My Science School

People have been catching fish from the sea, rivers and lakes for thousands of years. Fishing is still a source of food, and an important industry for many people living near the sea. Japan, China and Russia are the largest commercial fishing nations. The world's major fishing grounds are the areas of relatively shallow waters that lie above the continental shelf - those parts of the Earth's landmasses that are submerged by ocean waters.

Most sea fish are caught by fishermen working on trawlers. Trawlers are equipped with a large net that is trawled (dragged) along the sea bed. Distant-water trawlers, the most numerous type, can stay at sea for several months. Many of them have freezers so the fish can be gutted and frozen on board. Middle-water trawlers go out for two or three weeks and near-water trawlers for only a few days at a time.

Trawlers catch demersal fish, those kinds that live near the sea bed. North Atlantic trawlers catch cod in the cold waters off Canada, Greenland and Scandinavia. Japanese and American fleets catch tuna in the deep waters of the Pacific Ocean.

Middle-water trawlers catch fish such as halibut and plaice, while near-water vessels catch fish that live in the warmer waters close to shore, such as haddock, plaice, sole and turbot. These boats do not have freezers on board but the fish can be packed in ice to keep them fresh.

Different techniques are used to catch other marine creatures. Lobsters and crabs are caught in small traps called pots. Oysters and scallops are collected with a dredge, a triangular steel frame with a net on it, which is towed along by a fishing boat.

Today, in many traditional fishing grounds numbers of fish are declining fast, the result of overfishing. In the North Atlantic, herring are now almost extinct and there are far fewer cod and haddock. The use of huge factory ships, on which large quantities of fish can be frozen, is severely depleting supplies for local people in developing countries, who rely on fish for their livelihood. There is also concern about the destruction of ocean food chains by overfishing. It is estimated that 20 million tonnes of fish a year are discarded by fishing boats because they are not the right kind - a practice that needlessly reduces stocks of other kinds of fish.

TRADITIONAL FISHING

In some parts of the world, fishermen still go out in small boats and catch fish with hand-held nets, as they have done for centuries. These fishermen catch only enough fish for their local communities.

Whales used to be hunted for their meat and oil. Harpoons and factory ships were used. So many species became endangered that commercial whaling of a number of different species was banned by international agreement in 1986.

Picture Credit : Google

At about the same time as people began to grow crops, they also domesticated wild animals for meat, milk and skins or wool. This was the start of livestock farming.

Cattle are kept for milk and meat. There are about 200 million cattle in India alone, with about 1000 million in the rest of the world. Breeds of cattle can be divided into two main groups: the European breeds, which are descended from a now-extinct species of long-horned wild cattle called the auroch, and the various breeds of zebu, the humped cattle of India.

Animals kept for their wool include sheep, goats, rabbits, and vicunas (a type of llama). Of these, sheep are the most common on farms worldwide. Australia is one of the world's biggest wool producers. Of the 1000 million sheep in the world, about 140 million are in Australia where, in fact, there are many more sheep than people! Australian farmers keep large herds of sheep on huge sheep stations. Most of the sheep are Merinos, a breed that has soft; thick wool and which can survive on the poor grass that is characteristic of the dry grasslands of central Australia.

Some livestock farmers keep pigs for meat. On large modern pig farms, the animals are kept indoors in controlled conditions and fed a mixture which makes them put on the most weight in the shortest time. About 400 breeds of pig have been produced over the centuries but many of these have now disappeared with the development of intensive farming methods. The main surviving breeds include the Berkshire, Chester White, Poland, China, Saddleback, Yorkshire, Duroc, and Razorback. There are about 800 million pigs in the world, half of them in Asia. Their meat is sold as pork (fresh meat), bacon or ham (cured or preserved meat).

POULTRY

Poultry farmers keep chickens, turkeys, geese and other birds for meat and eggs. Chickens are descended from tropical forest birds found in Southeast Asia. They can be reared by intensive or free-range methods. There are about 7000 million chickens in the world. Good breeds for egg-laying include Leghorns and Minorcas. Dorking and Cornish breeds are good for meat, and Orpingtons and Rhode Island Reds are useful for both. Turkeys, ducks and geese are mainly reared for their meat.

Deep deposits are reached by driving a shaft vertically into the ground. Miners descend the shaft in a lift. An air shaft takes fresh air down into the mine, where poisonous gases may accumulate. Trucks carry the mined material to a freight lift, which brings them to the surface. Trucks may also be used to take miners to the nearest deposits. Drift mines are dug where the deposit lies in an outcrop of rock near the surface. The seam can be mined directly from the surface, which is often on the slope of a hill.

Deep deposits are reached by driving a shaft vertically into the ground. Miners descend the shaft in a lift. An air shaft takes fresh air down into the mine, where poisonous gases may accumulate. Trucks carry the mined material to a freight lift, which brings them to the surface. Trucks may also be used to take miners to the nearest deposits. Drift mines are dug where the deposit lies in an outcrop of rock near the surface. The seam can be mined directly from the surface, which is often on the slope of a hill.

