The age of the earth is important in framing an interpretation of the early chapters of the Bible. Genesis 1 describes the creation of the heavens and the earth, and the formation of earth’s life forms, in six “days”, which were demarcated by “evening and morning”.
Early Christian writers held various opinions on the length of these days. Some (e.g. Basil) believed them to be 24-hour days, some (e.g. Cyprian) held them to be 1000-year periods, others (e.g. Origen) to be allegorical only, while Augustine opined that it was difficult to be sure about what the “days” of Genesis actually were.
Today’s Young Earth (YE) creationists typically take them to be normal 24-hour days, and also take the genealogies in Genesis and elsewhere in the Bible to be literal and exhaustive representations of post-creation chronology. This leads to a Creation about 6000 years ago, with nearly all the observed sedimentary rock layers deposited in a 1-year Flood about 4500 years ago (~2500 B.C.).
Bible literalists often claim that a recent creation and Fall of a literal, sinless Adam and Eve is essential for the Christian gospel. That assertion is not remotely true. Nowhere in Jesus’ teachings or in the apostolic preaching in Acts is the Fall ever mentioned, and Paul develops his doctrine of the universality of sin in Romans 1-3 quite apart from Adam. (See here for more on Adam and the Fall and evolution).
When young Christians are taught that a young earth is an essential part of Christianity, this can and does cause some of them to lose their faith when they later encounter the evidence for an old earth in geology or biology classes. Thus, we should be cautious about asserting that one Bible interpretation is the only valid approach.
Other Christian viewpoints are compatible with the ancient earth which science reveals. Old Earth (OE) creationists are willing to accept that the earth is billions of years old. They often take a flexible approach to interpreting the verses of Genesis 1-3, trying to identify the “days” with various epochs of geological history (“Day-Age” approach). Other Old Earth interpreters suggest that the six “days” of Genesis 1 are not 24-hours days when creation actually took place. Rather, they are six successive days when God showed visions to Adam or Moses of what happened long before in creation. Another suggestion is that these “days” reveal six groups of divine creation proclamations (“let…”), while the outworking of those proclamations occurred sometime later, possibly through natural means.
The Reasons to Believe site lists about 40 well-known, impeccably conservative Christian leaders and writers that endorse or are at least open to an old-earth perspective. These include names like Gleason Archer, Michael Behe, Chuck Colson, Norman Geisler, Hank Hannegraff, C. S. Lewis, Francis Schaeffer, C. I. Schofield, Lee Stroble, and B. B. Warfield. Ditto for John Piper.
Evolutionary creationists, sometimes called theistic evolutionists, believe the earth is old and also accept that God used macroevolution to bring about today’s living creatures. They recognize that in the Bible God often used stories which were not necessarily true to communicate spiritual truths. Thus, the Genesis narrative may function much like the parables of Jesus, or the story that Nathan told David about the poor man’s lamb. Essentially all Roman Catholics, and nearly all evangelical Protestants who are practicing geologists or biologists, are evolutionary creationists.
Advocates on both sides of the age issue present long lists of physical evidence. Here I will mention a few that are relatively straightforward, not requiring scientific training to understand.
There are many spots on earth where you can observe rock layers with this sort of pattern:
There is a lower set of rock layers, often steeply tilted, overlain by an upper set of layers which meet at a different angle. This is called an angular unconformity. A classic example of an angular unconformity is at Siccar Point, in Scotland:
This shows the erosional interface between steeply tilted layers of “greywacke” rock, topped by nearly horizontal layers of conglomerate and the distinctive Old Red Sandstone. By 1800, European geologists had realized that this sort of formation required the following sequence of events:
(1) Thousands of feet of sediment accumulated underwater to form what we now see as the greywacke. Even more sediment was laid down on top of that, to compress and cook it to form solid rock layers. Such sediments typically derive from the weathering of pre-existing rocks on land, so it would take many years to produce all the sediments we see in the rock layers around us.
(2) This whole assembly was tilted and raised above sea level.
(3) Hundreds of feet (meters) of solid rock were eroded away to form the top surface of the greywacke that we now see as the unconformity. We know the greywacke was solid (not just recent, soft flood deposits), because broken-off chunks of the greywacke are found in the conglomerate layer just above it.
