Paleogeograpiya

Ang Paleogeography, na-spell din na palaeogeography, ang sinaunang heograpiya ng ibabaw ng Earth. Ang heograpiya ng Daigdig ay patuloy na nagbabago: ang mga kontinente ay lumilipat bilang isang resulta ng mga pakikipag-ugnay sa plate na tectonic; ang mga saklaw ng bundok ay tumataas at sumabog; at ang mga antas ng dagat ay tumataas at nahuhulog habang nagbabago ang dami ng mga basins ng karagatan. Ang mga pagbabagong ito sa heograpiya ay maaaring masubaybayan sa pamamagitan ng pag-aaral ng rekord ng rock at fossil, at ang data ay maaaring magamit upang lumikha ng paleogeographic na mga mapa, na naglalarawan kung paano lumipat ang mga kontinente at kung paano ang mga nakaraan na lokasyon ng mga bundok, kapatagan, mababaw na dagat, at malalim na karagatan ng karagatan. nagbago.

Ang pag-aaral ng paleogeography ay may dalawang pangunahing layunin. Ang una ay i-mapa ang mga nakaraang posisyon ng mga kontinente at mga basins ng karagatan, at ang pangalawa ay upang ilarawan ang nagbabago na mga tampok na heograpiya ng Earth sa pamamagitan ng oras.

Pagma-map sa mga nakaraang kontinente at karagatan

Ang mga nakaraang posisyon ng mga kontinente ay maaaring matukoy sa pamamagitan ng paggamit ng anim na pangunahing linya ng katibayan: paleomagnetism, linear magnetic anomalies, hot-spot track, paleobiogeography, paleoclimatology, at geologic at tectonic history.

Paleomagnetism

Sa pamamagitan ng pagsukat ng natitirang magnetic field na madalas na napreserba sa mga bato na naglalaman ng mga mineral na nagdadala ng bakal, ang pagtatasa ng paleomagnetic ay maaaring matukoy kung ang isang bato ay na-magnetized malapit sa isa sa mga pole ng Earth o malapit sa Equator. Ang mga mineral na nagdadala ng bakal na bumubuo sa nakangiting bato ay nakahanay sa kanilang sarili sa magnetic field ng Earth habang pinapalamig ang tinunaw na bato. Ang mga mineral na ito ay nakahanay sa kanilang mga sarili kapag sila ay nadeposito sa mga sediment, at pinapanatili nila ang kanilang oryentasyon habang nilalagay sila sa sedimentary rock. Ang mga linya ng puwersa sa magnetic field ng Earth ay kahanay sa ibabaw ng planeta sa Equator at patayo sa mga poste. Samakatuwid, ang mga mineral na nagdadala ng bakal na nabuo o idineposito sa mababang mga latitude ay halos kahanay sa ibabaw ng Earth, habang ang mga nasa mataas na latitude ay malubog na matunaw. Kung ang mga bato ay kalaunan ay dinadala ng mga proseso ng tektonik,ang kanilang orihinal na latitude ng pag-aalis ay maaaring matukoy ng kanilang oryentasyon. Ang Paleomagnetism ay nagbibigay ng direktang katibayan ng nakaraan ng hilaga-timog (latitudinal) na posisyon ng isang kontinente, ngunit hindi nito pinipigilan ang posisyon sa silangan-paayon (paayon).

Linear magnetic anomalies

Earth’s magnetic field has another important property. Like the Sun’s magnetic field, Earth’s magnetic field periodically “flips,” or reverses polarity—that is, the North and South poles switch places. Fluctuations, or anomalies in the intensity of the magnetic field, occur at the boundaries between normally magnetized sea floor and sea floor magnetized in the reversed direction. The age of these magnetic anomalies can be established by using fossil evidence and radiometric age determinations. Because these magnetic anomalies form at oceanic ridges, they tend to be long, linear features (hence the name linear magnetic anomalies) that are symmetrically disposed about ridge axes. The past positions of the continents during the last 150 million years (the maximum age of most of the ocean floor) can be directly reconstructed by superimposing linear magnetic anomalies of the same age, in effect “undoing” the results of sea-floor spreading since that time.

Hot-spot tracks

Some of the world’s volcanoes are formed by jets of molten rock that arise at the boundary between Earth’s core and mantle (at a depth of about 2,900 km, or 1,800 miles). These rising plumes, or hot spots, puncture the lithosphere, and, as a tectonic plate moves across the hot spot, a line of islands is generated. The island directly above the hot spot is the youngest, and islands become progressively older with distance from the hot spot. There are more than a dozen well-documented hot-spot tracks. Perhaps the most obvious is the Hawaiian Islands, which trace an east-west arc across the central Pacific Ocean. Hot-spot tracks accurately record plate motions and can be used to determine the past latitudinal and longitudinal position of the continents.

Paleobiogeography

The past distribution of plants and animals can give important clues about the latitudinal position of the continents as well as their relative positions. Cold-water faunas can often be distinguished from warm-water faunas, and ancient floras reflect both paleotemperature and paleorainfall. The diversity of plants and animals tends to increase toward the Equator, and the adaptations of plants (such as smooth-edged leaves in the tropics and serrated-edged leaves in the temperate belts) are often good indicators of the amount of ancient rainfall.

The similarity or dissimilarity of faunas and floras on different continents can also be used to estimate their geographic proximity. In addition, the evolutionary history of groups of plants and animals on different continents can reveal when these continents were connected or isolated from each other. For example, Australia’s unique marsupial fauna is the result of its isolation from the other continents at the time when placental mammals were evolving on the other continents during the early Paleogene Period.

Paleoclimatology

Earth’s climate is primarily a result of the redistribution of the Sun’s energy across the surface of the globe. It is warm near the Equator and cool near the poles. Wetness or rainfall also varies systematically from the Equator to the pole in alternating bands. It is wet near the Equator, dry in the subtropics, wet in the temperate belts, and dry near the poles. Certain kinds of rocks form under specific climatic conditions. For example, coals occur where wet climates once supported lush vegetation; bauxite (the principal ore of aluminum) is formed in warm and wet conditions, evaporites and calcretes require warmth and aridity to form; and tillites are deposited during the movement of glacial ice. The ancient distribution of these and other rock types can indicate how the global climate has changed through time and how the continents have traveled across the climatic belts.

Geologic and tectonic history

In order to reconstruct the past positions of the continents, it is necessary to understand the evolution of plate tectonic boundaries. Only by understanding the regional geologic and tectonic history of an area can the location and timing of rifting events, subduction activity, continental collision, and other major plate tectonic events be determined.