Fossils and Evolution

Introduction

One of the best lines of evidence for organic evolution is the changes in plants, animals, and other organisms through geologic time as recorded in the fossil record. Fossils found in national park areas tell important parts of the story of life on the North American continent from the Precambrian (Mesoproterozoic) (1,450 million years ago) through the Holocene (the last 11,700 years). Taken together, fossils in parks present a compelling account of organic evolution, from stromatolite (algal mounds) fossils in Glacier National Park in Montana to Pleistocene mammoth fossils in Tule Springs National Monument in Nevada. Older rock layers contain fossils of simpler organisms and younger rock layers contain those of more complex and more modern lifeforms.

Paleontology is among the scientific disciplines that demonstrate that evolution, through natural selection in response to factors such as extinction events and the varying environmental conditions that provide a range of habitats for living things, is responsible for the diversity of life of Earth.

The history of life as recorded in the fossil record is complemented by information from the fields of genetics and molecular biology, anatomy, and biogeography to provide a robust validation of the theory of evolution.

Differences in what fossils are present in geologic strata of different ages is evident both within individual parks and in the rock record as a whole preserved throughout the National Park System.

Grand Canyon National Park serves as an excellent example of changing life through time in a single place. It contains fossils in sedimentary bedrock that range in age from about 1,255 million years old to about 220 million years old, plus Late Pleistocene and Holocene fossils found in caves.

Faunal Succession

The principle of faunal succession is essential in understanding the fossil record through geologic time as recorded in sedimentary strata. This general law states that fossil organisms succeed one another in a definite and recognizable order through geologic time as recorded in the rock record. Each geologic formation has a different record of life from what is found in the formations above it and below it. The principle of faunal succession also allows determination of the relative age of rocks using their fossil content.

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