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The current view of science is that Earth is around 4.6 billion years old. The first four billion years of its development are known as the Precambrian period. For the first billion years or so, there was no life on Earth, and then the first single-celled life-forms, early bacteria and algae, began to emerge. It’s unknown where they came from or even if they originated on this planet at all, but this gradual development continued until suddenly (in relative geological terms), more complex forms of life began to emerge.

The early history of Earth covers such vast stretches of time that years, centuries and even millennia become virtually meaningless. The first four billion years of its development are known as the Precambrian period. For the first billion years or so, there was no life in Earth. Then the first single-celled life-forms, early bacteria and algae, began to emerge. We don’t know where they came from or even if they originated on this planet at all.

Mankind's obsession with felines is an enigma in and of itself. Unlike dogs, famously known as man's most excitable, trustworthy, and loyal friend, cats are oftentimes indifferent, guarded, and yet finicky little furry creatures that only yearn for attention and affection when one is neck-deep in work or otherwise preoccupied. And still, people adore them all the same.

The early history of our planet covers such vast stretches of time that years, centuries, and even millennia become virtually meaningless. Instead, paleontologists and scientists who study geochronology divide time into periods and eras. The current view of science is that planet Earth is around 4.6 billion years old. The first four billion years of its development are known as the Precambrian period.

Imagine a feline with the spirit of a lion, the sneakiness of a puma, the terrifying walk of a black bear, and the strong arms of a gorilla. This amazing creature was best known as the saber-toothed tiger, an animal so fearless, it could beat beasts even twice their size! After dinosaurs, few vanished animals are as famous as the woolly mammoths, or in 18th-century scientist George Cuvier’s words, "some kind of extinct elephant".

As the oft-repeated and invariably accurate pearl of wisdom goes, a dog truly is man's best friend. For a long time, people have almost universally loved dogs, and it seems to have been that way for at least tens of thousands of years. When affection is abundantly and consistently expressed, this pure, unspoken, wholesome love is one that is very much requited, and then some. This bond can be demonstrated by the mere existence of pet keepers who unironically refer to themselves as “dog parents,” not merely “dog owners”.

Scientists have long attempted to understand Earth’s past, and in service to that effort, they have divided the world’s history into eons, eras, periods, epochs, and ages. For example, the current eon is called the Phanerozoic Eon, which means “visible life”. This is the eon in which multicellular life has evolved and thrived. Before this, life was microscopic (single cells).

It is difficult to ignore the effortless cool of a saber-toothed tiger. The fanged feline was equipped with the savage strength of a lion, the lethal stealth of a puma, the intimidating gait of a black bear, and the strapping, muscular arms of a gorilla. Amazingly, however, those traits did not stand out as much as the long, dagger-like fangs that earned the Smilodon its famous nickname. The saber-toothed tiger, legend has it, was as ferocious as it was fearless, often tackling beasts twice its size.

At one point or another, just about everyone has heard of the dodo bird, which is almost universally described as a cuddly, whimsical creature renowned for its alleged stupidity. This prehistoric avian had been known for hundreds of years, before it was made popular around the world in Lewis Carroll’s 1865 classic Alice's Adventures in Wonderland.

Standing around 10 feet tall and weighing several tons, woolly mammoths seem like the stuff of legend, but ancient cave art indicated that unlike dinosaurs, woolly mammoths were contemporaries of early humans, with the last ones going extinct only about 4,000 years ago. All of that explains why people have long been fascinated by woolly mammoths and have even envisioned bringing them back to life via genetics sometime in the future.