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Simple harmonic motion
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In mechanics and physics, simple harmonic motion is a special type of periodic motion or oscillation motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement.
Simple harmonic motion can serve as a mathematical model for a variety of motions, such as the oscillation of a spring. In addition, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum as well as molecular vibration. Simple harmonic motion is typified by the motion of a mass on a spring when it is subject to the linear elastic restoring force given by Hooke's Law. The motion is sinusoidal in time and demonstrates a single resonant frequency. For simple harmonic motion to be an accurate model for a pendulum, the net force on the object at the end of the pendulum must be proportional to the displacement. This is a good approximation when the angle of the swing is small.
Simple harmonic motion provides a basis for the characterization of more complicated motions through the techniques of Fourier analysis. Therefore it can be simply defined as the periodic motion of a body along a straight line, such that the acceleration is directed towards the center of the motion and also proportional to the displacement from that point.
Contents
[hide]
1 Introduction
2 Dynamics
3 Energy
4 Examples
4.1 Mass on a spring
4.2 Uniform circular motion
4.3 Mass of a simple pendulum
4.4 Scotch yoke
5 See also
6 Notes
7 References
8 External links
Introduction[edit]
The motion of a particle moving along a straight line with an acceleration which is always towards a fixed point on the line and whose magnitude is proportional to the distance from the fixed point is called simple harmonic motion [SHM].[citation needed]
Simple harmonic motion shown both in real space and phase space. The orbit is periodic. (Here the velocity and position axes have been reversed from the standard convention to align the two diagrams)
In the diagram, a simple harmonic oscillator, consisting of a weight attached to one end of a spring, is shown. The other end of the spring is connected to a rigid support such as a wall. If the system is left at rest at the equilibrium position then there is no net force acting on the mass. However, if the mass is displaced from the equilibrium position, the spring exerts a restoring elastic force that obeys Hooke's law.
Mathematically, the restoring force F is given by
F = − k x , {\displaystyle \mathbf {F} =-k\mathbf {x} ,}
where F is the restoring elastic force exerted by the spring (in SI units: N), k is the spring constant (N·m−1), and x is the displacement from the equilibrium position (m).
For any simple mechanical harmonic oscillator:
When the system is displaced from its equilibrium position, a restoring force that obeys Hooke's law tends to restore the system to equilibrium.
Once the mass is displaced from its equilibrium position, it experiences a net restoring force. As a result, it accelerates and starts going back to the equilibrium position. When the mass moves closer to the equilibrium position, the restoring force decreases. At the equilibrium position, the net restoring force vanishes. However, at x = 0, the mass has momentum because of the acceleration that the restoring force has imparted. Therefore, the mass continues past the equilibrium position, compressing the spring. A net restoring force then slows it down until its velocity reaches zero, whereupon it is accelerated back to the equilibrium position again.
As long as the system has no energy loss, the mass continues to oscillate. Thus simple harmonic motion is a type of periodic motion.
Dynamics[edit]
In Newtonian mechanics, for one-dimensional simple harmonic motion, the equation of motion, which is a second-order linear ordinary differential equation with constant coefficients, can be obtained by means of Newton's second law and Hooke's law for a mass on a spring.
F n e t = m d 2 x d t 2 = − k x , {\displaystyle F_{\mathrm {net} }=m{\frac {\mathrm {d} ^{2}x}{\mathrm {d} t^{2}}}=-kx,}
where m is the inertial mass of the oscillating body, x is its displacement from the equilibrium (or mean) position, and k is a constant (the spring constant for a mass on a spring). (Note that in reality this is in fact an approximation, only valid for speeds that are small compared to the speed of light.)
Therefore,
d 2 x d t 2 = − k m x , {\displaystyle {\frac {\mathrm {d} ^{2}x}{\mathrm {d} t^{2}}}=-{\frac {k}{m}}x,}
Solving the differential equation above produces a solution that is a sinusoidal function.
x ( t ) = c 1 cos  ( ω t ) + c 2 sin  ( ω t ) {\displaystyle x(t)=c_{1}\cos \left(\omega t\right)+c_{2}\sin \left(\omega t\right)}
This equation can be written in the form:
x ( t ) = A cos  ( ω t − φ ) , {\displaystyle x(t)=A\cos \left(\omega t-\varphi \right),}
where
ω = k m , A = c 1 2 + c 2 2 , tan  φ = c 2 c 1 , {\displaystyle \omega ={\sqrt {\frac {k}{m}}},\qquad A={\sqrt {{c_{1}}^{2}+{c_{2}}^{2}}},\qquad \tan \varphi ={\frac {c_{2}}{c_{1}}},}
In the solution, c1 and c2 are two constants determined by the initial conditions, and the origin is set to be the equilibrium position.[A] Each of these constants carries a physical meaning of the motion: A is the amplitude (maximum displacement from the equilibrium position), ω = 2πf is the angular frequency, and φ is the phase.[B]