There are underground mines all over the world presenting a kaleidoscope of methods and equipment. There are approximately 650 underground mines, each with an annual output that exceeds 150,000 tonnes, which account for 90% of the ore output of the western world. In addition, it is estimated that there are 6,000 smaller mines each producing less than 150,000 tonnes. Each mine is unique with workplace, installations and underground workings dictated by the kinds of minerals being sought and the location and geological formations, as well as by such economic considerations as the market for the particular mineral and the availability of funds for investment. Some mines have been in continuous operation for more than a century while others are just starting up.

Mines are dangerous places where most of the jobs involve arduous labour. The hazards faced by the workers range from such catastrophes as cave-ins, explosions and fire to accidents, dust exposure, noise, heat and more. Protecting the health and safety of the workers is a major consideration in properly conducted mining operations and, in most countries, is required by laws and regulations.

The underground mine is a factory located in the bedrock inside the earth in which miners work to recover minerals hidden in the rock mass. They drill, charge and blast to access and recover the ore, i.e., rock containing a mix of minerals of which at least one can be processed into a product that can be sold at a profit. The ore is taken to the surface to be refined into a high-grade concentrate.

Working inside the rock mass deep below the surface requires special infrastructures: a network of shafts, tunnels and chambers connecting with the surface and allowing movement of workers, machines and rock within the mine. The shaft is the access to underground where lateral drifts connect the shaft station with production stops. The internal ramp is an inclined drift which links underground levels at different elevations (i.e., depths). All underground openings need services such as exhaust ventilation and fresh air, electric power, water and compressed air drains and pumps to collect seeping ground water, and a communication system.

Opencast mines are used when the deposit lies near the surface. Overlying earth and rock can be moved by machine or washed away with water. Although opencast mining is cheaper than digging deep mines, some people feel that the environmental costs of it are high, as large areas of land are laid bare and wildlife destroyed. Nowadays great attention is often paid to landscaping the area after an opencast mine has been abandoned. Many are made into parks or wildlife refuges. Planting the areas also helps to stabilize heaps of spoil.

Opencast mining operation involves generation of massive mine waste, altering the existing landscapes, alterations to drainage patterns etc. As a result, significant areas of land are degraded and existing ecosystems are replaced by undesirable wastes. To mitigate the impact on environment, a structured and adoptable environment management practice is being continuously developed at NLCIL. Eco-friendly mining can be broadly brought up under conservation of natural resources, prevention and regulation of polluting activities and action plans for eco regeneration.

Opencast mining operations involve huge quantities of overburden removal, dumping and backfilling in excavated areas. A substantial increase in the rate of accumulation of waste dumps in recent years has resulted in greater height of the dump for minimum ground cover area and also given rise to danger of dump failures. Further, steeper open-pit slopes are prone to failure. These failures lead to loss of valuable human life and damage to mining machinery. There is a need for continuous monitoring of dump and pit slopes, as well as for providing early warning before the occurrence of slope failure. Different technologies have been developed for slope monitoring. After studying the features and limitations of existing slope monitoring systems, it determined that there is a need to provide a reliable slope stability monitoring and prediction system by using a solar power-based long-range wireless sensor network for continuous monitoring of different prevailing parameters of slope stability. An accurate prediction of slope failure using a multiparameters-based prediction model is required for giving warning per the danger levels of impending slope stability. Considering the requirement, a slope failure monitoring and prediction system has been developed by the authors, using a wireless sensor network for the continuous monitoring of slope failure and to provide early warnings. The chapter describes details of slope stability mechanism, parameters affecting slope failure and triggering aspects, monitoring systems, prediction software, and laboratory experiments for calibrating geosensors and field installation of the developed system.

For practical purposes, the Earth’s crust is the only source of minerals. There are, of course, huge amounts of minerals in the Earth’s core and in space, but at the moment it is not possible for us to reach and use them.

Hard rock minerals could be mined from an asteroid or a spent comet. Precious metals such as gold, silver, and platinum group metals could be transported back to Earth, while iron group metals and other common ones could be used for construction in space.

Difficulties include the high cost of spaceflight, unreliable identification of asteroids which are suitable for mining, and ore extraction challenges. Thus, terrestrial mining remains the only means of raw mineral acquisition used today. If space program funding, either public or private, dramatically increases, this situation may change as resources on Earth become increasingly scarce compared to demand and the full potentials of asteroid mining—and space exploration in general—are researched in greater detail.

Asteroid mining could shift from sci-fi dream to world-changing reality a lot faster than you think. Planetary Resources deployed its first spacecraft from the International Space Station last month, and the Washington-based asteroid-mining company aims to launch a series of increasingly ambitious and capable probes over the next few years.

The goal is to begin transforming asteroid water into rocket fuel within a decade, and eventually to harvest valuable and useful platinum-group metals from space rocks. "After that, I think it's going to be how the market develops," Lewicki told Space.com, referring to the timeline for going after asteroid metals.

"If there's one thing that we've seen repeat throughout history, it's, you tend to overpredict what'll happen in the next year, but you tend to vastly underpredict what will happen in the next 10 years," he added. "We're moving very fast, and the world is changing very quickly around us, so I think those things will come to us sooner than we might think."