Earth’s continents are predominantly shaped by the processes of continental drift and plate tectonics. Recently, a new study suggests that massive meteorite impacts, prevalent during the first billion years of our planet’s existence, significantly contributed to the formation of continents. This reality underscores the need for understanding continental formation, which is crucial, given most of Earth’s biomass and humans live on these landmasses.
Highlights of the Study
The research postulates that meteorite impacts generated substantial energy to form oceanic plates, which later evolved into continents. The theory has been in existence for decades, with little solid evidence supporting it until now. Currently, the most commonly accepted theory attributes continent formation to the movement of tectonic plates.
Evidence for the meteorite impact theory was provided by zircon crystals found in rocks from the Pilbara Craton in Western Australia – an ancient crust formed over three billion years ago. Zircons act as tiny time capsules, recording periods of geologic activity. Variations in isotopes of oxygen within these crystals were used to estimate past conditions, with older grains possessing lighter oxygen-16 and younger ones containing heavier oxygen-18.
Understanding Cratons
Cratons are old and stable parts of the continental lithosphere, comprising Earth’s two topmost layers – the crust and the uppermost mantle. Understanding their formation and evolution is vital, particularly because they are key reserves of metals like lithium, tin, and nickel.
Theories of Continent Formation
The two widely recognized theories related to continent formation are the plate tectonics theory and the continental drift theory.
Plate Tectonics Theory
Proposed between the 1950s and 1970s, the plate tectonics theory suggested that Earth’s outer shell is divided into large slabs of solid rock – known as “plates” – that glide over Earth’s mantle. This theory, an update to Alfred Wegener’s 1912 continental drift theory, explains how continents move around the planet.
Earth’s lithosphere, including the crust and uppermost mantle, is divided into seven major and several minor plates. These plates move around, facilitated by the lubrication provided by the asthenosphere – a viscous layer rendered malleable by heat deep within the Earth. The movement of these tectonic plates leads to three types of boundaries: convergent, where plates move into each other; divergent, where plates move apart; and transform, where plates move sideways in relation to each other.
Continental Drift Theory
The continental drift theory, first proposed by Alfred Wegener in 1912, deals with the distribution of oceans and continents. According to this theory, all continents were once part of a single mass – Pangea – surrounded by a mega ocean, Panthalassa. About 200 million years ago, Pangea split into Laurasia and Gondwanaland, which further broke down into the existing continents.
Evidence supporting the continental drift theory includes complementary shapes of different continents, like South America and Africa or India and Madagascar. Further support comes from similar fossils, geographical features, and mineral resources found across different continents.
Overall, understanding these theories forms a vital part of the study of Earth’s evolution and the shaping of its continents. Despite advancements and new findings, a full understanding of these processes continues to be explored and debated among scientists today.
