When I was in 7th grade, we were taught that the earth was 4,500,000,000 years old. That was 31 years ago, making the earth 4,500,000,031 years old now. Time flies, huh? It seems like only yesterday when the earth was a mere 4,500,000,030 years old.
I make the above statement not to be funny, but to illustrate a point about large numbers, particularly how people generally tend not to be aware of how large numbers used in everyday conversation can really get. What does it mean that the earth is 4.5 billion years old? The oldest trees on this planet are the slightest fraction of that age. The age of the average human is a slight fraction of that. It's not surprising that comprehension of just how long 4.5 billion years is comes with some difficulty.
Allow me to try to illustrate just how large 4.5 billion is. 4.5 billion nanoseconds ago, you started reading this paragraph. 4.5 billion microseconds ago, photons in the light now reaching the earth from Jupiter were still miles below the sun's corona. 4.5 billion milliseconds ago, the planet Mercury was on the opposite side of the sun from where it is now. 4.5 billion seconds ago, Abraham Lincoln was still president. 4.5 billion minutes ago, farming was invented. 4.5 billion hours ago, Hawaii was formed by volcanic accretion, and early human ancestors had just learned to use charcoal to maintain fires, but probably didn't know yet how to start a fire. 4.5 billion days ago, early hominids had emerged, but did not yet walk upright. 4.5 billion weeks ago, sharks evolved, and 4.5 billion months ago, the Appalachian mountains were formed from the collision of the North American, African and European tectonic plates.
4.5 billion people make up 75% of the world's population.
A stack of 4.5 billion standard sheets of typing paper would be 279 kilometers tall, 31 times the height of Mount Everest's highest peak, and could easily reach completely across the English Channel at its widest point.
A stack of 4.5 billion one dollar bills would balance the US federal budget for nearly 3 days. A stack of 4.5 billion thousand dollar bills would eliminate over half of the US national debt.
Starting to get the picture yet?