Asteroids that slammed into Earth and the moon more than 4 billion years ago were vaporized into a mist of iron. A cloud of iron mist will have wrapped around the globe after any such collision, falling to Earth as metal rain. The iron mist thrown up from the high-velocity impacts of these asteroids traveled fast enough to escape the moon’s gravity but stayed gravitationally stuck on more massive Earth. This may help explain why the chemistry of the Earth and the moon differ.
2. Evidence of living organisms contemporary with the Hadean-eon formation of the Earth was recently discovered in Western Australian, dating nearly 1 billion years before the current fossil record. Scientists discovered 4.1 billion-year-old zircon samples (before even oceans appeared on earth) that had pockets of organic carbon. Some scientists even speculate that life itself is older than the earth, suggesting that life first appeared about 10 billion years ago, which is far older than the Earth’s projected age of 4.5 billion years.
3. Earth's oceans formed billions of years ago over vast periods of time. The water remained a gas until the Earth cooled below 212 degrees Fahrenheit. At this time, around 4.4 billion years ago, the water condensed into rain which filled the basins that are now our oceans.
4. Life most likely emerged on Earth almost instantaneously after becoming habitable. The first oceans formed 4.4 billion years ago, whereas current evidence supports the first life to have formed 4.28 billion years ago. Instantaneous of course means on a geological timescale here.
5. The earliest known life-forms on Earth are fossilized micro-organisms, found in hydrothermal vent holes in the seafloor. These were most probably chemosynthetic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material. Scientists have also recently found that hydrothermal vents at the bottom of the ocean are hot enough to emit enough light (mostly in the infrared spectrum) to support photosynthetic bacteria.
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The vast majority of the Earth's gold and other heavy metals are locked up in the earth's core. Evidence from tungsten isotope studies indicates that most gold in the crust is derived from gold in the mantle which resulted from a meteorite bombardment some 3.9 billion years ago.
7. Purple Earth hypothesis suggests that early life forms on Earth may have been able to generate metabolic energy from sunlight using a purple-pigmented molecule called retinal that possibly predates the evolution of chlorophyll and photosynthesis. As a consequence, early Earth’s landmass may have looked purple.
8. Recent studies have suggested that photosynthesis may have begun about 3.4 billion years ago. But before photosynthetic organisms developed, the earth might have not been a blue planet at all. The unoxidized iron in the ocean might have given it a dark green or even black color. Then as photosynthesis ramped up, it would have turned the oceans red as the iron oxidized and the earth became a blue planet as the dissolved iron oxide precipitated to the bottom.
9. As many as six supercontinents are thought to have formed and broken up prior to Pangaea. Roughly 400 million years pass between each repetition of the supercontinent cycle, which is currently causing the Pacific Ocean to shrink until yet another supercontinent will someday be formed. The oldest supercontinent on earth is Vaalbara which formed 2.7 to 3.6 billion years ago.
10. Around 2.5 billion years ago, the Oxygen Catastrophe occurred, where the first microbes producing oxygen using photosynthesis created so much free oxygen that it wiped out most organisms on the planet because they were used to living in minimal oxygenated conditions
Before the Great Oxygenation Event which saw a rise in oxygen levels around 2.4 billion years ago, the earth’s atmosphere is thought to have originally been methane-rich. This would have given the sky anywhere from a purple to an orange tint due to hydrocarbon haze.
12. There is a period during Earth’s evolution where activity stalled which scientists dubbed ‘the boring billion’. Beginning roughly 1.7 billion years ago, the Earth became a slimy, near-static world of algae and microbes.
13. Salts do enter and form in the ocean, but they also leave it. Ocean salinity has been stable for billions of years. The two major processes capable of removing significant amounts of salt from the ocean are the formation of evaporites (rocks that form when restricted, salty water evaporates) and the sequestration of brine as groundwater on the continents. It's actually been proposed that the early ocean was saltier than today (maybe up to twice as salty). Salt was removed from the oceans over geologic time as the Earth cooled and the continents grew, providing more space favorable for salt/evaporite deposition and the formation of saline groundwater. It's been argued that modern-day salinity wasn't reached until relatively recently, perhaps playing a role in the origin and radiation of animal life (known as the Cambrian Explosion).