(4) The greywacke then sank below the waters, and many more feet of sediment were deposited, starting with the conglomerate and the Old Red Sandstone, then more layers on top to lithify them.
(5) Finally, this formation was again lifted above sea level, and many feet of the overlying rock were eroded away to form the present land surface in that area of Scotland.
All of these events cannot be fitted into a one-year Flood, or any reasonable reconstruction of a 6000-year-old earth.
In some cases, there is an erosional surface between two rock layers (e.g. C and D, in the figure below) which are nearly horizontal:
Because both all layers are flat, it may not be immediately obvious that there was a time gap between their depositions, so geologists have to look closer for more clues. Often, the presence of hard, loose pebbles of a lower layer (“Layer C”, here) embedded in valleys at the C-D interface demonstrates that the lower layer had hardened into solid rock and then was eroded prior to deposition of the upper layer. Thus, such a location must have gone through the same cycles of deposition/ lithification/ uplift/ erosion/ subsidence/ deposition/ lithification/ uplift/erosion as with an angular conformity.
In places, two or more unconformities are found among successive layers, making it extra clear that these layers were not laid down in a single, year-long Flood. For instance, in the Grand Canyon, at least three distinct disconformities are found among the main visible horizontal layers, along with a dramatic angular unconformity at the base of these layers. Unconformities in the Grand Canyon rock layers are treated more thoroughly here.
If you want to stop reading now, this above is all you really need to know about the evidence for the age of the earth. There just is no reasonable way to fit these observations into a young earth scenario. On the basis of evidence like this, essentially all practicing geologists, many of them evangelical Christians, had concluded by 1840 (long before Darwin published On the Origin of Species) that the earth must be at least several million years old.
However, with passing decades, more observations have confirmed the great antiquity of the earth. Some of these observations are discussed below.
Fossil Soils and Animal Burrows in the Midst of Rock Layers
In Flood geology, the main sedimentary rock layers were all laid down in a one-year Flood. Where these layers are many thousands of feet deep, the rate of deposition must have been very high. Arguably the sea level may have sloshed back and forth, occasionally exposing the surface of the sediments and leading to variable deposition rates, but something like a foot an hour would be a typical average rate for the Flood year in many areas of North America. That leaves no time for deep soils to build up from rock weathering in the middle of Flood deposits (i.e. in the middle of the Flood year), or for terrestrial animals to dig deep burrows in that soil.
Yet just such soils and burrows are found in the midst of thousands of feet of sedimentary rock layers (see here, here, and here). Such ancient, buried soils are called “paleosols.” Here is an example of a well-developed paleosol (the brownish layer across the middle of the photo) in the Morrison formation which dates to about 150 million years ago and is centered in Colorado and Wyoming. In this layer are whitish fossilized burrows made by vertebrates. All this simply could not happen under the raging sea while many feet per day of sediment are raining down, and thus the existence of these paleosols and burrows invalidate the notion that the sedimentary rock layers were deposited during a recent worldwide Flood.
As with the unconformities described above, only a long sequence of events can account for this formation. Again, thousands of feet of sediments were deposited, covered by more sediments, to turn them into rock. Then this formation was lifted above sea level by plate tectonic motion (which we now know to be huge, over time), and the rocks eroded down. Erosion formed a layer of soil, and some animals lived there and dug burrows. Later this area got covered with water again, and more thousands of feet of sediment were deposited, and eventually turned to rock. Once again, this area was raised out of the sea and the solid rock eroded down to the present level.
Massive Salt Deposits in the Midst of Rock Layers
In many locations (see map below) there are huge salt deposits, hundreds or thousands of feet thick, laying under thousands of feet of sediment. These salt deposits were formed over many thousands of years, from the evaporation of shallow coastal lagoons or of vast inland seas. These evaporations occurred after the deposition of lower rock layers, and before the deposition of further rock layers above. This could not happen in the middle of a year-long Flood.
