Imagine sitting on your comfy couch, closing your eyes, and travelling back through time one billion years into the past. Upon opening your eyes, you'd probably find yourself gasping for air, lucky to survive five minutes before suffering an agonizing death, either by asphyxiation or drowning in a toxic ocean.
This is because the Earth, one billion years ago, was an extremely toxic place. The entire planet was practically uninhabitable due to the abundance of microbes and an atmosphere made out of harmful and poisonous gases illuminated by ultraviolet rays. Instead of pristine waters and unpolluted beaches, the ocean was a black and inky pool of sludge, and the shore was barren, dry and hostile.
Before the Neoproterozoic age, or roughly 1 billion to 500 million ago, life on the planet mainly had been entirely under the ocean. There were still no plant or animal life like we are familiar with today. Back then, the bottom of the Earth's deepest oceans were full of diverse and alien-like eukaryotic single-celled organisms.
As the planet gradually cooled and the sun, now more mature, began to warm the Earth, more complex creatures developed, including the choanoflagellates. This organism would be the precursor of all multicellular life today, including humans. Five of these groups became the ancestors of 21st century Protozoa, Slime molds, Animals, Plants & Algae and of course, Fungi.
The Earth's landmasses were also quite different one billion years ago. Instead of the familiar seven continents we have today, there was only one giant supercontinent called Rodinia. Take note that it was in no way, however, the first supercontinent on Earth. Rodinia was only one of a series of them, pushed together and torn apart by the massive forces of plate tectonic movements. It continued to reshape the planet's surface, forming a second supercontinent called Pangea, which lasted about 300 million years.
Rodinia, despite its size, was also inhospitable, and it was barren though the land was chockful of minerals. The sun was emitting damaging UV rays and the oxygen level, only at 2% (compared to our current 21%), which was still not enough to create an effective ozone layer. Two major glaciation periods (an extreme form of climate change) occurred as well.
One billion years ago, a slow, steady and silent revolution took place on our planet. Evolution was at hand, with simple microbial organisms slowly growing into more diverse complex lifeforms. Landmasses were pushed together and pulled apart, slowly forming terrains familiar to us today. The weather was erratic, with devastating climate change episodes and significant changes in the atmosphere.
However, it would also be the last time in the history of our planet that it would look so different from what we are familiar with now.