The dynamic changes and developments in the universe have been going on for a long time. In chapter 5 we described how geologists, over the past three centuries, have accumulated many kinds of evidence from rocks that the earth is billions of years old. In a similar fashion, over the past century astronomers have studied planets, stars, and galaxies and have found many strands of evidence that the universe is billions of years old. This consensus of astronomers is based on many independent measurements and has stood the test of time, a good indication that these results are reliable. In this section we’ll describe some of this evidence for the great age of the universe.
Evidence from the Size of the Universe
Evidence from the Moon and Planets
Studies of the Moon and planets also give evidence for great age. Geologists can use some of the same methods to measure the age of rocks on the Moon, Venus, and Mars as they use on Earth. That’s because the asteroid collisions, volcanoes, and erosion they observe on Earth also occur on the Moon and planets. Photos taken by spacecraft while orbiting Mars show channels and gullies on the planet’s surface. Similar channels on Earth are usually made by flowing water. Yet there is no liquid water on the surface of Mars right now.What does this have to do with age? It is evidence that Mars was much different in the past than it is today. The atmosphere used to be much thicker and warmer, similar to Earth’s, but now it is much colder and thinner. This dramatic change in planet-wide climate took millions or billions of years. Thus the rocks testify that the planet Mars must be at least this old.
Evidence from the Orbits of Asteroids
The orbits of asteroids also show evidence of a long history. When an asteroid is discovered, its path through the sky shows its orbit around the Sun. Once astronomers know the orbit of an asteroid they can calculate its orbit in the past and into the future to see whether it will hit the earth. By calculating the orbits backward, astronomers have found several asteroids that converged at the same location several million years ago. Apparently two larger asteroids collided at this spot and shattered into the smaller asteroids we see today. If God had created asteroids just a few thousand years ago, why would he have put them in orbits that suggest a collision several million years ago? The evidence clearly points to a long history for asteroids.
Evidence from Meteorites
Radiometric dating is used to study rocks on Earth as well as rocks from elsewhere in the solar system. Studies have been done on the rocks that astronauts brought back from the Moon and on asteroids that have fallen to Earth. As with Earth rocks, scientists use multiple radioactive isotopes to cross-check age measurements. At least three different isotopes have been used to measure the age of Moon rocks, and at least five different radioactive isotopes have been used to measure the age of meteorites. The results all agree: the oldest Moon rocks and asteroids are 4.6 billion years old. This is our best measure of the age of the solar system as a whole. The universe itself must be at least this old.
Evidence from Star Clusters
Another important measure of age in the universe comes from star clusters. Because all stars in a star cluster form in the same nebula at about the same time, they all have about the same “birthday.” But they don’t all have the same lifespan. High-mass stars burn bright and fast like a “flash in the pan,” while low-mass stars burn slowly and steadily. Consider how this will look in a star cluster. A cluster starts with many stars with the same birthday but of all different masses. Over time the high-mass stars die off first, leaving behind the low-mass stars. This means that if many high-mass stars are present, the cluster must be young because they haven’t burned out yet. If most of the stars are low-mass, the cluster must be old. Careful studies of star clusters show that some clusters are younger and some are older, with the oldest ones having an age of about 12 billion years.
Multiple Lines of Evidence
The most distant galaxies, the planets and asteroids of our own solar system, and the oldest star clusters all are several billion years old. Astronomers have many different methods for measuring the age of various objects, and they all support ages of billions of years, not thousands. Even if the assumptions of one or two methods were faulty, it is highly unlikely that all of the methods would be affected. Like the geologists in the 1700s, astronomers today have found multiple lines of evidence against a young earth and young universe.It may seem as though we are once again describing a conflict between science and theology. Scientific results that indicate great age do conflict with the Young-Earth Interpretation of Genesis 1 discussed in chapter 5. But remember that in chapters 5 and 6 we presented many other interpretations of Genesis 1; several of these are notin conflict with the great age found in the book of nature. In chapter 6 we also explained why we believe that the best biblical scholarship, quite independent of modern science, indicates that Genesis 1 was never meant to convey scientific information to the original audience. Its intent for the first listeners, and for us, is to teach the who and why of creation, not the how and when. Taken in this context, there is no conflict between Genesis 1 and the astronomical evidence for great age.