Thick Limestone Layers, Caves, and Fossil Reefs Among the Rock Layers
Limestones are deposited by the slow raining down of shelly organisms as they live and die, in a mainly clear body of water where sand and mud sediments are not being brought in to commingle with the animal shells. For instance, limestone formations are depositing in some areas of the Caribbean, where there are no major continental rivers dumping sand or silt into the ocean nearby. In many areas of the earth, in the midst of other rock layers, there are over a thousand feet of limestone deposits. These limestones would require many years to form, in relatively clear, calm waters. They could not have been deposited in the midst of a raging, worldwide Flood.
After the shelly remains have has been consolidated into limestone rock, and that rock has been raised by tectonic forces above sea level, slightly acidic (freshwater) rain from the atmosphere can seep into it and erode channels and large caves. Sometimes these caves reach up to the land surface, which then collapses into the cave to form a sinkhole. Such cave formations are found by geologists with hundreds of feet of sedimentary rock layers above and below them. This all takes many thousands of years to happen, and could not occur in middle of a year-long global Flood. For instance, Davis Young writes of the Redwall Limestone, which is near the middle of the Grand Canyon rock layers:
Still another indication that the Redwall was exposed to the atmosphere for a lengthy period of time – far more than a year – is the existence of caverns beneath, and of sinkholes in, its upper surface. The caverns and sinkholes are commonly filled with red shales from the overlying Supai Group or with angular blocks of fragmented Redwall. [Davis A. Young, Portraits of Creation, ed. H.J. Van Till, et al., Wm. B. Eerdman’s, Grand Rapids (1990), pp.68-69.]
The sustained growth rate of a coral reef is about 8 mm or 0.3 inch per year. The Eniwetok Atoll in the Pacific is over 1380 meters or 4600 feet ( =55, 000 inches) deep, so it is at least 180,000 years old, and probably much older. Its features show that this atoll is indeed grown-in-place coral, not (as argued by YE creationists) the result of some Flood deposition.
Geologists have discovered many fossilized reefs deep down among the sedimentary rock layers. The porous nature of these fossil reefs makes them important reservoir rock in oil fields. Daniel Wonderly, after discussing the modern Eniwetok Atoll, describes a set of fossil reefs over 800 ft thick, which lie among thousands of feet of other sediments in a Canadian oil field. In the YE creation model, these reefs lie among sedimentary layers laid down by Noah’s Flood, but it is not possible for thick coral reefs to grow in the middle of year-long Flood.
Tens of Thousands of Annual Layers (“Varves”) in Lake Bed Sediments
In some lakes in northern latitudes, there are patterns of light and dark layers of sediment. Analyses of their composition (e.g. pollen from nearby terrestrial plants in bloom, and carbonate from tiny shelly organisms) establish that each pair of layers corresponds to the passage of the seasons of one year. In one lake near Interlaken in Switzerland, these layers can be traced back undisturbed at least 9,400 years.
Lake Suigetsu in Japan is an ideal locale for annual varves, being sheltered from storms and from gross river deposits. The varves in Lake Suigetsu have been counted to more than 60,000 years ago. As described by Natural Historian these varves have been cross-correlated with carbon-14 dating, and by dating of ash-falls from known, ancient volcanic eruptions, which confirm their yearly nature. The figure below is drawn by Davidson and Wolgemuth, and shows agreement between the carbon-14 dating of the varves sediments taken from two different lakes, and the carbon-14 dating of the annual growth rings in the trunks of ancient trees. Their caption on this figure reads:
Tree-ring number (solid line) and varve number (circles) vs. measured carbon-14. Varves less than 5000 are from Steel Lake, Minnesota; varves greater than 5000 are from Lake Suigetsu, Japan.
“Measured carbon-14” is shown as the natural log of the carbon-14 activity. Vertical bars represent the magnitude of uncertainty in the measured value. Data comes from references in footnotes 6 and 7.
The data from growth rings in tree trunks in this graph extends back more than 10,000 years, and serves as confirmation of the overall soundness of carbon-14 dating, and also as a means to estimate ancient atmospheric carbon-14 levels to make minor calibration corrections to the carbon-14 dating.