Using the techniques of calculus, the velocity and acceleration as a function of time can be found:
v ( t ) = d x d t = − A ω sin  ( ω t − φ ) , {\displaystyle v(t)={\frac {\mathrm {d} x}{\mathrm {d} t}}=-A\omega \sin(\omega t-\varphi ),}
Speed:
ω A 2 − x 2 {\displaystyle {\omega }{\sqrt {A^{2}-x^{2}}}}
Maximum speed: ωA (at equilibrium point)
a ( t ) = d 2 x d t 2 = − A ω 2 cos  ( ω t − φ ) . {\displaystyle a(t)={\frac {\mathrm {d} ^{2}x}{\mathrm {d} t^{2}}}=-A\omega ^{2}\cos(\omega t-\varphi ).}
Maximum acceleration: Aω2 (at extreme points)
By definition, if a mass m is under SHM its acceleration is directly proportional to displacement.
a ( x ) = − ω 2 x . {\displaystyle a(x)=-\omega ^{2}x.}
where
ω 2 = k m {\displaystyle \omega ^{2}={\frac {k}{m}}}
Since ω = 2πf,
f = 1 2 π k m , {\displaystyle f={\frac {1}{2\pi }}{\sqrt {\frac {k}{m}}},}
and, since T = 1/f where T is the time period,
T = 2 π m k . {\displaystyle T=2\pi {\sqrt {\frac {m}{k}}}.}
These equations demonstrate that the simple harmonic motion is isochronous (the period and frequency are independent of the amplitude and the initial phase of the motion).
Energy[edit]
Substituting ω2 with k/m, the kinetic energy K of the system at time t is
K ( t ) = 1 2 m v 2 ( t ) = 1 2 m ω 2 A 2 sin 2  ( ω t + φ ) = 1 2 k A 2 sin 2  ( ω t + φ ) , {\displaystyle K(t)={\tfrac {1}{2}}mv^{2}(t)={\tfrac {1}{2}}m\omega ^{2}A^{2}\sin ^{2}(\omega t+\varphi )={\tfrac {1}{2}}kA^{2}\sin ^{2}(\omega t+\varphi ),}
and the potential energy is
U ( t ) = 1 2 k x 2 ( t ) = 1 2 k A 2 cos 2  ( ω t + φ ) . {\displaystyle U(t)={\tfrac {1}{2}}kx^{2}(t)={\tfrac {1}{2}}kA^{2}\cos ^{2}(\omega t+\varphi ).}
In the absence of friction and other energy loss, the total mechanical energy has a constant value
E = K + U = 1 2 k A 2 . {\displaystyle E=K+U={\tfrac {1}{2}}kA^{2}.}
Examples[edit]
An undamped spring–mass system undergoes simple harmonic motion.
The following physical systems are some examples of simple harmonic oscillator.
Mass on a spring[edit]
A mass m attached to a spring of spring constant k exhibits simple harmonic motion in closed space. The equation for describing the period
T = 2 π m k {\displaystyle T=2\pi {\sqrt {\frac {m}{k}}}}
shows the period of oscillation is independent of both the amplitude and gravitational acceleration. The above equation is also valid in the case when an additional constant force is being applied on the mass, i.e. the additional constant force cannot change the period of oscillation.
Uniform circular motion[edit]
Simple harmonic motion can be considered the one-dimensional projection of uniform circular motion. If an object moves with angular speed ω around a circle of radius r centered at the origin of the xy-plane, then its motion along each coordinate is simple harmonic motion with amplitude r and angular frequency ω.
Mass of a simple pendulum[edit]
The motion of an undamped pendulum approximates to simple harmonic motion if the angle of oscillation is small.
In the small-angle approximation, the motion of a simple pendulum is approximated by simple harmonic motion. The period of a mass attached to a pendulum of length l with gravitational acceleration g {\displaystyle g} is given by
T = 2 π l g {\displaystyle T=2\pi {\sqrt {\frac {l}{g}}}}
This shows that the period of oscillation is independent of the amplitude and mass of the pendulum but not of the acceleration due to gravity, g {\displaystyle g} , therefore a pendulum of the same length on the Moon would swing more slowly due to the Moon's lower gravitational field strength. Because the value of g {\displaystyle g} varies slightly over the surface of the earth, the time period will vary slightly from place to place and will also vary with height above sea level.
This approximation is accurate only for small angles because of the expression for angular acceleration α being proportional to the sine of the displacement angle:
− m g l sin  θ = I α , {\displaystyle -mgl\sin \theta =I\alpha ,}
where I is the moment of inertia. When θ is small, sin θ ≈ θ and therefore the expression becomes
− m g l θ = I α {\displaystyle -mgl\theta =I\alpha }
which makes angular acceleration directly proportional to θ, satisfying the definition of simple harmonic motion.
Scotch yoke[edit]
Main article: Scotch yoke
A Scotch yoke mechanism can be used to convert between rotational motion and linear reciprocating motion. The linear motion can take various forms depending on the shape of the slot, but the basic yoke with a constant rotation speed produces a linear motion that is simple harmonic in form.
See also[edit]
Newtonian mechanics
Small-angle approximation
Rayleigh–Lorentz pendulum
Isochronous
Uniform circular motion
Complex harmonic motion
Damping
Harmonic oscillator
Pendulum (mathematics)
Circle group
String vibration
Notes[edit]
^ The choice of using a cosine in this equation is arbitrary. Other valid formulations are:
x ( t ) = A sin  ( ω t + φ ′ ) , {\displaystyle x(t)=A\sin \left(\omega t+\varphi '\right),}
where
tan  φ ′ = c 1 c 2 , {\displaystyle \tan \varphi '={\frac {c_{1}}{c_{2}}},}
since cos θ = sin(π/2 − θ).
^ The maximum displacement (that is, the amplitude), xmax, occurs when cos(ωt ± φ) = 1, and thus when xmax = A.
