Human Errors finishes by turning to the brain. Lents is keen not to cause offence. He reassures us, as he does throughout, that the brain is remarkable perhaps for fear of creating a cohort of hypochondriacs among his readers. Nevertheless, like everything else, it too is littered with flaws. Having analysed the way our brain plays tricks on us, warping memories, falling for optical illusions and encouraging reckless behaviour, Lents finally turns to the most dangerous human trait of all — superior intelligence.
Of course, our intelligence has allowed us to solve many human problems with technology, rather than relying on the clumsy march of evolution.
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Alfred A. This timescale is not divided up into eras based on the strict passage of time, but on the disappearance or appearance of species. In a glass-partitioned room beside the museum, a white-capped and gowned technician, Andrew Grebneff, works carefully to expose a bone by removing surrounding rock under a magnifier using a miniature air tool. Science, optics, and music in medieval and early modern thought. The eLife model is intended to counter traditional journals, which some scientists criticize as too slow and expensive.
Try our in-depth dossiers that provide a comprehensive view of each topic Hung out to dry. Mexico City: boom town. When the wind blows. Natural Capital: Putting a price on nature. Alien views. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy. For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period.
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. However, this is difficult for some time periods, because of the problems involved in matching rocks of the same age across continents. 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. Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point.
The fossil record is strongly biased toward organisms with hard-parts, leaving most groups of soft-bodied organisms with little to no role. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. 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 were much more abundant in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria , younger that is, Proterozoic fossils may be primordial forms of the eukaryote chlorophytes that is, green algae.
One genus of stromatolite very common in the geologic record is Collenia. The earliest stromatolite of confirmed microbial origin dates to 2. A discovery provides strong evidence of microbial stromatolites extending as far back as 3. Stromatolites are a major constituent of the fossil record for life's first 3.
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, falling back to earlier levels as marine animals recovered.
Factors such as the chemistry of the environment may have been responsible for changes. While prokaryotic cyanobacteria themselves reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria as well as extremophile Gammaproteobacteria 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 to the organisms for photosynthesis.
Layered spherical growth structures termed oncolites are similar to stromatolites and are also known from the fossil record.
Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria common in the fossil record and in modern sediments. The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of southwestern Namibia provides an extremely well exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx.
Index 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 fossil feces and marks left by feeding. Many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour in this case, diet rather than morphology.
They were first described by William Buckland in Prior to this they were known as "fossil fir cones " and " bezoar stones. 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.
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.
Microfossils may either be complete or near-complete organisms in themselves such as the marine plankters foraminifera and coccolithophores or component parts such as small teeth or spores 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.
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 the 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 Araucarioxylon wood of Araucaria or some related genus , Palmoxylon wood of an indeterminate palm , or Castanoxylon wood of an indeterminate chinkapin. The term subfossil can be used to refer to remains, such as bones, nests, or defecations, whose fossilization process is not complete, either because the length of time since the animal involved was living is too short less than 10, years 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.
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.