Dog-Sized Scorpions: 6 Ways The Earth Was A Sci-Fi Nightmare

Back in 1859 in Canada, scientists started digging up the fossils of what they believed were ancient tree trunks, but it wasn't until 2007 that they finally confirmed the "tree" was a fungus. The organism, called Prototaxites, towered up to 24 feet tall and made a landscape that looked more like a Super Mario Bros. level than modern Earth.

And Prototaxites wasn't just confined to Canada. Fossil hunters have dug up the titanic shrooms all over the world, suggesting that it was probably the biggest life-form on land at a time when animal life was nothing but microbes and worms.

After plants learned how to stand up for themselves and stop getting pushed around by glorified athlete's foot, they started evolving trunks and hogging the resources Prototaxites needed to grow, so plants won the race and fungi were reduced to living off their rotting garbage.

During that age, oxygen levels in the atmosphere were up to 15 percent higher than they are today, thanks to a sudden explosive abundance of plant life. And it had an incredible impact on the kinds of animals that were able to flourish.

Insects today are limited in size only by the amount of oxygen they're exposed to. Our 20 to 21 percent oxygen level means that we climb onto a table if we see a cockroach any bigger than 1.5 inches. In the Carboniferous, you would have had to contend with scorpions the size of dogs, caterpillars you could mistake for anacondas, and dragonflies that could fight an albatross.

Combined with the fact that predators such as birds and reptiles were millions of years away from evolving, environmental conditions meant bugs could pretty much just grow until they reached B-movie proportions. But there was another side effect of such a high-oxygen environment -- the world was basically on fire all of the time.

Because fire is basically just what happens when you add oxygen and heat, it didn't take much to start a fire in the Carboniferous period. As a result, wildfires swept constantly across the globe, and it's speculated that smoke would have made the sky a permanent hazy brown. Picture it: Just a bunch of giant, flaming insects hurtling at you out of a blinding fog. Resident Evil was apparently historically accurate.

The reason that the land on Earth looks green from above is because of our plants, which are only green because of their chlorophyll. But plants didn't always harness chlorophyll -- back in the earliest stages of life, they used a different chemical called retinal, which is purple.

Scientists believe that, for some time, purple-colored organisms may have been so abundant on Earth that the whole place looked like Prince's home world.

Come on, you know he doesn't come from here.

It's sci-fi shorthand: If you want to quickly show that your hero ain't in Kansas anymore, just have him or her look to the sky and see two moons. It's one of the most alien things we can imagine. Compare that to Earth's moon, most commonly known as "the" moon (because we're #1!), which only has two sides: There's the side we see, the light side, and the side we don't -- the dark side.

The dark side has a much thicker crust and a more varied surface. If the moon hits your eye like a big pizza pie, well, the front side would be Brooklyn-style, and the rear is straight-up Chicago deep dish.

Scientists have wondered for a long time how the two halves could be so geologically different, and one theory suggests that, at some point in the distant past, the Earth actually had two moons, for a period of around 80 million years, before they got caught in each other's gravity and crashed together -- presumably while drunk.

These huge impacts created enough heat to vaporize metal, such as iron, gold, and platinum, which would have ascended into the atmosphere as a kind of metal vapor. And since what goes up has to come down, the early Earth would have experienced metal rain.

Still, early life shrugged off this calamity as just another every day thing. You wake up, you eat breakfast, you lounge about for a while, you bunker down for a global extinction-level event, you have dinner, you go to bed. It kind of puts human problems in a whole new perspective.

You might wonder, "Why are scientists spending so much money looking for life on Mars, when they could have given us sex robots, hoverboards, or sex robots on hoverboards by now?" One of the reasons is that, from all we know about life, it seems much more likely that it originated on Mars than here.

Billions of years ago, the environment on Mars was actually more hospitable than Earth. Life required a large amount of oxygen to form, but oxygen was relatively scarce here. It was plentiful on Mars. On top of that, life required the elements molybdenum and boron, of which there was also a whole heap on Mars, but not so much on Earth.

So, some scientists think that life first spawned on Mars, in a distant age before it became such an inhospitable wasteland, and came to Earth when some really hardy microorganisms hitchhiked on meteors that broke off the Martian surface.

Technically, we might all be invaders from Mars.

Micah Kolding can be found on an Internet-based site known as "Twitter," where he is known as @MicahKolding.

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Also be sure to check out 5 Insane Theories About Why We Haven't Discovered Alien Life and 5 UFO Sightings That Even Non-Crazy People Find Creepy.