References[edit]
Walker, Jearl (2011). Principles of Physics (9th ed.). Hoboken, N.J. : Wiley. ISBN 0-470-56158-0.
Thornton, Stephen T.; Marion, Jerry B. (2003). Classical Dynamics of Particles and Systems (5th ed.). Brooks Cole. ISBN 0-534-40896-6.
John R Taylor (2005). Classical Mechanics. University Science Books. ISBN 1-891389-22-X.
Grant R. Fowles; George L. Cassiday (2005). Analytical Mechanics (7th ed.). Thomson Brooks/Cole. ISBN 0-534-49492-7.
External links[edit]
Simple Harmonic Motion from HyperPhysics
Java simulation of spring-mass oscillator
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text:
Devonian
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about the geological period. For the residents of the English county, see Devon.
Devonian Period
419.2–358.9 million years ago
PreЄ
Є
O
S
D
C
P
T
J
K
Pg
N
Mean atmospheric O
2 content over period duration c. 15 vol %[1][2]
(75 % of modern level
Mean atmospheric CO
2 content over period duration c. 2200 ppm[3]
(8 times pre-industrial level)
Mean surface temperature over period duration c. 20 °C[4]
(6 °C above modern level)
Sea level (above present day) Relatively steady around 189m, gradually falling to 120m through period[5]
Events of the Devonian Period
view • discuss • edit
-420 —
–
-415 —
–
-410 —
–
-405 —
–
-400 —
–
-395 —
–
-390 —
–
-385 —
–
-380 —
–
-375 —
–
-370 —
–
-365 —
–
-360 —
–
-355 —
Silurian
Lochkovian
Pragian
Emsian
Eifelian
Givetian
Frasnian
Famennian
Carbon-
iferous
←
Rhynie chert[6]
←
Hangenberg event
←
Kellwasser event(s)[7]
←
Widespread[8]
shrubs & trees
←
S. America
glaciation begins
←
Hunsrück fauna
D
e
v
o
n
i
a
n
Palæozoic
Key events of the Devonian Period.
Axis scale: millions of years ago.
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya.[9] It is named after Devon, England, where rocks from this period were first studied.
The first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established.
Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the "Age of Fish". The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating almost every known aquatic environment. The ancestors of all four-limbed vertebrates (tetrapods) began adapting to walking on land, as their strong pectoral and pelvic fins gradually evolved into legs.[10] In the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician.
The first ammonites, species of molluscs, appeared. Trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction which started about 375 million years ago[11] severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida.
The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, and the early formation of the small continent of Euramerica in between.
Contents
[hide]
1 History
2 Subdivisions
3 Climate
4 Paleogeography
5 Life
5.1 Marine biota
5.2 Reefs
5.3 Terrestrial biota
5.3.1 The greening of land
5.3.2 Animals and the first soils
6 Late Devonian extinction
7 See also
8 References
9 External links
History[edit]
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Also see: Human timeline and Nature timeline
The rocks of Lummaton Quarry in Torquay in Devon played an early role in defining the Devonian period.
The period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was eventually resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough. Murchison and Sedgwick won the debate and named the period they proposed as the Devonian System.[12][13][14]
While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy (Ogg, 2004), the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya (in North America, the beginning of the Mississippian subperiod of the Carboniferous).[9]
In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes",[15] referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian and Farlovian stages, the latter three of which are placed in the Devonian.[16]
The Devonian has also erroneously been characterized as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed greatly during its epochs and between geographic regions. For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, Australia, North America, and China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common.[citation needed]
Subdivisions[edit]
The Devonian Period is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System.
Early Devonian
The Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, and was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago.[citation needed]
Middle Devonian
The Middle Devonian comprised two subdivisions: first the Eifelian, which then gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments partly due to drastic environmental changes and partly due to the increasing competition, predation and diversity of jawed fishes. The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, and the ability to crawl out of the water and onto the land for short periods of time.[citation needed]
Late Devonian
Finally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivision, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, 358.9± 2.5 million years ago.[citation needed]
Climate[edit]
