1Ocean Salinity
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).
2Snowball Earth
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.
3Biological Big Bang
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.
4Mass Extinction
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.
5Length of a Day
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.
6Sharks
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.
7Large Bugs
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.
Latest FactRepublic Video:
15 Most Controversial & Costly Blunders in History
8Charcoal
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.
9Warm Antarctica
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.
10Carnian Pluvial Event
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.