14. Some scientists have proposed that earth froze completely about 650 million years ago. Proponents of the Snowball Earth hypothesis argue that it best explains a billion missing years in earth's rock layers. They argue that miles of ice eroded those rock layers and sent the sediment into the oceans where they were plunged back into the mantle to be recycled. There are also very few fossil layers before this period.
15. The Cambrian Explosion was a Biological Big Bang that happened between 500 and 250 million years ago. Life went from moving slowly on the seafloor without any predation to suddenly all the different ecologies that we find today. Some scientists believe that the evolution of vision triggered this evolutionary event.
One of the prevailing theories for the cause of the Ordovician–Silurian mass extinction is a gamma-ray burst that struck the planet 450 million years ago and killed almost all life on Earth. Researchers speculate that a gamma-ray burst originated from a hypernova within 6,000 light-years of Earth. A 10-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, exposing all life on earth to high levels of extreme ultraviolet radiation. Nearly 85% of marine species were wiped out.
17. 400 million years ago there were 22 hours in a day and more than 400 days in a year and 900 million years ago, there were 18 hours in a day. Also every 13,000 years or so, it's winter in July in the northern hemisphere (and vice versa for the southern) due to earth axial wobble.
18. Sharks are older than trees. Evidence for the existence of sharks dates back to 450 million years ago and modern trees only appeared around 350 million years ago. The first sharks were not only small but were at the bottom of the food chain. Sharks only became apex predators 100 million years ago and did not take over until just 15 million years ago. Before that, a succession of other large marine predators either ate them, gave them stiff competition, or both.
19. 358 million years ago insects got really big. Millipedes and centipedes were larger than humans, dragonflies grew big as eagles and beetles were the size of a large dog. The leading theory behind ancient bugs getting so big is that they benefited from a surplus of oxygen in Earth's atmosphere. Earth became abundant in oxygen because trees were new on the scene and they were able to grow because of lignin. But when these trees died there were no organisms to could break down lignin so trees kept putting oxygen in the atmosphere but didn’t “balance the books” by releasing CO2 when they died.
20. 300 million years ago, towards the end of the Carboniferous period, Earth saw oxygen levels as high as 35% (vs 21% today). Lightning was far more damaging back then. This period is associated with the formation of large deposits of charcoal, which have been linked to massive wildfires. Not only was the oxygen concentration at a record high, but there were also huge deposits of wood that could serve as fuel. Due to the absence of organisms to break down wood, during this time tens of millions of years’ worth of forests piled up, which became the coal we use today.
The earth is currently not at its historical warmest. In Antarctica, scientists recently found fossil fragments of 13 trees that are over 260 million years old, meaning that this forest was growing at the end of the Permian Period, before the first dinosaurs. At that time, Antarctica was still at the South Pole. Again 53 million years ago, Antarctica was so warm that palm trees thrived along its shores. During these global hothouse extremes, there were no polar ice caps. Due to the effects of melted glacial ice and ocean floor configurations, there were times when the sea level was up to 300 meters higher than it is now, creating massive interior seaways in most continental areas.
22. Around 234 million years ago, Earth's climate changed due to increased CO2 production possibly from increased volcanic activity caused by the separation of Pangea. This led to an increase of global temperatures, and humidity, which in turn meant more rainfall in this hot dry world and it kept raining for over 2 million years. So much rain caused complete extinction of organisms that were eventually replaced by the dinosaurs in the Jurassic Period. This wet period of the earth is known as the Carnian Pluvial Event.
23. It takes the Earth (and the Sun) 226 million years to orbit around the Milky Way Galaxy. This means that Earth has orbited around our galaxy about 20 times since the planet formed 4.5 billion years ago. This means the earth will turn 21 sometime in the next 100 million years or so and will die at roughly 53 by a house fire (swallowed by the sun).
24. Scientists have discovered the earth’s lost 8th continent. Plate tectonics separated this Greenland sized continent from North Africa more than 200 million years ago. Most of this continent was situated underwater and formed shallow, tropical seas in which sediment deposited, for example in large coral reefs. Without realizing it, vast numbers of tourists spend their holiday each year on this lost continent which is presently buried under Southern Europe and has been named Greater Adria.
25. Newly discovered fossils show that moths and butterflies have been on the planet for at least 200 million years whereas flowering plants came along around 130 million years ago. So butterflies survived without flowers for 70 million years.