About 50 million years after Earth formed, it was struck by a large, Mars-sized object named Theia. The aftermath of the collision superheated the Earth and kicked up an enormous amount of debris, a large fraction of which wound up forming the Moon. The remainder either escaped the Earth-Moon system or fell back onto one of the two bodies. While the Moon’s far side cooled more rapidly, the near side, due to its facing the hot Earth, remained hotter for much longer. This is one of the leading scenarios for explaining the differences between the Moon’s Earth-facing and Earth-opposing hemispheres. (Credit: Mark Garlick / Science Photo Library / Alamy)
Our cosmic home, planet Earth, has been through a lot over the past 4.5 billion years. Here are some of its most spectacular changes.
Our Solar System formed some ~4.6 billion years ago.
Although we now believe we understand how the Sun and our Solar System formed, this early view of our past, protoplanetary stage is an illustration only. Today, only eight planets, with most possessing moons, as well as small rocky, metallic, and icy bodies distributed across various belts and clouds. (Credit: JHUAPL/SwRI)
Eventually, eight planets emerged, with a giant impact creating Earth’s Moon.
When two large bodies collide, as they very likely did between proto-Earth and a hypothesized Mars-sized world known as Theia in the early Solar System, they’ll generally merge to form one more massive body as a result, but the debris kicked up from the collision can coalesce into one or more large moons. This was likely the case not only for Earth, but for Mars and Pluto and their lunar systems as well. (Credit: NASA/JPL-Caltech)
Here are 7 ways the Earth has subsequently changed.
Early on, even small-mass planets like Earth had a large hydrogen and helium envelope. Due to their low gravity, solar wind and radiation swiftly stripped that primitive atmosphere away. (Credit: NASA’s Scientific Visualization Studio and the MAVEN Science Team)
1.) Atmospheric composition. Early on, hydrogen and helium dominated.
Volcanic activity present on Earth, including from the earliest times, released large quantities of solid and gaseous material into our atmosphere, including nitrogen, carbon dioxide, and water, which transformed our young hydrogen/helium atmosphere into a nitrogen/CO2/H2O rich atmosphere, which would further be transformed by biological processes. (Credit: C. Werner et al., in Deep Carbon: Past and Present, Cambridge University Press, 2019)
Volcanic and biological activities were transformative.
After losing its hydrogen and helium envelope, Earth’s early, volatile-rich atmosphere became strongly influenced by geological and biological processes, eventually creating the atmosphere we have today. (Credit: Kate M., Socratic, 2016)
Today, our nitrogen/oxygen atmosphere has hints of water, argon, and carbon dioxide.
While modern Earth has had plate tectonic activity for at least the past 2 billion and potentially as much as 4.3 billion years or more, the earliest phases of our planet’s history are expected to have lacked plate tectonics, as it only developed once water arrived and enough differentiation had taken place. (Credit: SciTechDaily/Ehime University)
2.) Plate tectonics. Early Earth was lava-rich, possessing poorly-differentiated internal layers.
These tiny zircon crystals, which are only as thick as a human hair, are over 4 billion years old and holds an enormous amount of chemical information about early Earth. The silicon, oxygen, and trace element and isotope contents in these zircons and their parental magmas suggest that plate tectonics existed on Earth more than 4 billion years ago. (Credit: Smithsonian Institution)
With severe energy gradients, a mobile lithosphere, and liquid water, plate tectonics are undeniable today.
Tidal rhythmites, such as the Touchet formation shown here, can allow us to determine what the rate of Earth’s rotation was in the past. During the emergence of the dinosaurs, our day was closer to 23 hours long, not 24. Back billions of years ago, shortly after the formation of the Moon, a day was closer to a mere 6-to-8 hours, rather than 24. (Credit: Williamborg/Wikimedia Commons)
