Today I learned it rained all over our planet once for a million years or two. This was 233 or 234 million years during the Triassic period. The scientific name for this event is the Carnian Pluvian Episode. That was amazing for me to learn about, and what happened just before and after intrigued me even more.
Now before the rains came it was too darn hot. Volcanic eruptions had filled the air with so much carbon dioxide that the whole world was a desert, even the ocean was hot. The continents we have today hadn't developed yet, that's later in the Jurassic period. At this point the Earth was still one land mass of Pangea that was scorching, dry and flat, and with everything locked together rain clouds couldn't go far beyond the coastline so it stayed broiling, and there were no mountain ranges to break some of that up.
The reason it started raining was because there was enormous volcanic activity in what would be British Columbia and Alaska today, called the Wrangellian eruptions, which I also learned about today. This went on for 5 million years, producing such thick layers of lava that it raised the temperature even higher, over time the warming temperatures sped up the water cycle, forcing the surface water to evaporate into the atmosphere. So it became humid in short.
Now certain kinds of animals had adapted to live in this once arid place. However, when this endless rain came it threw everything into chaos for these species, and many of the early reptile and ancient cousins to mammals died off, clearing the path for dinosaurs to rise and become the dominant lifeform on the planet. Before this time dinosaurs existed, but they were not at the top of the food chain, the top predators were crurotarsins like Ornithosuchis, which looked like a crocodile with long legs to run on like a person.
In rock datings before the start of CPE dinosaurs made up just about 5% of the fossils of terrestrial cerebrates, but at the end they make up 90% of those fossils.
The rains fostered an environment where large coniferious plants started growing like bennettitales, and that would have altered the food supply, and may have been the key to why dinosaurs endured when many other creatures perished. Some of the lifeforms that had previously outnumbered dinosaurs were Rhyncosaurs, plump reptiles that were kinda cute. They ate plants, had big cheeks and little bird like beaks. They were stocky, but not tall, and crawled around on the flat desert-like environment and feasted on low-growing plants, but in a wet forest landscape, there were now these trees with high leaves and fruit that the poor things couldn't stand up on their stubby hind legs to reach and eat like dinosaurs could. Another herbivore that went extinct was dicynodonts, which looked to me a little like a rhino, and didn't have teeth. They were whimsical-looking, but having no teeth made it hard to digest the fiberous new plant material like woody trees. It was used to living on soft, small plants like ferns, that were now disappearing before their eyes as the landscape changed. Meanwhile dinosaurs had teeth and could chew bark, and some also could eat little rocks that may have helped them to grind up and digest the food material. Dicynodonts couldn't survive on that sadly. This would have also doomed the carnivorous species like crurotarsins because the dyconodonts and rhyncosaurs would have been their prey, so they too wouldn't be able to sustain their population either.
I have heard how dinosaurs became extinct, but I don't usually hear the story of how dinosaurs began to thrive. So interesting content from PBS.