The Devonian was a relatively warm period, and probably lacked any glaciers. The temperature gradient from the equator to the poles was not as large as it is today. The weather was also very arid, mostly along the equator where it was the driest.[17] Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian.[17] CO2 levels dropped steeply throughout the Devonian period as the burial of the newly evolved forests drew carbon out of the atmosphere into sediments; this may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F).[17] The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to a Late Devonian warming.[17] The climate would have affected the dominant organisms in reefs; microbes would have been the main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids.
Paleogeography[edit]
The Paleo-Tethys Ocean opened during the Devonian
The Devonian period was a time of great tectonic activity, as Euramerica and Gondwana drew closer together.
The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the Hadley cell and the Ferrel cell. In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidized iron (hematite) characteristic of drought conditions.[18]
Near the equator, the plate of Euramerica and Gondwana were starting to meet, beginning the early stages of the assembling of Pangaea. This activity further raised the northern Appalachian Mountains and formed the Caledonian Mountains in Great Britain and Scandinavia.
The west coast of Devonian North America, by contrast, was a passive margin with deep silty embayments, river deltas and estuaries, found today in Idaho and Nevada; an approaching volcanic island arc reached the steep slope of the continental shelf in Late Devonian times and began to uplift deep water deposits, a collision that was the prelude to the mountain-building episode at the beginning of the Carboniferous called the Antler orogeny.[19]
Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical reef organisms lived. The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet. Other minor oceans were the Paleo-Tethys Ocean, Proto-Tethys Ocean, Rheic Ocean, and Ural Ocean (which was closed during the collision with Siberia and Baltica).
Life[edit]
Marine biota[edit]
Spindle diagram for the evolution of fish and other vertebrate classes. The diagram is based on Michael Benton, 2005.[20]
See also: Evolution of fish § Devonian: Age of fishes
Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederellids, microconchids and corals. Lily-like crinoids (animals, their resemblance to flowers notwithstanding) were abundant, and trilobites were still fairly common. Among vertebrates, jaw-less armored fish (ostracoderms) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both the sea and fresh water. Armored placoderms were numerous during the lower stages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous (Chondrichthyes) and bony fishes (Osteichthyes) also become diverse and played a large role within the Devonian seas. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. The great diversity of fish around at the time has led to the Devonian being given the name "The Age of Fish" in popular culture.
The first ammonites also appeared during or slightly before the early Devonian Period around 400 Mya.[21]
Reefs[edit]
A now dry barrier reef, located in present-day Kimberley Basin of northwest Australia, once extended a thousand kilometers, fringing a Devonian continent. Reefs in general are built by various carbonate-secreting organisms that have the ability to erect wave-resistant frameworks close to sea level. The main contributors of the Devonian reefs were unlike modern reefs, which are constructed mainly by corals and calcareous algae. They were composed of calcareous algae and coral-like stromatoporoids, and tabulate and rugose corals, in that order of importance.[clarification needed]
Dunkleosteus, one of the largest armoured fish ever to roam the planet, lived during the late Devonian
Early shark Cladoselache, several lobe-finned fishes, including Eusthenopteron that was an early marine tetrapod, and the placoderm Bothriolepis in a painting from 1905
Enrolled phacopid trilobite from the Devonian of Ohio
The common tabulate coral Aulopora from the Middle Devonian of Ohio – view of colony encrusting a brachiopod valve
Tropidoleptus carinatus, an orthid brachiopod from the Middle Devonian of New York.
Pleurodictyum americanum, Kashong Shale, Middle Devonian of New York
SEM image of a hederelloid from the Devonian of Michigan (largest tube diameter is 0.75 mm)
Devonian spiriferid brachiopod from Ohio which served as a host substrate for a colony of hederelloids
Terrestrial biota[edit]
By the Devonian Period, life was well underway in its colonization of the land. The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils and harbored arthropods like mites, scorpions, trigonotarbids[22] and myriapods (although arthropods appeared on land much earlier than in the Early Devonian[23] and the existence of fossils such as Climactichnites suggest that land arthropods may have appeared as early as the Cambrian). Also the first possible fossils of insects appeared around 416 Mya in the Early Devonian. Evidence for the earliest tetrapods takes the form of trace fossils in shallow lagoon environments within a marine carbonate platform/shelf during the Middle Devonian[24], although these traces have been questioned and an interpretation as fish feeding traces (Piscichnus) has been advanced.[25]

