Dating rocks with fossils i c p dating game

The major groups of organisms that we are familiar with evolved between the late Proterozoic and the Cambrian (~600 Ma to ~520 Ma).

Plants, which evolved in the oceans as green algae, came onto land during the Ordovician (~450 Ma).

Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.

To determine the ages of these specimens, scientists need an isotope with a very long half-life.

Fossils alone cannot provide us with numerical ages of rocks, but over the past century geologists have acquired enough isotopic dates from rocks associated with fossil-bearing rocks (such as igneous dykes cutting through sedimentary layers) to be able to put specific time limits on most fossils.

A very selective history of life on Earth over the past 600 million years is provided in Figure 8.3.1.

Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.

In the past 150 years they have not found any fossils that Darwin would not have expected.New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of the great ‘tree of life’.Darwin and his contemporaries could never have imagined the improvements in resolution of stratigraphy that have come since 1859, nor guessed what fossils were to be found in the southern continents, nor predicted the huge increase in the number of amateur and professional paleontologists worldwide.Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites).These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils.Like extant organisms, fossils vary in size from microscopic, even single bacterial cells one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons.

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