How did the Earth form?
Around 4.54 billion years ago, our solar system began as a giant cloud of gas and dust called a Solar Nebula which grew by the amalgamation of clumps of cosmic dust called planetesimals.
Under the force of gravity, the slowly rotating Solar Nebula collapsed and the contracting rotating cloud flattened to form a spinning disk. Within this disk, particles began to collide and stick together, forming larger bodies (planetesimals) which eventually coalesced into protoplanets.
At the centre of this disk, the largest concentration of matter became so hot and dense that nuclear fusion ignited, forming the Sun, and one of these protoplanets grew large enough to become Earth.
This process involved numerous collisions with other planetesimals, which contributed to Earth’s growth and generated a lot of heat. This heat caused the planet to partially melt, allowing denser materials to sink to the centre and form the core, while lighter materials formed the mantle and crust.
How did continents form?
Earth’s growth process was so violent that early Earth had a molten magma surface which started to harden and began to form a crust around 4 billion years ago. If water was present on Earth at this stage it would have occurred as vapour.
At the time, the Earth’s atmosphere consisted mostly of carbon dioxide and the atmospheric pressure was probably much higher than it is today. Although the Sun was cooler, the greenhouse effect would have resulted in very high surface temperatures.
During the Late Heavy Bombardment 3.8 billion years ago, an elevated frequency of collisions with asteroids is believed to have brought water to Earth and it is likely oceans have been a permanent feature ever since, and as the Earth cooled further, rain also began to fall.
This newly formed crust, more homogenous than the present crust, was initially unstable and frequently recycled through volcanic activity and impacts, and it is probable there were initially only a few islands formed by the peaks of large volcanoes.
Over time, Earth’s crust began to break up and reassemble. The first supercontinent, Rodinia, formed around 1.1 billion years ago. Supercontinents formed when most of Earth’s landmasses come together. Rodinia eventually broke apart, leading to the formation of new oceans and landmasses.
Around 335 million years ago, the supercontinent Pangaea formed, bringing most of Earth’s landmasses together. This arrangement persisted until about 175 million years ago, when Pangaea began to break apart into smaller continents.
The breakup of Pangaea led to the formation of the Atlantic Ocean and the separation of the landmasses into the continents we recognise today. For example, around 180 million years ago, Laurasia and Gondwana were the major landmasses, which eventually drifted into the continents we see today—North America, South America, Africa, Eurasia, Antarctica, and Australia. They are crucial in understanding the geological history of the Earth and the evolution of life as their breakup led to significant changes in climate and sea levels.
Nowadays, the movement of tectonic plates continues to shape the continents. Plates move due to convection currents in the mantle, causing continents to drift, collide, and slide past each other. This process is ongoing, leading to the formation of mountains, earthquakes, and other geological features.
The dynamic nature of Earth’s geology means that the positions of continents will continue to change over geological time scales.
References/Sources
www.calacademy.org
www.en.wikipedia.org
How on Earth? Terrence McCarthy (2009)
www.maropeng.co.za
www.nationalgeographic.org
www.sciencedaily.com
www.space.com
www.weforum.org