From their Science Speaks Newsletter they lay down the gauntlet:

It is our assertion that there are no valid young-earth arguments - not even one. Whether scriptural or scientific, they all contain errors. If there is even one valid argument which actually proves the earth is young, we still haven't seen it. We challenge any young earther to demonstrate otherwise.

It's not that anyone can claim they are not "Christian" enough - their agenda, sounding like many on the far political/religious right, is clear:

God's creation testifies of its great age. If we hope to regain credibility, win court cases, and influence our country, then we Christians need to speak the truth. The goal of the Science Speaks Newsletter is to examine evidence and answer questions. We believe that the young earth position is insupportable and that all scientific and Scriptural issues are better answered in the context of an old earth.

In other words, they feel the need to discredit the anti-science extremists within their own community if they are to gain traction with Americans on issues that are most important.

Excerpts from author Dan Stone include "Old Earth Evidence I, Annual Layers," which argue for basic common sense within the Christian community otherwise propagandized by their own anti-science crowd, using anecdotal examples:

God created his universe with many built in ways of knowing its age. There are many natural processes which keep an actual count of passing years. The first of these we learn about, often as children, is that we can tell how old a tree is by counting its annual rings.

It is easy to understand why this works. When a tree grows, it adds wood to its outside layer just under the bark. Trees do most of their growing in the spring and summer and sit dormantly through the winter. This means that wood is added to the outside of the tree in spurts once a year. These annual growth spurts are visible as rings in the grain of the wood. By examining these rings, we can see many things such as which years had what sort of weather and during which years fires occurred.

Some trees live for very long periods of time; Bristlecone pine trees, which grow in the White Mountains of California, live for many thousands of years. One lived over 5000 years before it was, unfortunately, cut down in 1964. Now 5000 years is not the age of the earth; it is merely the age of one tree in California. Obviously, the soil and rocks which were under that tree are even older.

Like trees, sediments which accumulate in the bottoms of lakes also keep a yearly record of time. Different seasons create different types of sediments. In spring and summer, they are rich in calcium carbonate (limestone) which dissolves in the water from melting winter snow. The rest of the year, sediments are rich in organic material. This creates visible annual layers which stack up year after year.

The Green River Formation, of Utah, Colorado and Wyoming, is made of sediments from a huge fresh water lake which once occupied that location. It contains more than four million annual layers. This means that the lake existed for millions of years before it disappeared. This is still not the age of the earth; it is only the length of time one particular lake existed. Once again, the rocks which lie under these layers, including all of the dinosaur fossils and all of the layers in the Grand Canyon, must be older yet.

There are many other examples we could examine. God has left a great deal of detailed and consistent evidence for the age of His creation. Scientists who study this evidence don't just think God's creation is old, they know it is old.

While constant references to God in every discussion (including science) may not be my style or belief, it is for millions of moderate Christian Americans (especially the home schoolers). This web page includes links and references to their publications and articles from others for this "common sense science" argument within a Christian, Jesus-centered context. They don't want the non-rationalists to give them a bad name, either, and don't feel it's OK to lie just to prove a story.

So don't buy the argument that "Young Earth" is the only Christian interpretation.