The greening of land[edit]
The Devonian period marks the beginning of extensive land colonization by plants. With large land-dwelling herbivores not yet present, large forests grew and shaped the landscape.
Many Early Devonian plants did not have true roots or leaves like extant plants and vascular tissue has yet to be observed in many of those plants. Some of the early land plants such as Drepanophycus likely spread by vegetative growth and primitive spores.[26] The earliest land plants such as Cooksonia consisted of leafless, dichotomous axes and terminal sporangia and were generally very short-statured, and grew hardly more than a few centimeters tall.[27] By far the largest land organism during this period was the enigmatic Prototaxites, which was possibly the fruiting body of an enormous fungus,[28] rolled liverwort mat,[29] or another organism of uncertain affinities[30] that stood more than 8 meters tall, and towered over the low, carpet-like vegetation. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms had evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest known trees, from the genus Wattieza, appeared in the Late Devonian around 385 Mya.[31] In the Late Devonian, the tree-like ancestral Progymnosperm Archaeopteris which had conifer-like true wood and fern-like foliage and the cladoxylopsids grew.[32] (See also: lignin.) These are the oldest known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion".
The 'greening' of the continents acted as a carbon sink, and atmospheric levels of carbon dioxide may have dropped. This may have cooled the climate and led to a massive extinction event. See Late Devonian extinction.
Animals and the first soils[edit]
Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterized a recognizably modern world had its genesis in the Late Devonian period. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. The rapid evolution of a terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek out a terrestrial living. By the end of the Devonian, arthropods were solidly established on the land.[33]
Late Devonian extinction[edit]
Main article: Late Devonian extinction
The Late Devonian is characterised by three episodes of extinction ("Late D")
A major extinction occurred at the beginning of the last phase of the Devonian period, the Famennian faunal stage (the Frasnian-Famennian boundary), about 372.2 Mya, when all the fossil agnathan fishes, save for the psammosteid heterostraci, suddenly disappeared. A second strong pulse closed the Devonian period. The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota, and was more drastic than the familiar extinction event that closed the Cretaceous.
The Devonian extinction crisis primarily affected the marine community, and selectively affected shallow warm-water organisms rather than cool-water organisms. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef-systems.
Amongst the severely affected marine groups were the brachiopods, trilobites, ammonites, conodonts, and acritarchs, as well as jawless fish, and all placoderms. Land plants as well as freshwater species, such as our tetrapod ancestors, were relatively unaffected by the Late Devonian extinction event (but see [34] for a counterargument that the Devonian extinctions nearly wiped out the tetrapods).
The reasons for the Late Devonian extinctions are still unknown, and all explanations remain speculative.[35] Canadian paleontologist Digby McLaren suggested in 1969 that the Devonian extinction events were caused by an asteroid impact. However, while there were Late Devonian collision events (see the Alamo bolide impact), little evidence supports the existence of a large enough Devonian crater.
See also[edit]
Category:Devonian plants
Falls of the Ohio State Park USA, Indiana. One of the largest exposed Devonian fossil beds in the world.
Geologic time scale
List of Early Devonian land plants
List of fossil sites (with link directory)
Phacops rana: a Devonian trilobite.
References[edit]
Jump up ^ Image:Sauerstoffgehalt-1000mj.svg
Jump up ^ File:OxygenLevel-1000ma.svg
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Jump up ^ Haq, B. U.; Schutter, SR (2008). "A Chronology of Paleozoic Sea-Level Changes". Science. 322 (5898): 64–68. Bibcode:2008Sci...322...64H. doi:10.1126/science.1161648. PMID 18832639.
Jump up ^ Parry, S. F.; Noble, S. R.; Crowley, Q. G.; Wellman, C. H. (2011). "A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications". Journal of the Geological Society. London: Geological Society. 168 (4): 863–872. doi:10.1144/0016-76492010-043.
Jump up ^ Kaufmann, B.; Trapp, E.; Mezger, K. (2004). "The numerical age of the Upper Frasnian (Upper Devonian) Kellwasser horizons: A new U-Pb zircon date from Steinbruch Schmidt(Kellerwald, Germany)". The Journal of Geology. 112 (4): 495–501. Bibcode:2004JG....112..495K. doi:10.1086/421077.
Jump up ^ Algeo, T. J. (1998). "Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events". Philosophical Transactions of the Royal Society B: Biological Sciences. 353 (1365): 113–130. doi:10.1098/rstb.1998.0195.
^ Jump up to: a b Gradstein, Felix M.; Ogg, J. G.; Smith, A. G. (2004). A Geologic Time Scale 2004. Cambridge: Cambridge University Press. ISBN 0521786738.
Jump up ^ Amos, Jonathan. "Fossil tracks record 'oldest land-walkers'". news.bbc.co.uk. BBC News. Retrieved 24 December 2016.
Jump up ^ Newitz, Annalee. "How Do You Have a Mass Extinction Without an Increase in Extinctions?". The Atlantic.
Jump up ^ Rudwick M.S.J. 1985 The great Devonian controversy: the shaping of scientific knowledge among gentlemanly specialists. Chicago: University of Chicago Press.
Jump up ^ Note:
