Humans were adaptable beings. What would kill or wipe out other races due to a lack of intelligence or options, humans often could squeeze out enough as a species to endure even in very harsh conditions.
Extreme temperatures, city destroying natural events, or just plain bad choices could all lead to cataclysmic events but so long as enough humans acted in concert or independently, the race could recover.
History did not always record those moments as many were too busy surviving, but some traces endured. They became myths and legends to later generations and just mysteries or excuses to later generations.
The sudden collapse of all advanced civilizations at roughly the same time had been the most widely accepted first recorded event for Earth but how many had simply been unable to be recorded because everything had been on the brink of the end?
