So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.
Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.
Find additional lessons, activities, videos, and articles that focus on relative and absolute dating.
(The use of the phrase to describe the new fossil has ignited debate between creationists and evolutionists, though the discovery says nothing about man's relationship to apes.) more generically.
Sometimes the phrase implies that a fossil is the direct ancestor of two or more extant species. Most fossils represent species that are morphologically similar to a predicted ancestor but not connected in a straight line to any modern species.
—to describe an abrupt transition in the types of fossils he found in adjacent layers of sediment.
In 1863, a Scottish physician named John Crawfurd uttered the phrase for the first time as a critique of evolution: He demanded the missing fossil evidence to show "how a monkey became a man." in 1924 answered Crawfurd's charge, his use of the phrase to describe a common undiscovered ancestor of human and nonhuman primates captured the popular imagination and still hasn't let go.
Scientists sometimes substitute the phrase for the more technical-sounding "transitional morphologies," which refers to anatomical structures that bear some resemblance to both older and more recent physiology.
But the research community tends to frown on the use of such language, and the discoverers of Ida have been criticized in some quarters for overselling their research.According to media reports, the discovery is a missing link in human evolution.The research team itself is pushing the same idea: They've just released a book about the fossil called —news stories have used it to describe no fewer than 28 paleontological discoveries in the past decade.By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as "bracketing" the age of the sedimentary layer in which the fossils occur.Teach your students about absolute dating: Determining age of rocks and fossils, a classroom activity for grades 9-12.That means that in 5730 years, half of the C14 will decay to nitrogen 14.