There were moments, in the past, when everything seemed lost, when the world was engulfed by darkness, when there was no chance of survival, when Earth seemed to have been invaded by Martians.
Those moments can be divided into two, tremendously cold moments and tremendously hot moments. Next, we will be able to refoculate ourselves in these two apocalyptic moments of the Earth that represent diametrically opposite points of mercury.
Very very cold
The cold is an enemy of life, except for some extremophilic organisms. In that sense, the iciest moments in Earth's history took place with the calls glaciations.
These phenomena are regular, appear from time to time, as in Game of Thrones. The reason is that the Earth wobbles like a spinning top, which changes the axis of the Earth every 41,000 years. In addition, every 100,000 and every 400,000 years, the elongation of the Earth's orbit varies. Both phenomena give rise to the so-called Milankovic cycles. The glaciations, then, have no greater secret.
However, glaciations became much bloodier about two million years due to two seemingly bland events that were propitiated by the movement of tectonic plates:
-The Himalayan mountain range increased its elevation.
-North and South America joined by Earth.
What does that have to do with the cold? The first point was the modification of the air of the whole of the planet's surface. The second point, to close the tropical channel that allowed the exchange of water between the Pacific and Atlantic oceans, thus enhancing a north-south flow. On Earth everything is connected in some way, and butterfly flutters cause tsunamis in the other part of the world.
Each time one of these glaciations arrived, our ancestors were about to become extinct. All in all, these glaciations were nothing compared to those that appeared in older times. Not in vain, these episodes are known as superglaciations (which is not very original) or Snowball Earth (seriously). Approximately 650 million years ago, they lasted millions of years, and were caused by algae, as he explains Marcus Chown in his book The universe in your pocket:
The causes are debated. But a probable explanation of the oldest of these episodes is that it was caused by blue-green algae that, suddenly, acquired evolutionarily the ability to divide water molecules and release oxygen through photosynthesis. That novelty occurred about 2.3 billion years ago. The oxygen emitted by those cyanobacteria destroyed methane (a greenhouse gas very abundant until then in the atmosphere) that kept the planet's surface warm.
The closest thing to such a cold in recent times was the small ice age that took place in Britain between the 17th and 18th centuries. The Thames froze, and fairs were held on the ice. The first one was held in 1309, and the last one, in 1814.
In the next installment of this article, we will enter the hottest moments on Earth.