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Across 1. which states that only living organisms can produce other living organisms. 6. a basic law of geochronology, stating that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it. 8. subdivision of an era on the geological time scale. 12. is model that express the major geological and biological events in earths history. 14. the science of the forms of life existing in former geologic periods, as represented by their fossils.

Down 2. theory attempts to explain the origins of organelles such as mitochondria and chloroplasts in eukaryotic cells. 3. the now discredited theory that living organisms can arise spontaneously from inanimate matter; spontaneous generation. 4. The rapid diversification of multicellular animal life around the beginning of the Cambrian Period, resulting in the appearance of almost all modern animal phyla. 5. a major division of geologic time composed of a number of periods. 7. any method of determining the age of earth materials or objects of organic origin based on measurement of either short-lived radioactive elements or the amount of a long-lived radioactive element plus its decay product. 8. a theory of global tectonics in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates. 9. layer of iridium-rich material between rocks of the cretaceous period and rocks of the paleogene period that provides evidence of a meteorite impact. 10. in archaeology, the arrangement of artifacts or events in a sequence relative to one another but without ties calendrically measured time; the arrangement of artifacts in a typological sequence or seriation 11. the constant time period required for the disintegration of half of the atoms in a sample of some specific radioactive substance 13. any remains, impression, or trace of a living thing of a former geologic age, as a skeleton, footprint