Sedgwick and Murchison coined the term "Devonian system" in: Adam Sedgwick and Roderick Impey Murchison (1840) "On the physical structure of Devonshire, and on the subdivisions and geological relations of its older stratified deposits, etc.," Transactions of the Geological Society of London, 2nd series, 5 (part II) : 633-687 (Part I) and 688-705 (Part II). From p. 701: "We propose therefore, for the future, to designate these groups collectively by the name Devonian system, … ."
Sedgwick and Murchison acknowledged William Lonsdale's role in proposing, on the basis of fossil evidence, the existence of a Devonian stratum between those of the Silurian and Carboniferous periods. From (Sedgwick and Murchison, 1840), p. 690: "Again, Mr. Lonsdale, after an extensive examination of the fossils of South Devon, had pronounced them, more than a year since, to form a group intermediate between those of the Carboniferous and Silurian systems, … ."
William Lonsdale stated that in December 1837 he had suggested the existence of a stratum between the Silurian and Carboniferous ones. See: William Lonsdale (1840) "Notes on the age of limestones from south Devonshire," Transactions of the Geological Society of London, 2nd series, 5 (part II) : 721-738 ; see especially pp. 724 and 727. From p. 724: " … Mr. Austen's communication [was] read December 1837, … . It was immediately after the reading of that paper … that I formed the opinion relative to the limestones of Devonshire being of the age of the old red sandstone; and which I afterwards suggested first to Mr. Murchison and then to Prof. Sedgwick, … ."
Jump up ^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. Cambridge University Press. ISBN 9780521786737.
Jump up ^ Age of Fishes Museum
Jump up ^ Barclay, W.J. 1989. Geology of the South Wales Coalfield Pt II, the country around Abergavenny, 3rd edn. Memoir of the British Geological Survey Sheet 232 (Eng & Wales) pp18-19
^ Jump up to: a b c d Joachimski, M. M.; Breisig, S.; Buggisch, W. F.; Talent, J. A.; Mawson, R.; Gereke, M.; Morrow, J. R.; Day, J.; Weddige, K. (2009). "Devonian climate and reef evolution: Insights from oxygen isotopes in apatite". Earth and Planetary Science Letters. 284 (3–4): 599–609. Bibcode:2009E&PSL.284..599J. doi:10.1016/j.epsl.2009.05.028. - Graph of palaeotemperature from Conodont apatite
Jump up ^ "Devonian Period | geochronology". Encyclopedia Britannica. Retrieved 2017-12-15.
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Jump up ^ Benton, M. J. (2005) Vertebrate Palaeontology John Wiley, 3rd edition, page 14. ISBN 9781405144490.
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Jump up ^ Garwood, Russell J.; Dunlop, Jason (July 2014). "The walking dead: Blender as a tool for paleontologists with a case study on extinct arachnids". Journal of Paleontology. Paleontological Society. 88 (4): 735–746. doi:10.1666/13-088. ISSN 0022-3360. Retrieved 2015-07-21.
Jump up ^ Garwood, Russell J.; Edgecombe, Gregory D. (September 2011). "Early Terrestrial Animals, Evolution, and Uncertainty". Evolution: Education and Outreach. New York: Springer Science+Business Media. 4 (3): 489–501. doi:10.1007/s12052-011-0357-y. ISSN 1936-6426. Retrieved 2015-07-21.
Jump up ^ Niedźwiedzki (2010). "Tetrapod trackways from the early Middle Devonian period of Poland". Nature. 463 (7277): 43–48. Bibcode:2010Natur.463...43N. doi:10.1038/nature08623. PMID 20054388.
Jump up ^ Lucas (2015). "Thinopus and a Critical Review of Devonian Tetrapod Footprints". Ichnos. 22 (3–4): 136–154. doi:10.1080/10420940.2015.1063491.
Jump up ^ Zhang, Ying-ying; Xue, Jin-Zhuang; Liu, Le; Wang, De-ming (2016). "Periodicity of reproductive growth in lycopsids: An example from the Upper Devonian of Zhejiang Province, China". Paleoworld. 25 (1): 12–20. doi:10.1016/j.palwor.2015.07.002.
Jump up ^ Gonez, Paul; Gerrienne, Philippe (2010). "A new definition and a lectotypification of the genus Cooksonia Lang 1937". International Journal of Plant Sciences. 171 (2): 199–215. doi:10.1086/648988.
Jump up ^ Hueber, Francis M. (2001). "Rotted wood-alga fungus: The history and life of Prototaxites Dawson 1859". Review of Palaeobotany and Palynology. 116: 123–159. doi:10.1016/s0034-6667(01)00058-6.
Jump up ^ Graham, Linda E.; Cook, Martha E; Hanson, David T.; Pigg, Kathleen B.; Graham, James M. (2010). "Rolled liverwort mats explain major Prototaxites features: Response to commentaries". American Journal of Botany. 97 (7): 1079–1086. doi:10.3732/ajb.1000172. PMID 21616860.
Jump up ^ Taylor, Thomas N.; Taylor, Edith L.; Decombeix, Anne-Laure; Schwendemann, Andrew; Serbet, Rudolph; Escapa, Ignacio; Krings, Michael (2010). "The enigmatic Devonian fossil Prototaxites is not a rolled-up liverwort mat: Comment on the paper by Graham et al.(AJB 97: 268–275)". American Journal of Botany. 97 (7): 1074–1078. doi:10.3732/ajb.1000047. PMID 21616859.
Jump up ^ Smith, Lewis (April 19, 2007). "Fossil from a forest that gave Earth its breath of fresh air". The Times. London. Retrieved May 1, 2010.
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Jump up ^ Gess, R.W. (2013). "The earliest record of terrestrial animals in Gondwana: A scorpion from the Famennian (Late Devonian) Witpoort Formation of South Africa". African Invertebrates. 54 (2): 373–379. doi:10.5733/afin.054.0206.
Jump up ^ McGhee, George R. (2013). When the Invasion of Land Failed. New York: Columbia University Press.
Jump up ^ Citation needed
General
Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) https://web.archive.org/web/20060716071827/http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
Palaeos
Age of Fishes Museum
External links[edit]
Wikisource has original works on the topic: Paleozoic#Devonian
Wikimedia Commons has media related to Devonian.
The Devonian times - an excellent and frequently updated resource focussing on the Devonian period
UC Berkeley site introduces the Devonian.
"International Commission on Stratigraphy (ICS)". Geologic Time Scale 2004. Retrieved September 19, 2005.
Examples of Devonian Fossils
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Late Devonian

