Category Science

Why is the ocean salty?

You could be out in the middle of the ocean – surrounded by thousands of kilometres of water – and not have any water to drink when you’re thirsty. Why? Because ocean water is full of salt. If you did drink it, it would simply make you more thirsty.

The ocean is salty because rivers dump salt into it. All the rivers that flow down mountainsides and over the land tear loose tonnes of minerals. Most of these minerals are different kinds of salts. The rivers carry these salts to the ocean.

There’s never enough salt in most rivers to make the river water taste salty. But rivers have been dumping salt into the ocean for millions of years. By now, there is enough salt in the ocean to cover all of the land on the earth with a layer of salt hundreds of metres deep!

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How we can classify land on the earth?

Land on the Earth

The earth is a huge ball, but it is not smooth all over like a ball that you bounce or roll. The earth’s surface is full of bumps and dips, but some parts of it are smooth. Where there’s no water, there is land.

Some of the earth’s surface is on the ocean floor. You live on one of the earth’s continents – or maybe on an island. You may live on a mountain, in a valley, on a plain, or in a desert.

Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughout history has occurred in land areas that support agriculture, habitat, and various natural resources. Some life forms, including terrestrial plants and terrestrial animals, have developed from predecessor species that originated in bodies of water.

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What is referred to as the Cambrian explosion which took place nearly 541million years ago?

The Cambrian explosion or Cambrian radiation was an event approximately 541 million years ago in the Cambrian period when practically all major animal phyla started appearing in the fossil record. It lasted for about 13 – 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversifications in other groups of organisms as well.

The rapid appearance of a wide variety of animals – particularly bilaterians – led to the development of radical new ecological interactions such as predation. Consequently, ecosystems became much more complex than those of the Ediacaran. As the number and variety of organisms increased, they occupied a variety of new marine environments and habitats. Cambrian seas teemed with animals of various sizes, shapes, and ecologies; some lived on or in the sea floor (a benthic lifestyle), while others actively swam in the water column (nektonic).

The fundamental ecological structure of modern marine communities was firmly established during the Cambrian. By the end of the Period, some animals had also made the first temporary forays onto land, soon to be followed by plants.

 

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What is the Devonian period named after?

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. 

A fossil creature from the Devonian discovered more recently has been hailed as a vital link between fish and the first vertebrates to walk on land. Found in the Canadian Arctic in 2004, Tiktaalik had a crocodile-like head and strong, bony fins that scientists think it used like legs to move in shallow waters or even on land. The fish showed other characteristics of terrestrial animals, including ribs, a neck, and nostrils on its snout for breathing air.

Plants began spreading beyond the wetlands during the Devonian, with new types developing that could survive on dry land. Toward the end of the Devonian the first forests arose as stemmed plants evolved strong, woody structures capable of supporting raised branches and leaves. Some Devonian trees are known to have grown 100 feet (30 meters) tall. By the end of the period the first ferns, horsetails, and seed plants had also appeared.

 

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What is biostratigraphy used for?

Biostratigraphy is the branch of stratigraphy that uses fossils to establish relative ages of rock and correlate successions of sedimentary rocks within and between depositional basins. A biozone is an interval of geologic strata characterised by certain fossil taxa. Such intervals are often defined by the first appearances (range bases), apparent extinctions (range tops/last appearances), or abundances of fossil index species. These key index species should be relatively abundant, short-lived taxa that are easy to recognise and as geographically widespread as possible. Widely used fossil groups include brachiopods, conodonts, dinoflagellate cysts, foraminifera, graptolites, nannofossil, spores and pollen and trilobites. Zonal schemes based on several different fossil groups can be used in parallel, and the zones can be calibrated to the absolute geological timescale using tie points to rocks which have been radio-isotopically dated.

There are several kinds of biostratigraphy. Formal biostratigraphy is concerned with the delineation of biostratigraphic zones, which are bodies of rock defined by the presence of selected nominal taxa (fossil species or groups whose name is attached to the biostratigraphic zone). A special kind of formal biostratigraphy is called biochronostratigraphy, which requires nominal taxa that are short-lived and thus their existence defines well a short interval of geological time. Informal biostratigraphy is concerned with using fossil taxa to help define ancient environments, a type of study called paleoecology (the study of ancient ecology preserved in sedimentary rocks).

 

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What are ammonites?

Ammonites, which evolved about 416 million years ago, were once the most abundant animals of the ancient seas. These sea creatures first appeared 415 million years ago in the form of a small, straight shelled creature, known as Bacrites. They quickly evolved into a variety of shapes and sizes including some shaped like hairpins. During their evolution the ammonites faced no less than three catastrophic events that would eventually lead to their extinction. The first event occurred during the Permian (250 million years ago), where only 10% survived. These surviving species went on to flourish throughout the Triassic, however at the end of this period (206 million years ago) they faced near extinction, when all but one species survived. This event marked the end of the Triassic and the beginning of the Jurassic, during which time the number of ammonite species grew once more. The final catastrophe occurred at the end of the Cretaceous period when all species were annihilated and the ammonites became extinct. This event apparently coincided with the death of the dinosaurs.

Based on the fossil record, ammonites came in a wide range of sizes and shapes, from smaller than an inch to as large as nine feet wide. Some ammonites had long, straight shells, while others had helix-shaped shells. Most species, however, had coiled shells lined with progressively larger chambers separated by thin walls called septa.

The many chambers of their shells likely helped these cephalopods glide through the planet’s warm, shallow seas. A thin, tubelike structure called a siphuncle pumped air through the interior chambers of the shell, which scientists believe helped provide buoyancy and move ammonites through the water. It’s unclear whether ammonites were very efficient swimmers, though.

Scientists believed that ammonites, like modern cephalopods, had soft body tissue with tentacles attached to their heads for catching prey. Fossil evidence indicates they had sharp, beaklike jaws to snare prey such as plankton, crustaceans, and other ammonites. They were also preyed on by larger reptiles and fish.

 

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