Fossils provide a window into the distant past, revealing how life has changed across vast periods of Earth’s history. The arrangement of fossils within rock layers and across the world is highly ordered, and transitional fossils are abundant. While fossil evidence alone does not prove that all life forms are related by common ancestry, the fossil record is consistent with (and highly suggestive of) that conclusion. Predictions about where transitional fossils should be found—made on the basis of common ancestry—have yielded stunning discoveries. For Christians, the fossil record is a remarkable gift that prompts reflection on the kind of world God has made.
Fossils are rare, plentiful, and diverse
Fossils are the remains or traces of ancient organisms, preserved over the ages in rock, amber, tar, ice, or another medium. Scientists who study fossils, called paleontologists, use a variety of techniques to reveal what an ancient organism looked like, where it lived, what it ate, and how it behaved.
Today, we take for granted that a fossilized tooth or bone came from a creature that lived long ago. But that wasn’t always true. In the 1600s, as fossils began to be systematically studied, there was vigorous debate about how to interpret them. Some argued they were not remnants of living things. This was because fossils were made of stone—the same kind of stone as the surrounding rocks, not bone or tooth or shell—and because there was no known mechanism for how they could be buried so deeply within the earth. Furthermore, fossils frequently did not resemble any living creature, and at that time it was widely believed that species were “fixed,” or unchanged since their creation. Extinction was not believed possible. By the late 1600s, however, arguments that fossils are in fact the hardened remnants of past life began to win the day. Devout Christians such as John Ray and William Smith played an important role in describing and understanding the true nature and distribution of fossils. These early Christian geologists saw God as creator of these life forms that lived in distant ages past.
Fossilization is an extremely rare event, but fossils are plentiful. How can this be? The likelihood of fossilization depends greatly on local conditions and the makeup of the organism. After they die, most organisms are eaten or decompose quickly because they are exposed to the air. In order to become fossilized, organisms must be preserved in low-oxygen conditions (oxygen feeds the bacteria that break down dead organisms). An insect stuck in tree sap; an Iron Age man trapped in a bog; a dinosaur swept downriver and buried in sediment from a flood—these are rare events, but because life has existed for so long, and so many creatures have walked the face of the earth, we now have massive collections of fossils spanning most of Earth’s history. The oldest fossils, microbial mats in Greenland, are 3.7 billion years old!
The majority of fossils come from creatures with hard body parts like teeth and bone, but there are many other kinds of fossils, too. A mammoth frozen in ice can be preserved with remarkably little degradation for tens of thousands to millions of years. Scientists have found pristine, individual leaves pressed in ancient lakebeds, sometimes with the original pigment intact until exposed to air. Other examples include dinosaur skin, feather impressions, pollen, invertebrate crawling traces and burrows, shells, dinosaur nests with preserved eggs, and “petrified” (paleontologists prefer the term permineralized) wood. Scientists have even discovered soft tissue preserved inside fossilized dinosaur bones! The processes by which these different types of fossils form, called taphonomy, is an exciting area of study within paleontology.
Fossil distribution in sedimentary rocks is highly ordered
Fossils are most often found in sedimentary rocks, rarely found in igneous rocks (those formed from magma), and almost never found in metamorphic rocks (those altered by heat and pressure). Sedimentary rock forms when mineral and organic material is laid down and eventually cemented in layers called strata. Sometimes this can occur rapidly, but it typically takes millions of years for appreciable layers to form.
In most cases, older strata are found below younger strata, just as last week’s newspaper will typically be found under today’s junk mail in the recycling bin. Geologists call this the principle of superposition. Over time, beds of rock may be tilted, folded, broken, or otherwise disturbed. Yet scientists can often determine the likely sequence of events that led to these results. The fossils in each layer of rock are thus a sampling of the kinds of organisms that lived in those environments when the layers formed. In this way, strata are the “pages” of a book about life’s history that can be read and interpreted.
Fossil distribution is strikingly ordered in several ways. Long before Darwin’s day, it was observed that various types of fossils were always found together relative to others within a column of rock. That is, some kinds of creatures were found with each other and not with others. Trilobites are found in lower, older layers; giant insects and ferns higher up in younger layers; dinosaurs higher still in even younger layers; and so on. The order of fossil groups in different layers is highly consistent from place to place—even across continents. This pattern of one group of fossils seemingly being replaced by another is so consistent that it became known as the principle of faunal succession.
Faunal succession not only shows evidence of extinction (even large-scale or mass extinction events, in which up to 90% of species were lost) but also evidence that new species routinely come into existence. While both ideas were surprising in the 1800s, they are widely accepted today, even among those who contest the theory of evolution.
Some Christians today believe that all fossils were laid down several thousand years ago in Noah’s Flood (Gen 6-9). If this were the case, we would expect fossils of all types to be mixed together. But never do we find trilobites and flowering plants in the same layer, nor a single dinosaur in the Grand Canyon (though they are found, as expected by the age of the rocks, in higher layers in the adjacent Grand Staircase formation). The fossil record clearly testifies (along with other geological evidence) that there has never been a catastrophic, global flood event. Yet that does not mean there is no historical basis for the Flood story. The biblical account may be called theological history: that is, it describes real events (perhaps a regional flood event) in highly figurative language for a theological purpose. Many Bible scholars and scientists who are committed to the inerrancy of Scripture reject Flood geology for both biblical and scientific reasons.
