50 million years ago, not long after an asteroid killed off the last of the dinosaurs, the earth in some ways looked similar to the earth we know today. But in many ways it was an entirely different and severely inhospitable place with soaring temperatures.
As the Gulf of Mexico recovered from an astroid hit, the rock under its ocean still a burning hot mess of hydrothermal vents, life on Earth was beginning to take new shape as mammals began their rise to one day gain dominance over the planet.
Lemurs and all sorts of ungulates, including ancestors of the hippo and tapir, roamed the planet. Alligators and fifty foot boas patrolled the rain forest while sharks infested the surrounding waters. It all sounds oddly familiar. But these rainforests weren't located near the equator. They were in the Arctic Circle. In present day Antarctica, ocean temperatures may have topped an astonishing 86 degrees Fahrenheit.
This was the climate of the late Paleocene and early Eocene epochs, when the U.K. may have looked more like the everglades or Germany like the Amazon. From 45 to 60 degrees latitude, it was nothing but hot, steamy wetlands. And what about the tropics, where you would expect to find boas, lemurs and tapirs today? They very well may have been massive dead zones, where temperatures rose above 120 degrees Fahrenheit and no form of life was able to find a foothold.
As for the atmosphere, it likely had a carbon dioxide level hovering around 1,000 ppm (parts per million), a number that our planet will be approaching by the end of the century. The good news is that none of this will happen again in the near future.
The last time the earth was at a carbon dioxide level of 400 ppm was around 3 million years ago, when ocean levels were 80 feet higher. We have once again reached 400 ppm, but we have a long way to go before ocean levels rise that much. Our climate is not yet at equilibrium for a planet with that level of carbon dioxide. It will clearly take much longer to match CO2 levels of 1,000 ppm.
But there is something else very troubling. The models which predict our future climates have largely failed to predict these ancient climates. In fact, in order to even come close to the hothouse earth of 50 million years ago, some models predict that we would need to inject 16 times the amount of CO2 currently in the atmosphere. So what's missing? The answer may be in methane - which there have been dire warnings about being released into the atmosphere as the earth warms.
One thing is for sure, as we keep releasing greenhouse gasses into the atmosphere we know that at some point we may be able to replicate the hothouse climate of 50 million years ago. It could even be within the next few centuries.
To read more check out the article at The Atlantic: https://www.theatlantic.com/science/archive/2018/08/earths-scorching-hot-history/566762/