What Was It Like When The First Humans Arose On Earth?
“Approximately 300,000 years ago, the first Homo sapiens — anatomically modern humans — arose alongside our other hominid relatives. It is unknown whether we descended directly from Homo erectus, heidelbergensis, or antecessor, although neanderthals, which came slightly later at 240,000 years ago, most certainly came from Homo heidelbergensis. Modern speech is thought to have arisen almost as soon as Homo sapiens did.
It took 13.8 billion years of cosmic history for the first human beings to arise, and we did so relatively recently: just 300,000 years ago. 99.998% of the time that passed since the Big Bang had no human beings at all; our entire species has only existed for the most recent 0.002% of the Universe. Yet, in that short time, we’ve managed to figure out the entire cosmic story that led to our existence. Fortunately, the story won’t end with us, as it’s still being written.”
For those of you who haven’t been following, this is now part 30 of my series on “what was it like when…” where I’ve been chronicling our natural history, from before the Big Bang up through the present day. Next week’s will be the final installment of that series, as we’ll arrive at the present!
This edition takes us from 65 million years ago to just 300,000 years ago: the development of modern humans. Come take a read; it’s the story of us all.
What Was It Like When Life’s Complexity Exploded?
“It is no doubt an oversimplification to state that horizontal gene transfer, the development of eukaryotes, multicellularity, and sexual reproduction are all it takes to go from primitive life to complex, differentiated life dominating a world. We know that this happened here on Earth, but we do not know what its likelihood was, or whether the billions of years it needed on Earth are typical or far more rapid than average.
What we do know is that life existed on Earth for nearly four billion years before the Cambrian explosion, which heralds the rise of complex animals. The story of early life on Earth is the story of most life on Earth, with only the last 550-600 million years showcasing the world as we’re familiar with it. After a 13.2 billion year cosmic journey, we were finally ready to enter the era of complex, differentiated, and possibly intelligent life.”
For the first few billion years of planet Earth, our world indeed had life occupying practically every niche we could imagine, but it was vastly different from the life we recognize today. Rather than complex, differentiated, multicellular organisms, all life in the early stages was single-celled and simple. Seemingly all at once, life’s complexity exploded some 550-600 million years ago during the Cambrian era. But this was no miraculous single event, but rather the culmination of many steps that worked together, in tandem, to make it all possible.
It took 13.2 billion years of cosmic evolution to give rise to the first megaflora and megafauna we find on Earth. Here were the critical steps that got us there.
What Was It Like When Oxygen Appeared And Almost Murdered All Life On Earth?
“This might be a simple biological scenario, but its results are nearly universal. In the presence of virtually no competitors or predators, and given practically unlimited resources, a living population will grow at an exponential rate. It will consume the available resources, produce whatever metabolism products it produces, and then reproduce in greater-than-replacement-level numbers.
The next generation will then consume more, produce more of its metabolites, and reproduce even greater numbers. So long as resources are freely available, this process will continue. Until, that it, the metabolic processes it has been undergoing build up to a critical level where it poisons its environment. If this sounds like what the yeast did — or what modern humans are doing with CO2 — you’ve put the pieces together correctly. Organisms, if left unchecked, will poison their habitat with the waste products of their own success.”
Approximately 2.5 billion years ago (but maybe more), a key development occurred in life on Earth: some unicellular creatures that were capable of photosynthesis began producing oxygen as an end-product of their metabolic processes. For hundreds of millions of years, these early cyanobacteria succeeded tremendously, but their success had a by-product: the oxygen poisoned the other organisms around them, as well as the environment as a whole. In short order, Earth was transformed into a giant snowball, leading to perhaps the greatest mass extinction in history: the Huronian Glaciation.
There are lessons to learn here, about ourselves, our environment, and how fragile our climate is. Come get the story of Snowball Earth today.