In this episode of the I Can't Sleep Podcast, fall asleep while learning about fossils. These relics give us a glimpse into what life was like millions of years ago. However, I can't remember much about what I read to tell you more. They're old... I guess that's all I've got this time. Happy sleeping!
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Transcript
Welcome to the I Can't Sleep Podcast, Where I read random articles from across the web to bore you to sleep with my soothing voice. I'm your host, Benjamin Boster. Today's episode is from a Wikipedia article titled, Fossil. A fossil, From classical Latin fossilis, Literally obtained by digging, Is any preserved remains, Impressions, Or trace of any once-living thing, From a past geological age. Examples include bones, Shells, Exoskeletons, Stone imprints of animals or microbes, Objects preserved in amber, Hair, Petrified wood, And DNA remnants. The totality of fossils is known as the fossil record. Geology is the study of fossils, Their age, Method of formation, And evolutionary significance. Specimens are usually considered to be fossils if they are over 10, 000 years old. The oldest fossils are around 3. 48 billion years to 4. 1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization, Including permineralization, Casts and molds, Pathogenic mineralization, Replacement and recrystallization, Adpression, Carbonization, And bioimmunization. Fossils vary in size from one micrometer bacteria to dinosaurs and trees, Many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, Usually that portion that was partially mineralized during life, Such as the bones and teeth of vertebrates or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, Such as animal tracks or feces. These types of fossil are called trace fossils, As opposed to body fossils. Some fossils are biochemical and are called chemifossils or biosignatures. Though the fossil record is incomplete, Numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth. In addition, The record can predict and fill gaps, Such as the discovery of Tiktaalik in the Arctic of Canada. The process of fossilization varies according to tissue type and external conditions. Permineralization is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism, Spaces filled with liquid or gas during life, Become filled with mineral-rich groundwater. Fossils precipitate from the groundwater, Occupying the empty spaces. This process can occur in very small spaces, Such as within the cell wall of a plant cell. Small-scale permineralization can produce very detailed fossils. For permineralization to occur, The organism must become covered by sediment soon after death. Otherwise the remains are destroyed by scavengers or decomposition. The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth. Other fossils contain traces of skin, Feathers, Or even soft tissues. This is a form of diagenesis. In some cases, The original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an external mold. If this void is later filled with sediment, The resulting cast resembles what the organism looked like. An endocast, Or internal mold, Is the result of sediments filling an organism's interior, Such as the inside of a bivalve or snail, Or the hollow of a skull. Endocasts are sometimes termed as steinkerns, Especially when bivalves are preserved this way. Othogenic mineralization is a special form of cast and mold formation. If the chemistry is right, The organism, Or fragment of organism, Can act as a nucleus for the precipitation of minerals, Such as siderite, Resulting in a nodule forming around it. If this happens rapidly before significant decay to the organic tissue, Very fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mason Creek fossil beds of Illinois are among the best documented examples of such mineralization. Replacement occurs when the shell, Bone, Or other tissue is replaced with another mineral. In some cases, Mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal compounds are still present, But in a different crystal form, As from aragonite to calcite. Compression fossils, Such as those of fossil ferns, Are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case, The fossil consists of original material, Albeit in a geochemically altered state. This chemical change is an expression of diagenesis. Often what remains is a carbonaceous film, Known as phytolyme, In which case the fossil is known as a compression. Often however, The phytolyme is lost and all that remains is an impression of the organism in the rock, An impression fossil. In many cases, However, Compressions and impressions occur together. For instance, When the rock is broken open, The phytolyme will often be attached to one part, Compression, Whereas the counterpart will just be an impression. For this reason, One term covers the two modes of preservation, Adpression. Because of their antiquity, An unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, Including blood vessels and the isolation of proteins and evidence for DNA fragments. In 2014, Mary Schweitzer and her colleagues reported