The crumpled skin of the earth

Four billion years ago, at its formation, Earth was entirely uninhabitable – excessive amounts of carbon dioxide, unbearable temperatures and no solid ground to walk on. Earth’s crust has been observed since the first appearance of our remote ancestors, but even after decades of research and computer simulations, modern scientists are still trying to answer the fundamental question: How did Earth develop into a dynamic surface that sustains life? The formation of Earth's crust is a complex and fascinating story that spans billions of years and is the result of geological processes and events which are still not fully understood. The evolution of our planet has remained a subject of intense debate among scientists.

In recent years, scientists have made ground-breaking discoveries that have shed new light on the formation of the Earth's crust. The initial state of Earth was very hot – a fiery ball of lava being constantly bombarded by debris from the solar system’s formation. But eventually, after about half a billion years, the planet began to cool and solidify. Again and again this initial crust was ruptured by meteorite and asteroid impact, as well as by gravitational influences of the moon which then was much closer to earth than it is now, but gradually, things began to settle down and constructive forces dominated over destructive ones. Torrential rains followed the furnace-like conditions and oceans formed –before long, that is after another 100–200 million years or so, the first very primitive life forms appeared in the depth of the newly formed ocean that spanned the world.

One of the most significant events in the formation of the Earth's crust was the formation of the first landmasses, called cratons. They looked nothing like today’s continents, and they were swimming on an ocean of liquid rock – growing and shifting, drifting apart and colliding. In processes lasting hundreds of millions of years, the supercontinent of Gondwana formed, which combined the landmasses of Africa, South America, Australia, Antarctica, Arabia and India.

The formation of mountains are other significant events in the evolution of the Earth's crust. The crust consists of tectonic plates which float on top of the semi-liquid mantle. Mountains are created when tectonic plates collide, and one plate is pushed up and over the other. This process is called subduction, and it creates towering fold mountain ranges such as the Andes, the Himalayas and the Rockies. In the past, such tremendous geological events also happened in what became southern Africa, for instance the creation of the Damara Orogen of central Namibia some 550 million years ago. Then erosion took its toll and reduced these mountains to their present-day state – remnants of this particular range include the Otavi Mountains, Chuosberge, Rössing and the Naukluft.

The Earth's crust is also shaped by volcanic activity, which is often related to the mountain folding events. Volcanic eruptions can cause massive changes to Earth's surface, such as the creation of new land and the formation of new mountains. The release of gases and minerals into the atmosphere may change the climate for years or even decades (e.g. the Krakatau eruption on Java, Indonesia, in 1883).

Other mountains are formed by masses of molten rock rising through the Earth’s crust and cooling as they near the surface. Examples in Namibia are the Brandberg Massif with the country’s highest peak, as well as Spitzkoppe and Erongo, which consist of weather-resistant granitic rock that remained when erosion removed the surrounding softer sedimentary rock like schist.

All this goes to show that Earth’s crust is not just a static layer of rock, but a dynamic and constantly changing entity that has evolved and changed over billions of years. Most of these changes occur through incredibly slow processes, but over sufficiently long periods of time they create Earth's features and properties as we know them today. While some processes are constructive, like the slow deposition of massive layers of sediments on the ocean floors and the building of mountains, others are destructive. As soon as new features have formed, erosion attacks them with wind and rain, or temperature changes, which weakens the rock and eventually reduces it to rubble once more. A well-known erosional feature is the Vingerklip near Khorixas, a remnant of rock which weathering has shaped like an upraised thumb. Or the even more famous Finger of God (Mukorob) near Asab, which toppled over in 1988. Partly erosional and partly tectonic (the latter means shaped by forces at work in the Earth’s interior) is the Fish River Canyon. To a large part it was excavated over millions of years by the longest river in Namibia – hard to believe if one looks at the Fish River today, which for much of the year is but a trickle of water. This continuous process of birth and destruction is the geological cycle.

With its crumpled and textured surface, Earth’s crust is a living record of geological events. As we continue to explore it, we gain a deeper understanding of the history of our planet and the forces that continue to shape it.

Victoria N Nakafingo