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Tree remains that have undergone petrifaction, as seen in Petrified Forest National Park. In geology, petrifaction or petrification (from Ancient Greek πέτρα (pétra) 'rock, stone') is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals.
The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology , biostratigraphy and superposition were the only means for determining the relative age of rocks.
Fossils are direct evidence of life. In the search for the earliest life, fossils are often supplemented by geochemical evidence. The fossil record does not extend as far back as the geochemical record due to metamorphic processes that erase fossils from geologic units.
This is because inclusions can act like "fossils" – trapping and preserving these early melts before they are modified by later igneous processes. In addition, because they are trapped at high pressures many melt inclusions also provide important information about the contents of volatile elements (such as H 2 O, CO 2 , S and Cl) that drive ...
Fossils of organisms' bodies are usually the most informative type of evidence. The most common types are wood, bones, and shells. [57] Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time.
Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria, common in the fossil record and in modern sediments. [18] There is evidence that thrombolites form in preference to stromatolites when foraminifera are part of the biological community. [36]
Such an intermediate form should have many fish-like characteristics, conserved from 385 million years ago or more, but also have many amphibian characteristics as well. In 2004, an expedition to islands in the Canadian arctic searching specifically for this fossil form in rocks that were 375 million years old discovered fossils of Tiktaalik. [132]
The trackway Protichnites from the Cambrian, Blackberry Hill, central Wisconsin. A trace fossil, also known as an ichnofossil (/ ˈ ɪ k n oʊ f ɒ s ɪ l /; from Greek: ἴχνος ikhnos "trace, track"), is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself. [1]