a fundamental component of Earth’s geology and it is essential for sustaining life on Earth. One extremely significant consequence of tectonic activity is the formation of volcanoes (and volcanic eruptions). Volcanic eruptions allow the Earth to release “geological stress” by creating an upwelling of magma through pressure that is then released on the lithosphere in an eruption. Although eruptions are very often harmful to life in the short-term, they mediate weather with reflective ash and enrich soils. Eruptions are often responsible for ecological succession, where existing forests are damaged or destroyed by volcanic eruptions, which enrich the soil in the medium to long-term by depositing ash and recycling nutrients into the ground. The emerging forests are more ecologically resilient (and biodiverse) compared to the forest that existed before the eruption. Volcanic activity is likely responsible for taking Earth out of its most recent “snowball” phase (approximately 600 mya), during which oceans were very widely covered by ice (and therefore not releasing substantial carbon dioxide into the atmosphere and sustaining a greenhouse effect). Gradually, outgassing from volcanoes is believed to have released sufficient carbon dioxide into the atmosphere to restabilize temperatures on Earth. Thereafter the biodiversity of life increased tremendously in the Cambrian Explosion, a central event that has preceded the wide diversity of life on Earth in relatively recent geological history.

The greenhouse effect has been essential for sustaining temperatures that are conducive to the continued existence of liquid water and the subsequent life that has existed on Earth. Greenhouse gases, which exist in relative abundance in Earth’s atmosphere (such as ozone, water vapor and carbon dioxide). Earth’s early atmosphere was rich in carbon dioxide, methane and water vapor, which absorbed and reemitted heat (which would have otherwise been lost into space) back onto the surface of the Earth. While this was happening, photosynthetic microorganisms were actively producing oxygen, which accumulated in the atmosphere over approximately one billion years. The proliferation of oxygen has given rise to nearly all existing life today, particularly by facilitating the presence of ozone (a reactive molecule with three oxygen atoms) in the stratosphere (part of the “upper” atmosphere. The reactive ozone “layer” absorbs solar ultraviolet light, which would otherwise reach the surface and significantly damage existing life on Earth. Relatively stable temperatures have proven to be essential for life’s resilience even in the most trying of times, and will remain essential for life’s continued existence on Earth.

Both the greenhouse effect and plate tectonics have proven absolutely essential for our incredible world, but they exist among other essential patterns (such as rotation and the magnetosphere) that work cohesively to sustain life on Earth. By understanding the uniqueness and importance of the processes which sustain our world, we only stand to gain more appreciation for the work we must do to maintain conditions that can sustain life for our generation and those to come.