the presence of iron particles associated with soft tissues recovered from dinosaur fossils. Based on various experiments that studied the interaction of iron and hemoglobin with blood vessel tissue, They proposed that solution hypoxia coupled with iron chelation enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues. However, A slightly older study based on eight taxa ranging in time from the Devonian to the Jurassic found that reasonably well-preserved fibrils that probably represent collagen were preserved in all these fossils and that the quality of preservation depended mostly on the arrangement of the collagen fibers, With tight packing favoring good preservation. There seemed to be no correlation between geological age and quality of preservation within that time frame. Fossils that are carbonized or coalified consist of the organic remains, Which have been reduced primarily to the chemical element carbon. Carbonized fossils consist of a thin film which forms a silhouette of the original organism, And the original organic remains were typically soft tissues. Coalified fossils consist primarily of coal, And the original organic remains were typically woody in composition. Bioimmoration occurs when a skeletal organism overgrows, Or otherwise subsumes another organism, Preserving the latter, Or an impression of it within the skeleton. Usually it is a sessile skeletal organism, Such as a bryozoan or an oyster, Which grows along a substrate, Covering other sessile sclerobins. Sometimes the bioimmured organism is soft-bodied, And is then preserved in negative relief as a kind of external mold. There are also cases where an organism settles on top of a living skeletal organism that grows upwards, Preserving the settler in its skeleton. Bioimmuration is known in the fossil record from the Ordovician to the recent. Organic fossils, Also known as guide fossils, Indicator fossils, Or zone fossils, Are fossils used to define and identify geologic periods, Or faunal stages. They work on the premise that, Although different sediments may look different depending on the conditions under which they were deposited, They may include the remains of the same species of fossil. The shorter the species time range, The more precisely different sediments can be correlated, And so rapidly evolving species fossils are particularly valuable. The best index fossils are common, Easy to identify at species level, And have a broad distribution, Otherwise the likelihood of finding and recognizing one in the two sediments is poor. Trace fossils consist mainly of tracks and burrows, But also include coprolites and marks left by feeding. Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilized hard parts, And they reflect animal behaviors. Many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Whilst exact assignment of trace fossils to their makers is generally impossible, Traces may for example provide the earliest physical evidence of the appearance of moderately complex animals. Coprolites are classified as trace fossils as opposed to body fossils as they give evidence for the animal's behavior, In this case diet, Rather than morphology. They were first described by William Buckland in 1829. Prior to this, They were known as fossil fur cones and basaur stones. They serve a valuable purpose in paleontology because they provide direct evidence of the predation and diet of extinct organisms. Coprolites may range in size from a few millimeters to over 60 centimeters. A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. Because of the incompleteness of the fossil record, There is usually no way to know exactly how close a transitional fossil is to the point of divergence. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Microfossil is a descriptive term applied to fossilized plants and animals whose size is just at or below the level at which the fossil can be analyzed by the naked eye. A commonly applied cutoff point between micro and macro fossils is one millimeter. Microfossils may either be complete or near-complete organisms in themselves or component parts of larger animals or plants. Microfossils are of critical importance as a reservoir of paleoclimate information and are also commonly used by biostratigraphers to assist in the correlation of rock units. Fossil resin, Colloquially called amber, Is a natural polymer found in many types of strata throughout the world, Even the Arctic. The oldest fossil resin dates to the Triassic, Though most dates to the Cenozoic. The excretion of the resin by certain plants is thought to be an evolutionary adaptation for protection from insects and to seal wounds. Fossil resin often contains other fossils called inclusions that were captured by the sticky resin. These include bacteria, Fungi, Other plants, And animals. Animal inclusions are usually small invertebrates, Predominantly arthropods such as insects and spiders, And only extremely rarely a vertebrate such as a small lizard. Preservation of inclusions can be exquisite, Including small fragments of DNA. A derived, Reworked, Or remanié fossil is a fossil