With your arms spread again to represent all time on earth, look at one hand with its line of life. The Cambrian [544 million years ago] begins in the wrist, and the Permian Extinction [250 million years ago] is at the outer end of the palm. All of the Cenozoic [the last 65 million years] is in the fingerprint, and in a single stroke with a medium-grained file you could eradicate human history.
He explains that the average lifespan of a mammalian species is about 2 million years. Depending on how you judge human evolutionary lineage, we are either just getting started as homo sapiens about 300,000 years ago or we are already in our senescence as homo erectus. In either case you are positing a time when human beings will no longer exist. You are positing a limit on the lifespan of the human species.
In doing so, you are inadvertently laying the groundwork for a different sort of relationship with the natural world than the one humans have had in the last 150 years or so, since the advent of fossil fuels. Modern humans often imagine themselves invincible, living as a species forever into the future, colonizing space, and perhaps even escaping the destruction of the Sun many billions of years hence. This kind of thinking--grounded in neither geology nor paleontology nor ecology I might add--has created the rather cavalier attitude demonstrated by modern leaders and their citizenry toward the daunting dangers of climate change, resource depletion and ecosystem collapse. If you think that as a species you are going to live forever, you don't need a Plan B.
But the humble geologist or paleontologist might take a different tack. Rather than assume clear sailing ahead, he or she might check the fossil record and pursue a more modest goal: extending our stay as humans on the planet a little longer than normal. Doing that would require careful attention to the tricks of species that have lived on Earth much longer than humans. Perhaps the most important lesson is that long-lived species don't destroy their own habitat. Sounds simple, doesn't it?
The point of my journey into the deep time of the geologist and paleontologist is not so much to pick up useful tips from long-lived species. Rather, it is to suggest that the way we think about the human future influences heavily what we do day to day in the here and now. The optimists believe we live outside the realm of nature, and we may pay for that optimism with an earlier than necessary demise as a species. On the other hand, those scientists who are in touch with the deep time of the past accept limits on the human journey. It is their way of thinking that provides a path back to a more sensible view of our relationship with the natural world.