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Middle Devonian

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Early Devonian

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Late Ordovician

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Middle Ordovician

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values:
https://af.wikipedia.org/wiki/Devoon
Devoon – Afrikaans
af
af
interlanguage-link-target

values:
interlanguage-link interwiki-af
display: none;

values:
interlanguage-link interwiki-als
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values: عصر ديفوني – Arabic

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interlanguage-link interwiki-ast
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values: ডেভোনিয়ান – Bangla

values:
interlanguage-link interwiki-bn
display: none;

values:
https://bjn.wikipedia.org/wiki/Devonian
Devonian – Banjar
bjn
bjn
interlanguage-link-target

values:
interlanguage-link interwiki-bjn
display: none;

values:
interlanguage-link interwiki-zh-min-nan
display: none;

values: Девон осоро – Bashkir

values:
interlanguage-link interwiki-ba
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values: Дэвонскі перыяд – Belarusian

values:
interlanguage-link interwiki-be
display: none;

values: Дэвонскі пэрыяд – Belarusian (Taraškievica orthography)

values:
interlanguage-link interwiki-be-x-old
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values:
interlanguage-link interwiki-bg
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values:
https://br.wikipedia.org/wiki/Devonian
Devonian – Breton
br
br
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interlanguage-link interwiki-br
display: none;