found in rock that accumulated significantly later than when the fossilized animal or plant died. These fossils are created by erosion exhuming fossils from the rock formation in which they were originally deposited and their redeposition in a younger sedimentary deposit. Fossil wood is wood that is preserved in the fossil record. Wood is usually the part of a plant that is best preserved, And most easily found. Fossil wood may or may not be petrified. The fossil wood may be the only part of a plant that has been preserved, Therefore such wood may get a special kind of botanical name. This will usually include xylon and a term indicating its presumed affinity, Such as aracharioxylon, Wood of aracharia, Or some related genus. The term subfossil can be used to refer to remains such as bones, Nests, Or fecal deposits whose fossilization process is not complete, Either because the length of time since the animal involved was living is too short, Or because the conditions in which the remains were buried were not optimal for fossilization. Subfossils are often found in caves or other shelters where they can be preserved for thousands of years. The main importance of subfossil versus fossil remains is that the former contain organic material, Which can be used for radiocarbon dating, Or extraction and sequencing of DNA, Protein, Or other biomolecules. Additionally, Isotope ratios can provide much information about the ecological conditions under which extinct animals lived. Subfossils are useful for studying the evolutionary history of an environment and can be important to studies in paleoclimatology. Subfossils are often found in depositionary environments, Such as lake sediments, Oceanic sediments, And soils. Once deposited, Physical and chemical weathering can alter the state of preservation, And small subfossils can also be ingested by living organisms. Subfossils remains that date from the Mesozoic are exceptionally rare, Are usually in an advanced state of decay, And are consequently much disputed. The vast bulk of subfossil material comes from quaternary sediments, Including many subfossilized curonamid head capsules, Ostracod carapaces, Diadoms, And foraminifera. For remains such as mollusc and seashells, Which frequently do not change their chemical composition over geological time, And many occasionally even retain such features as the original color markings for millions of years, The label subfossil is applied to shells that are understood to be thousands of years old, But are of Holocene age, And therefore are not old enough to be from the Pleistocene epoch. Chemical fossils, Or chemifossils, Are chemicals found in rocks and fossil fuels, Petroleum, Coal, And natural gas, That provide an organic signature for ancient life. Molecular fossils and isotope ratios represent two types of chemical fossils. The oldest traces of life on Earth are fossils of this type, Including carbon-isotope anomalies found in zircons that imply the existence of life as early as 4. 1 billion years ago. Paleontology seeks to map out how life evolved across geological time. A substantial hurdle is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age, And can be accurate to within 0. 5% or better. Although radiometric dating requires careful laboratory work, Its basic principle is simple. The rates at which various radioactive elements decay are known, And so the ratio of the radioactive elements to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, And so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, Which may provide termini for the intervening sediments. Consequently, Paleontologists rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the layer cake that is the sedimentary record. Rocks normally form relatively horizontal layers, With each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, The fossil's ages claim to lie between the two known ages. Because rock sequences are not continuous, But may be broken up by faults or periods of erosion, It is very difficult to match up rock beds that are not directly adjacent. However, Fossils of species that survive for a relatively short time can be used to match isolated rocks. This technique is called biostratigraphy. If rocks of unknown age have traces of E. Pseudoplanus, They have a mid-Ordovician age. Such index fossils must be distinctive, Be globally distributed, And occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating, A was before B, Which is often sufficient for studying evolution. However, This is difficult for some time periods because of the problems involved in matching rocks of the same age across continents. Family tree relationships also help to narrow down the date when lineages first appeared. For instance, If fossils of B or C date to X million years ago, And the calculated family tree says A was an ancestor of B and C, Then A must have evolved earlier. It is also possible to estimate how long ago two living clades diverged. In other words, Approximately how long ago their last common ancestor must have lived, By assuming that DNA mutations accumulate at a constant