These varves were laid down in relatively undisturbed lakes, and thus invalidate the notion of a raging worldwide flood which occurred in 2500 B.C. YE advocates have no valid response to this. They attempt to point to examples of some other lakes where storms or other factors caused more than one pair of light/dark layers being deposited in a year, but this is irrelevant. Geologists are well able to distinguish annual layering from storm layers using a variety of tests, and the analyses of the layers in Interlaken and Lake Suigetsu clearly show them to be annual.
The figure below shows the difference between random storm varves (on left) from Lake Walensee in Switzerland, and the regular laminations seen in yearly varves from Lake Zurich.
Further discussion of the validity of varves for dating is here.
Hundreds of Thousands of Annual Layers in Arctic and Antarctic Ice Cores
Cores of ice, hundreds of feet long, have been drilled out of glaciers in Greenland and Antarctica. Summer/winter layering can be discerned in them. The GISP2 core from Greenland has been counted back at least 110,000 years, using the corroboration of two to three independent methods. Antarctic cores go back more than 400,000 years, quite undisturbed by any world-wide Flood. At least nine different methods were used to date the layers of the Antarctic cores.
Hugh Ross comments:
How do scientists confirm that these ice layers correspond to years of Earth’s past history? They can check for telltale markers, such as volcanic ash signatures. The Krakatoa eruption of 1883 and the Vesuvius eruption that wiped out Pompeii and Herculaneum in AD 79 left their specific marks in exactly the annual layers anticipated. Climatic cycles also allow for testing. As it turns out, these cycles-caused by regular variations in the eccentricity or ellipticity of Earth’s orbit (period = 100,000 years) and the tilt of Earth’s orbit (period = 41,000 years)-correspond perfectly with what’s seen in those core layers. Finally, researchers have performed radiometric dating of minerals embedded in the ice to make sure their age corresponds with their annual layer, and in each case it does.
For example, at the right of this photograph of a 22-inch section of a Greenland ice core is a dark brown volcanic ash layer that occurs at about 55,000 years down according to annual ice layer counting. Analysis of its contents shows it to be the same as the “Z2” ash layer which has been widely found in Atlantic ocean floor sediments and independently dated to 55,000 years.
YE creationists argue that these are not really annual layers in the ice, but are due to a succession of storms within just a few years. The Western Geologist and Old Earth Ministries show why these arguments fail.
Some World War II era airplanes which landed on a Greenland glacier are now covered in many meters of ice. YE creationists note a discrepancy between that rate of ice accumulation, and the much slower (in terms of centimeters per year) ice accumulation in the Greenland cores. However, that difference in rates is expected: the airplanes landed near the coast, where snowfall in much higher and the glaciers flow more, whereas the cores were deliberately drilled near the center of Greenland, where the glacier does not move much and where the snowfall is lower.
Further Evidence for an Old Earth
I tried to pick out some observations above which would be clear for both scientists and non-scientists alike. There are yet other evidences that the earth is millions or billions of years old, which may require more thinking through. Some of these are described in the links below, listed roughly in order from shorter to longer articles.
How are the ages of the Earth and universe calculated? [Biologos] About two pages. Treats very diverse (geology and astronomy) methods to date the earth and the universe
How Do We Know the Earth is Old? (Infographic) [Biologos] This infogram packs brief descriptions of ten different dating methods , with lots of illustrations, into about two pages. Excellent for those who are new to this whole topic or who have short attention spans.
What evidence is there for the earth being billions of years old? [by Russell Downs at BibleQ.net] Brief discussion of radioactive dating of rocks, answering objections raised by YE creationists.
Christian Geologists on Noah’s Flood: Biblical and Scientific Shortcomings of Flood Geology – – Clear, illustrated discussion of salt deposits, ordering of rock layers and fossils, tree rings, and varves, by geologists Gregg Davidson and Ken Wolgemuth of Solid Rock Lectures.
Scientific Evidence for an Old Earth [Reasons to Believe] Articles include:
Deep Core Tests for the Age of the Earth
Multiple Lines of Evidence Support an Ancient Earth
The Age(s) of the Continents
Helium Diffusion in Zircon: Evidence Supports an Old Earth, Part 2 (of 2)
Radiometric Dating A Christian Perspective – – This is a classic, in-depth discussion of radioactive dating of rocks, on ASA website.
Evidence against a recent creation [Rationalwiki] – – covers many topics, as listed below