The Dynamic History of Earth's Tectonic Plates Unveiled
Written on
Chapter 1: Introduction to Earth's Tectonics
The Earth's surface resembles a moving jigsaw puzzle, shaping the world we inhabit. Welcome to the 18th installment of the Earth’s history series.
The Earth's crust is remarkably thin, averaging just 15 to 20 kilometers in thickness, and exhibits brittleness akin to the hard shell of a crème brûlée. Beneath this fragile crust lies the mantle, a layer of molten rock that extends approximately 2,900 kilometers deep and is in constant motion.
Similar to the custard in a crème brûlée, the mantle is neither fully solid nor liquid; it possesses a viscous quality and is driven by powerful currents. Hot magma rises from the Earth's core to the top of the mantle, cools, and then descends, creating slow-moving convection currents that take about 500 million years to complete a full cycle. This process is enough to fracture the Earth’s crust, similar to how a teaspoon breaks the dessert's surface.
Section 1.1: Understanding Tectonic Plates
These fractured pieces of crust, known as tectonic plates, are studied under the field of plate tectonics (derived from the Greek word for 'building'). Technically, it is not just the crust that constitutes a plate; the upper layer of the mantle is also involved, collectively referred to as the lithosphere (Greek for 'rocky'). Beneath this lies the asthenosphere ('without strength'), the molten region of the mantle.
One could liken these plates to massive icebergs floating on a turbulent sea of magma. Some form of tectonic activity likely existed in Earth's formative years, but many geologists believe that significant processes began approximately 3.0 billion years ago.
Subsection 1.1.1: Earth's Major and Minor Plates
Today, there are seven major tectonic plates, each exceeding 43 million square kilometers in area. For context, the entire Asian continent covers about 44.5 million square kilometers, while the United States spans just 10 million square kilometers. The Pacific Plate, the largest at 103 million square kilometers, consists entirely of oceanic crust. Additionally, there are 15 minor plates ranging from 1.0 to 16.7 million square kilometers and over 50 microplates, including the small Juan de Fuca plate, which is roughly the size of the United Kingdom.
All these plates are in motion. Their interactions can lead to various geological phenomena: they may collide, forming mountain ranges like the Himalayas; they can pull apart, resulting in rift valleys such as those in East Africa; or they may slide past each other, as seen with California's San Andreas Fault.
When plates collide, one can be forced beneath another in a process known as subduction. As the lower plate descends into the mantle, it creates weaknesses in the crust, allowing magma to rise and giving birth to volcanoes. Beginning around 3.0 billion years ago, these tectonic forces started shaping the continents.
The first video titled "The evolution of Earth's tectonic plates over the past billion years" provides a visual representation of the dynamic changes that have occurred in Earth's tectonic framework over extensive time periods.
Section 1.2: Formation of Continents and Supercontinents
Over the course of the next 500 million years, 80% of the current continental crust was established. As the plates shifted over eons, they occasionally converged to form colossal landmasses known as supercontinents. We will explore some of these supercontinents as our narrative unfolds. The next anticipated supercontinent, Pangea Ultima, is projected to emerge in 250 million years.
The second video titled "Plate tectonic evolution from 1 Billion years ago to the present" delves into the historical transformations of Earth's plates, illustrating their impact on the planet's geography.
Chapter 2: Conclusion and Future Insights
This article is the 18th part of a comprehensive series detailing Earth's history, with each article focusing on a 100-million-year interval. For further reading, check out Part 17: THIRD or Part 19: TIME. If you wish to explore all the articles, please follow me.