How reliable is fossil evidence?

Answer 1

The answer depends on how the word 'reliable' is interpreted in the question:

(1) Is the fossil evidence 'reliable' in interpreting the history of life on Earth?

Fossil evidence IS our understanding of the history of life. Fossils on which this understanding is based include skeletons, roots, leaves, bark, chemical signatures, imprints, carbon residues, burrowing and trail marks, petrified wood, footprints, eggs, gastric stones, fecal matter, and many others, found preserved mainly in stone, but sometimes in ice. There are many ways that fossils can be formed. They include freezing, carbonization, petrification, mineral replacement, unaltered preservation,

recrystallization, andauthigenicpreservation.

The fossil record of life recorded in rock is full of periods of intense diversification, appearances of new lifeforms, and extinction events that affected large percentages of the biota on a worldwide scale.

(2) Are the modern methods used to determine the age of the fossil 'reliable'?Radiometric dating of rock involves the measurement of the amount of decay in radioactive elements which are present in the rock. Radioactive elements decay at unique rates, depending on the isotope. This rate of decay is known as half-lives; it is the time necessary for ½ of the atoms to decay in a particular element. The decay follows a geometric scale, in that in the first half-life of an element, ½ of the atoms decay, yet in the second half-life, ½ of those remaining decay and so forth. By measuring this decay, and knowing the half life of an element, scientists can date a sample. Radiometric dating is particularly useful in dating igneous and metamorphic rock, but not so much for sedimentary rocks and fossils.

Because of geologic events such as plate tectonics and volcanism, suitable material for radiometric dating, such as volcanic tuff, solidified lava, and igneous intrusions have been found as layers on, in, and cut through layers of sedimentary rock and fossils. Intrusions are always younger than the rock body they penetrate, meaning that the sedimentary rock in which intrusions are found will be older than a radiometrically dated sample of the intrusion. Lava flows and volcanic ash which form layers in rock will be younger than the rock below and older than the rock above. The solidified intrusions and lava flows can be dated with radiometric techniques.

The radiometric dating of suitable rocks (i.e. igneous or metamorphic) in proximity to their sedimentary counterparts, therefore allows the sedimentary rock to be dated as well. Radiometric dating techniques are constantly being refined and improved with a resulting increase in accuracy and date range.

Scientific inquiry and the scientific method have contributed greatly to our lives in the fields of electronics, physics, engineering, chemistry, manufacturing, and medicine. This same scientific method is being used in genetics and Earth Sciences to broaden our knowledge and understanding of Earth's history, including the origin and evolution of life.

Answer 2

Carbon dating can give an educated guess of the age of carbon tested and then be cross referenced with other fossil records. This is accepted by most, but not all, to be reliable.