I want to offer you a key to understanding the scientific theory of EVOLUTION. The key to really understanding evolution is opening our minds to the concept of geologic time.
Through most of our human history, we have only had to deal with measures of time that were important to our survival: the day, the season, the span of a lifetime. Anything beyond the years we might live was either the distant past, or the unknowable future.
Early attempts to determine the true age of the earth and the length of human history used the Bible. By assigning a certain number of years to each human generation described in the genealogies of the Old Testament, early scholars arrived at an estimate of some six thousand years from the time of earth’s creation to the time in which these estimates were made. (Six thousand years may be a long time, but it is a length of time we could grasp).
But with the rise of science and the ever-growing number of discoveries in geology, genetics, astronomy and biology, our modern brains are suddenly confronted with concepts and measurements that can literally make our heads hurt. And while we struggle to make sense of atoms and cells and viruses that are within our bodies, but which we cannot see with our own unaided eyes, we are also overwhelmed by measurements of time that have moved the age of the earth back into the darkness of history far beyond six thousand years.
HOW OLD IS THE EARTH?
We now know (from the geologic evidence) that the earth began to form some 4.5 billion years ago, or 4, 500 million years.
Thousands of hundreds of millions of years. To minds that live by minutes, days and months (that might in one lifetime add up to a hundred) we might as well call such millions of years “eternity” or “infinity”.
In fact, we do call them just that. Often we invoke God as both explanation and answer, as if the past were a black hole in the wall of our cozy little house disturbing us with its vastness each time we walk past it. (The darkness of space and deep time is a frightening thing to behold and it sends a chill up our back each time we think about it). So it’s little wonder that we sometimes hang an image called “god” over the hole to cover it up — to get it out of our mind. But that action does nothing to answer the question and it doesn’t make the past eons go away (for even the concept of “god” makes us consider infinity and eternity). And so time (on this scale) is something we cannot escape.
So, if we can’t escape it and if we can’t cover it up, what do we do with it? We work towards a way of understanding it.
And we need to understand it, for there are many who doubt evolution because they can’t see it happening in the time scale of their own lives. They wonder why they don’t see monkeys at the zoo changing, day by day, into humans. To this we have to explain two principals from the theory of evolution:
The first: INDIVIDUALS DON’T EVOLVE: POPULATIONS DO. The inherited traits and genetic mutations that make up the process of evolution occur as organisms reproduce and create new offspring: genetic mutations accumulate over time as environment and the challenges of daily living naturally select the individuals that are most suited to survival in a given place and time.
The second: TIME. Small changes in each generation over many, many generations lead to dramatic changes in the traits of living organisms: Whales evolved from four-legged animals that walked on land and modern birds evolved from dinosaurs.
Wildly impossible feats if you think that the earth and all its creatures have been around for only six thousand years. But once you realize just how much time life had to get started, and then how much time it had to evolve, evolution can at last be appreciated for the astonishing explanation it supplies us for understanding life on earth. So let’s try to understand just how long this has been going on.
I will try to assist by using some of the tools that I used to understand geologic time. To do that I will use three pieces of lumber and a tape measure.
Let’s imagine laying three 8-foot long 2×4 boards end to end. That gives us 24 feet of lumber for our “timeline”. The “big bang” that spawned our universe occurred some 13,000 million years ago, but our earth formed only 4,500 million years ago, so let’s start with that number and divide 4.5 billion (or 4,500 million years) by 24. Now, each foot of lumber represents 187.5 million years starting on the left end (at 4.5 billion years ago) and ending at the right end (the present).
At the tip of the first board, the earth begins to form (4,500 mya); where the first board meets the second board, earth’s first landmasses form at about 3,000 mya.
So, we’re already on the second board. Where is life?
There is fossil evidence to suggest that light-reactive bacteria were around as early as 3.8 billion years ago – which means it may have begun evolving as much as 4 billion years ago. But, the earliest definitive fossil evidence for complex, multi-cellular life shows up at 1.2 billion years ago. (Another 6.4 feet onto the second board).
So from the earliest dated rock to the earliest definitive fossil of a complex cell: Three point three four billion years pass. Three thousand three hundred and four thousand million years (more than half of our “timeline”) passed for life to begin (or 18.13 feet from “the beginning”)
Six hundred fifty-seven million years later, during the “Cambrian Explosion” life starts developing shells and hard parts. (580mya, or only 3.93 feet from “today”).
Fifty million years after that (or about 3.2 inches): the first known footprints are made on land.
Another three inches or so (or 55 million years later): Primitive plants appear (followed later by insects, sharks and seed-bearing plants).
Then about 290 million years ago: (a foot and a half from today) Dimetrodon – a pre-mammalian reptile — leaves his muddy footprints on the Permian shoreline. But then: (252 mya 2.5 inches later) The Permian-Triassic extinction event. 70% of all life on land and 95% of life in the oceans are wiped out.
Life recovers. Like it probably had before, the fossil evidence suggesting this was not the first major extinction event. Life recovers in a big way.
THE AGE OF THE DINOSAURS
The impressive one hundred sixty-five million year reign of dinosaurs covers about 10.25 inches of board.
That means that a Tyrannosaurus Rex living in the late Cretaceous (the last of the Dinosaurs) could have tripped over the fossil of a Jurassic Stegosaurus that had been extinct already for millions of years. Dinosaurs were walking on the fossils of earlier, extinct dinosaurs.
During their reign the first viruses appear, as do flowering plants.
Then 65 mya (About four and a half inches ago): The Cretaceous-Tertiary (KT) Extinction event. Dinosaurs and about ½ of all species are wiped out.
35mya Grasses evolve.
About 5 million years ago we split off from our last common ancestor with the other primates (and no, Evolution doesn’t say we descended from a chimp — that would be like saying you descended from your own distant cousin — but it does show chimps and humans shared a distant common ancestor).
Then — some 200,000 years ago — the first anatomically modern humans appear (us without a shave and a suit).
50,000 years ago we inhabit Europe.
25,000 years ago the last of the dead-end branches of our hominid family tree, our distant cousins the Neanderthals die out.
10,000 the Neolithic: Our modern history begins. Tools, art, language, and then you and me.
After 4.5 billion years of bubbling, rumbling, profligate evolution and extinctions (large and small) here we are — our entire human history occupying less than the last 1/64th of an inch of earth’s 24 feet of history.
So that’s how long it took for us to get here. That is how much time life — you and I — had to evolve.
I hope this helps you understand evolution, and helps you appreciate how amazing it is to be alive right here and right now.
– the not-so-reverend bob