New Delhi: With world leaders and climate activists set to converge in Dubai in the United Arab Emirates (UAE) on November 30 for COP28 (28th Conference of the Parties of the United Nations Framework Convention on Climate Change) to discuss climate change mitigation, it is important look at how the earth’s crust plays a crucial role for sustainability of life.
The earth’s crust plays a crucial role in shaping surface habitability through processes like outgassing and the recycling of volatiles. It is the outermost shell of the earth, and it is divided into several tectonic plates that float on the semi-fluid asthenosphere beneath them. The earth’s crust influences habitability in two key ways – outgassing and recycling of volatiles.
Volcanic activity is a part of the outgassing phenomenon. The earth’s crust is dynamic, with tectonic plates constantly moving and interacting. This movement leads to volcanic activity, where molten rock or magma from the earth’s interior can reach the surface through volcanic eruptions. During these eruptions, gases and volatiles, such as water vapour, carbon dioxide, nitrogen, and sulphur compounds, are released into the atmosphere. This outgassing is critical for the development and maintenance of the earth's atmosphere.
“The earth has a unique atmosphere formed mainly due to the degassing or outgassing during the initial hot conditions from the volcanoes,” B Sreenivas, Senior Principal Scientist in the National Geophysical Research Institute, explained to ETV Bharat. “These volatiles are mainly hydrogen sulphide, methane, and carbon dioxide. The noble or inert gases such as helium, argon, neon, xenon and krypton also accumulated in the atmosphere in trace amounts. The volatile accumulation and recycling played a crucial role in shaping the surface of the planet.”
The outgassing of volatiles contributes to the composition of the earth's atmosphere. For example, water vapour released from volcanic activity can condense and form clouds, leading to precipitation and the development of liquid water on the surface - a key ingredient for life.
The earth’s crust is also involved in the process of plate tectonics. Tectonic plates move, collide, and subduct beneath each other. Subduction zones are regions where one tectonic plate is forced beneath another into the earth’s mantle. This process plays a crucial role in the recycling of volatiles.
“Although the manifestations of volatile recycling appear at the surface of the earth prominently, the reasons behind their changes can happen in the deep interior of the Earth,” Sreenivas said. “The plumes, which act as
conduits of heat supply from the outer core resulting from large catastrophic flood basalt volcanic events such as the Deccan volcanic province, bring in huge volatiles to the surface. Some of these large catastrophic events led to the mass extinctions like the extinction of dinosaurs.”
He said that the Toba volcanic eruption around 70,000 years back have impacted the migrations of early humans suggesting that such catastrophic large volcanic events have affected life in many ways.
The Toba eruption was a supervolcano eruption that occurred during the Late Pleistocene at the site of present-day Lake Toba in Sumatra, Indonesia. It is one of the largest known explosive eruptions in earth’s history. The Toba catastrophe theory holds that this event caused a severe global volcanic winter of six to ten years and contributed to a 1,000-year-long cooling episode, leading to a genetic bottleneck in humans. “The recycling of volatiles has therefore played an important role in shaping the habitable planet,” Sreenivas said.
The subduction zones, as mentioned above, are also particularly important for the carbon cycle. When organic material and carbonate rocks are buried in subduction zones, they release carbon dioxide upon reaching high temperatures and pressures in the earth’s mantle. This carbon dioxide is eventually returned to the atmosphere through volcanic activity.
Water is also recycled through subduction zones. Oceanic plates, rich in water-containing minerals, are subducted beneath continental plates or other oceanic plates. This water is released during subduction and can contribute to the formation of volcanic arcs and the maintenance of the water cycle.
Water cycling is essential for nutrient cycling. Rocks and minerals on the earth’s crust weather over time, releasing essential nutrients into the soil. This weathering process, facilitated by physical, chemical, and biological mechanisms, provides the necessary elements for plant growth. Plants, in turn, form the basis of terrestrial food chains, supporting higher forms of life.
While the earth’s crust does not directly create life, it establishes the environmental conditions and processes that are conducive to the emergence, sustenance, and evolution of life. The dynamic interactions between the earth’s crust, atmosphere, oceans, and living organisms have created a complex and interconnected system that has supported life for billions of years.