rate. These molecular clocks, However, Are fallible, And provide only approximate timing. For example, They are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, And estimates produced by different techniques may vary by a factor of two. Fossils are only rarely preserved as fossils in the best of circumstances, And only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, Suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, Only a small percentage of life forms can be expected to be represented in discoveries, And each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, Which will never demonstrate an exact halfway point. The fossil record is strongly biased toward organisms with hard parts, Leaving most groups of soft-bodied organisms with little to no role. It is replete with mollusks, The vertebrates, The echinoderms, The brachiopods, And some groups of arthropods. Fossil sites with exceptional preservation, Sometimes including preserved soft tissues, Are known as Lagerstätten, German for storage places. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, Thus slowing decomposition. Lagerstätten span geological time from the Cambrian period to the present. Worldwide, Some of the best examples of near-perfect fossilization are the Cambrian Maotian shales and Burgess shale, The Devonian Hunsrich slates, The Jurassic Solnhofen limestone, And the Carboniferous Mason Creek localities. Stromatolites are layered accretionary structures formed in shallow water by the trapping, Binding, And cementation of sedimentary grains by biofilms of microorganisms, Especially cyanobacteria. Stromatolites provide some of the most ancient fossil records of life on Earth, Dating back more than 3. 5 billion years ago. Stromatolites were much more abundant in pre-Cambrian times, While older Archean fossil remains are presumed to be colonies of cyanobacteria, Younger, That is protozoic, Fossils, Maybe primordial forms of the eukaryote chlorophytes, That is, Green algae. One genus of stromatolite very common in the geological record is Cholonea. The earliest stromatolite of confirmed microbial origin dates to 2. 724 billion years ago. A 2009 discovery provides strong evidence of microbial stromatolites extending as far back as 3. 45 billion years ago. Stromatolites are a major constituent of the fossil record for life's first 3. 5 billion years, Peaking about 1. 25 billion years ago. They subsequently declined in abundance and diversity, Which by the start of the Cambrian had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victims to grazing creatures, The Cambrian substrate revolution, Implying that sufficiently complex organisms were common over 1 billion years ago. The connection between grazer and stromatolite abundance is well documented in the younger Ordovician evolutionary radiation. Stromatolite abundance also increased after the end-Ordovician and end-Permian extinctions decimated marine animals. Fluctuations in metazoan population and diversity may not have been the only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes. While prokaryotic cyanobacteria themselves reproduced at a much higher rate than stromatolites, The number of stromatolites was much smaller. May have been responsible for changes. While prokaryotic cyanobacteria themselves reproduced asexually through cell division, They were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria are thought to be largely responsible for increasing the amount of oxygen in the primeval Earth's atmosphere through their continuing photosynthesis. Cyanobacteria use water, Carbon dioxide, And sunlight to create their food. A layer of mucus often forms over mats of cyanobacterial cells. In modern microbial mats, Debris from the surrounding habitat can become trapped within the mucus, Which can be cemented by the calcium carbonate to grow thin laminations of limestone. These laminations can accrete over time, Resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight, The organisms for photosynthesis. Layered spherical growth structures, Termed oncolites, Are similar to the stromatolites and are also known from the fossil record. Ocolites are poorly laminated or non-laminated clotted structures formed by a cyanobacteria common in the fossil record and in modern sediments. The Zebra River Canyon area of the Cubis platform in the deeply dissected Zarus Mountains of southwestern Namibia provides an extremely well-exposed example of the thrombolyte stromatolite metazoan reefs that developed during the Proterozoic period, The stromolites here being better developed in up-dip locations under conditions of higher current velocities and greater sediment influx.
4.9 (35)
Carol
June 22, 2024
Who’d have thought….well I didn’t get to the end , but the first 10 minutes were interesting. 😂
Sandy
June 18, 2024
I was reminded of a college course years ago that I nearly failed because the professor's voice would put me to sleep. I hope there isn't a test, because I didn't study. I slept.
Beth
June 17, 2024
I’d comment on how it was but I was asleep in 5 minutes, must have been pretty dull! 😂😂😂 Thank you!