values:
interlanguage-link interwiki-ca
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values:
https://cy.wikipedia.org/wiki/Defonaidd
Defonaidd – Welsh
cy
cy
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interlanguage-link interwiki-da
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https://et.wikipedia.org/wiki/Devon
Devon – Estonian
et
et
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values:
interlanguage-link interwiki-et
display: none;

values: Δεβόνια περίοδος – Greek

values:
interlanguage-link interwiki-el
display: none;

values: interlanguage-link interwiki-es badge-Q17437798 badge-goodarticle

values:
https://eo.wikipedia.org/wiki/Devonio
Devonio – Esperanto
eo
eo
interlanguage-link-target

values:
interlanguage-link interwiki-eo
display: none;

values:
https://eu.wikipedia.org/wiki/Devoniar
Devoniar – Basque
eu
eu
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interlanguage-link interwiki-eu
display: none;

values: دوونین – Persian

values:
interlanguage-link interwiki-fa
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values: Դևոնի ժամանակաշրջան – Armenian

values: डिवोनी कल्प – Hindi

values:
interlanguage-link interwiki-hr
display: none;

values:
https://it.wikipedia.org/wiki/Devoniano
Devoniano – Italian
it
it
interlanguage-link-target

values:
interlanguage-link interwiki-it
display: none;

values:
interlanguage-link interwiki-he
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values: დევონური სისტემა – Georgian

values:
interlanguage-link interwiki-ka
display: none;

values: Девон кезеңі – Kazakh

values: Девон мезгили – Kyrgyz

values:
https://la.wikipedia.org/wiki/Devonium
Devonium – Latin
la
la
interlanguage-link-target

values:
interlanguage-link interwiki-la
display: none;

values:
https://lv.wikipedia.org/wiki/Devons
Devons – Latvian
lv
lv
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values:
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display: none;

values:
interlanguage-link interwiki-lb
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values:
https://lt.wikipedia.org/wiki/Devonas
Devonas – Lithuanian
lt
lt
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values:
interlanguage-link interwiki-lt
display: none;

values:
https://li.wikipedia.org/wiki/Devoan
Devoan – Limburgish
li
li
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display: none;

values:
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interlanguage-link interwiki-ml
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interlanguage-link interwiki-mzn
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values:
https://ms.wikipedia.org/wiki/Devon
Devon – Malay
ms
ms
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values:
https://cdo.wikipedia.org/wiki/Devonian
Devonian – Min Dong Chinese
cdo
cdo
interlanguage-link-target

values:
interlanguage-link interwiki-cdo
display: none;

values:
https://nl.wikipedia.org/wiki/Devoon
Devoon – Dutch
nl
nl
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values:
interlanguage-link interwiki-nl
display: none;

values:
interlanguage-link interwiki-ja
display: none;

values:
interlanguage-link interwiki-no
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values:
https://nn.wikipedia.org/wiki/Devontida
Devontida – Norwegian Nynorsk
nn
nn
interlanguage-link-target

values:
interlanguage-link interwiki-nn
display: none;

values:
https://oc.wikipedia.org/wiki/Devonian
Devonian – Occitan
oc
oc
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interlanguage-link interwiki-oc
display: none;

values:
interlanguage-link interwiki-uz
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https://pms.wikipedia.org/wiki/Devonian
Devonian – Piedmontese
pms
pms
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display: none;

values:
interlanguage-link interwiki-nds
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values:
https://pl.wikipedia.org/wiki/Dewon
Dewon – Polish
pl
pl
interlanguage-link-target

values:
interlanguage-link interwiki-pl
display: none;

values:
https://pt.wikipedia.org/wiki/Devoniano
Devoniano – Portuguese
pt
pt
interlanguage-link-target

values:
https://ro.wikipedia.org/wiki/Devonian
Devonian – Romanian
ro
ro
interlanguage-link-target

values:
interlanguage-link interwiki-ro
display: none;

values: Девонский период – Russian

values:
https://sco.wikipedia.org/wiki/Devonian
Devonian – Scots
sco
sco
interlanguage-link-target

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interlanguage-link interwiki-sco
display: none;

values:
interlanguage-link interwiki-simple
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values:
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values: Девон (периода) – Serbian

values:
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values: டெவோனியக் காலம் – Tamil

values: ยุคดีโวเนียน – Thai

values:
interlanguage-link interwiki-th
display: none;

values:
https://tr.wikipedia.org/wiki/Devoniyen
Devoniyen – Turkish
tr
tr
interlanguage-link-target

values:
interlanguage-link interwiki-tr
display: none;

values: Девонський період – Ukrainian

values:
interlanguage-link interwiki-uk
display: none;

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interlanguage-link interwiki-vi
display: none;

values:
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display: none;

values: All languages (initial selection from common choices by you and others)

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