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International Planetarium Society *

Many independent lines of scientific evidence show that the Earth and Universe are billions of years old. Current measurements yield an age of about 4.6 billion years for the Earth and about 14 billion years for the Universe.

How ages are measured

The age of the Earth is measured by studies of radioactive elements. Radioactive elements are unstable and "parent" atoms decay into other "daughter" elements at a steady rate. For example, through a series of steps, atoms of uranium decay into atoms of lead. By measuring the abundance of "parent" and "daughter" atoms in rock samples and knowing the decay rate, geologists can calculate the age of the rock. Using several different sets of parent and daughter elements, geologists have measured the age of a variety of rocks, including terrestrial and lunar rocks as well as meteorites, which originate primarily from asteroids. The results consistently indicate an age of about 4.6 billion years for the Earth.

The age of the Universe is measured in several ways. One method is based on the rate of expansion of the Universe. By measuring the distance to remote galaxies and the rate at which they are expanding away from us, astronomers can calculate how much time the galaxies have needed to get as far away as they are. This tells how long the Universe has been expanding, or how old it is. These studies yield an age of about 14 billion years.

The age of the Universe can also be determined by investigating the oldest clusters of stars. This is done by measuring the brightness and temperature of stars in a cluster and comparing those measurements with models of how the brightness and temperature of a star change as the star ages. It is somewhat like estimating the age of a person by looking at features of his or her face and knowing how our faces change as we age. These studies show that the oldest star clusters are about 12 billion years old. The Universe must be older than its stars, so this method establishes a minimum age for the Universe. Similar studies show that the Sun is about 5 billion years old, consistent with the age of the Earth measured by radioactive studies.

A third way to determine the age of the Universe involves measuring the ages of long-lived dying stars. As stars like the Sun age, they eventually become very small, faint objects about the size of the Earth. These stellar corpses are called "white dwarf" stars and have no remaining sources of new energy. Astronomers can calculate the rate at which white dwarfs get fainter and cooler, so when they then measure the brightness and temperature of a white dwarf star, they can recognize how old it is. These studies show that the oldest white dwarf stars are at least 10 billion years old. As above, this establishes a minimum age for the Universe since the Universe must be older than its stars.

Why these measurements are accepted by the scientific community

These measurements of age are accepted by nearly all astronomers, including both research astronomers and planetarium educators. These astronomers come from nations and cultures around the world and from a very wide spectrum of religious beliefs.

A fundamental reason why these ancient ages are so widely accepted by the scientific community is that they are derived from several independent lines of evidence accumulated by independent and often competing teams of researchers. Each method involves different measurements and the application of different physical principles to derive ages from those measurements. The physical principles include the same thoroughly-proven principles that underlie the technology that runs the modern world. Hence the fact that the independent methods all yield similar ages reinforces confidence that the methods are sound and accurate despite their complexity and do not contain major fundamental flaws.

A second reason why these ages are so widely accepted is that for scientific results to be published in research journals, they must be critically reviewed by other scientists who are experts in the same research area. This process is called peer review and is employed in nearly all research journals in the physical and biological sciences and in the humanities and social sciences. Often the reviewers are competitors of the author and thus are especially keen to find flaws in the proposed publications. As a consequence of such review, nearly every paper must be revised and improved before it is published, and some papers are rejected because the review exposes flaws in the measurements or in their analysis and interpretation.

A third reason why these ages, and other scientific paradigms such as Einstein's theory of relativity, are so widely accepted is that by the nature of its acquisition — through independent lines of evidence and always subject to scrutiny — scientific evidence is built up only very slowly, one step at a time. Only when a very large and diverse body of evidence has been accumulated is a broad conclusion accepted. Even then, a broad conclusion remains subject to inspection, as further evidence may reinforce or refine it, or in rare cases, overthrow it.

Conclusion

Evidence that the Earth and Universe are billions of years old is based on diverse lines of research that have been rigorously examined and which yield concordant results. Therefore, IPS accepts that these results provide an accurate description of our Universe.

Planetariums are based on science and education and as such reflect the ideals and principles of these disciplines. Planetarium educators seek to present both scientific results and an understanding of how these discoveries are made. IPS respects the personal views and opinions of planetarium patrons and of individual planetarium educators and recognizes that in some cases those views may differ from the material presented in this statement.

Related statements

The American Astronomical Society has a statement on the age of the Universe on its web site at http://www.aas.org/governance/council/resolutions.html#create. It has also, in conjunction with the Astronomical Society of the Pacific, published a booklet An Ancient Universe: How Astronomers Know the Vast Scale of Cosmic Time. This booklet is available in PDF form at www.aas.org/education/ancientuniverse.html.

The American Physical Society has a statement on creationism on its web site at www.aps.org/statements/81_1.cfm and a statement on the nature of science at www.aps.org/statements/99_6.cfm.