Fossils also display order in other ways. Not only are certain layers of rock identifiable the world over by the fossils they contain, but moving up a column of rock, one can see a trend toward larger organisms within lineages. The size trend only works within lineages, not between them: mammals get larger as you move up, but are not larger than dinosaurs. Furthermore, small organisms are present in every layer, but no large animals are found at the bottom. These trends are difficult to square with Young-Earth Flood geology but are exactly what one would expect if rock layers took millions of years to form and if life forms are related by common ancestry.
Transitional fossils are plentiful
Many critics of evolutionary theory cite a lack of “transitional fossils,” which represent the evolutionary transition from one species to another. In one sense they are right: for a number of reasons, it is rare to find a fossil that can be definitively assigned to the lineage between two other known species. An analogy helps to show why: If you picked a grave at random from a family cemetery, it is unlikely that you would find the burial place of your great-grandfather (your direct ancestor), but very likely that you would find one of a distant cousin (your family, but not your direct ancestor). Because of the “bushiness” of the evolutionary family tree, there can be many closely-related species that are not direct ancestors of one another.
True transitional forms are thus expected to be extremely rare. More common, in theory and in practice, are species that are evolutionary “cousins.” They are still considered to be transitional because they share a close common ancestor with both groups. Archaeopteryx is a classic example—it represents the transition from non-avian dinosaurs to birds, but is not the direct ancestor of any birds alive today.
Scientists have found many, many possible transitional fossils. They are abundant for so-called “microevolutionary” transitions, but they are also present at each major hypothesized evolutionary transition. Sometimes entire sequences of transitional fossils are known. These major transitions include one of many lineages of fish adapting to land, a lineage of early theropod dinosaurs evolving flight, land mammals adapting to a marine habitat, and one lineage of primates into humans. We now turn to one example: the transition from sea to land.
The transition to land: sea creatures to land animals
Fossils of land animals, or tetrapods, first appear in rocks that are about 370 million years old. In older rocks, only sea creatures are found. But in 1998, scientists found a fossilized fin, 370 million years old, with eight digits similar to the five fingers humans have on their hands. However, the fin was undoubtedly that of a fish, which means this fossil is strong evidence of a transitional form.
One of the great success stories in the examination of the fossil record was the finding of a near-perfect fossilized transition between a vertebrate adapted for water and one adapted for land. Evolutionary biologist Neil Shubin set out to find a more complete transitional specimen than the 1998 fin. He determined the exact age of rock that he expected would yield a transitional land/water animal, and then he and his team spent four summers in the Arctic scouring rocks of that age to find one. The results were spectacular: they found a fish with gills and scales, but with a flattened head like a crocodile and strong fins that could support the animal’s weight in the shallows. Tiktaalik, as the specimen is named, is a remarkable example of the predictive power of evolutionary theory.
Fossils tell us about God
Sometimes the beauty and wonder of fossils get lost in arguments about evolution. When we step back, we can appreciate that every new fossil we find is a gift—a small piece of the vast, complex puzzle that is the history of life on our planet. For the Christian, fossils can help us reflect on the kind of world God has made.
Consider the mosasaurs, a group of ocean-dwelling reptiles. As long as a school bus, these fearsome predators ruled the sea for 20 million years. (To put that in perspective, Homo sapiens have only walked the earth for 200,000 years!)
What do the sheer number, diversity, and strangeness of extinct creatures like the mosasaurs, and the vast ages over which they lived, tell us about God and his world? First, they reveal that predation and extinction have been a reality for millions of years, long before humans. That means predation and extinction are not the result of the Fall, as some Christians believe, but part of God’s good world. This is consistent with the biblical description of a Creator who glories in the strength and ferocity of fearsome creatures (Job 38-41), but perhaps nuances our understanding about life and death.
Second, the long ages involved suggest that God takes time to create—lots of time. God is patient! The arrival of innumerable species over the ages means that Creation is not a “once and done” event; it is ongoing. These observations have implications for how we interpret the days of creation in Genesis 1.
Finally, we need to wrestle with the fact that the vast majority of the creatures God has made no longer walk the earth. They existed for a time, not for human enjoyment or use during their life, but solely for God’s good pleasure and purposes. God could have created in any way he wanted to, but he chose to do so in a particular way. Fossils—ancient, beautiful, and fascinating—give us clues about how. We have scientists to thank for their painstaking work that gives us a glimpse into these creatures’ lives.
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Image Credits: Sedimentary rocks by Wilson44691 (Public Domain); Tiktaalik by Eduard Solà (CC BY-SA 3.0); Tylosaur Bruce by Loozrboy from Toronto, Canada (CC BY-SA 2.0).