Category Life on Earth

As there are billions of planets in our universe, it is likely that some of them could support life, but the vast distances that would have to be travelled to reach them are at present an immense problem. More possible is the idea that humans could build self-supporting communities on nearby planets. Ideally, these would need to be enclosed, containing their own atmosphere and able to support a variety of plant and animal life just as our planet does. Experiments are being made t9 see if it is possible to build artificial ecosystems like this here on Earth.

We know of only one living planet: our own. But we know it very well. As we move to the next stage in the search for alien life, the effort will require the expertise of planetary scientists, heliophysicists and astrophysicists. However, the knowledge and tools NASA has developed to study life on Earth will also be one of the greatest assets to the quest.

There are two main questions in the search for life: With so many places to look, how can we focus in on the places most likely to harbor life? What are the unmistakable signs of life — even if it comes in a form we don’t fully understand?

“Before we go looking for life, we’re trying to figure out what kinds of planets could have a climate that’s conducive to life,” del Genio said. “We’re using the same climate models that we use to project 21st century climate change on Earth to do simulations of specific exoplanets that have been discovered, and hypothetical ones.”

Del Genio recognizes that life may well exist in forms and places so bizarre that it might be substantially different from Earth. But in this early phase of the search, “We have to go with the kind of life we know,” he said.

Further, we should make sure we use the detailed knowledge of Earth. In particular, we should make sure of our discoveries on life in various environments on Earth, our knowledge of how our planet and its life have affected each other over Earth history, and our satellite observations of Earth’s climate.

Above all else, that means liquid water. Every cell we know of — even bacteria around deep-sea vents that exist without sunlight — requires water.

The saying that there is nothing new under the Sun is strangely true. The stuff that makes up everything on Earth —animals, plants, rocks, water — cannot be destroyed, although it can be changed from one form to another. Living things are almost entirely made up of six elements: carbon, oxygen, hydrogen, nitrogen, phosphorous and sulphur. When a plant or animal dies, it decomposes. Gradually, its body breaks down, and the elements it was made of go back into the soil or water. These elements in time are taken up by new plants, which in turn are eaten by animals. This cycle of elements being released and re-used can take millions of years, but it is quite likely that within your body there are chemicals that were once part of a prehistoric plant — or even a dinosaur!

Eventually, all living things die. And except in very rare cases, all of those dead things will rot. But that’s not the end of it. What rots will wind up becoming part of something else. This is how nature recycles. Just as death marks the end of an old life, the decay and decomposition that soon follow provide material for new life. “Decomposition breaks apart dead bodies,” explains Anne Pringle. She’s a biologist at Harvard University in Cambridge, Mass.

When any organism dies, fungi and bacteria get to work breaking it down. Put another way, they decompose things. (It’s the mirror image of composing, where something is created.) Some decomposers live in leaves or hang out in the guts of dead animals. These fungi and bacteria act like built-in destructors.

Soon, more decomposers will join them. Soil contains thousands of types of single-celled fungi and bacteria that take things apart. Mushrooms and other multi-celled fungi also can get into the act. So can insects, worms and other invertebrates. Yes, rotting can be yucky and disgusting. Still, it is vitally important. Decomposition aids farmers, preserves forest health and even helps make biofuels. That is why so many scientists are interested in decay, including how climate change and pollution may affect it.

Decomposition isn’t just the end of everything. It’s also the start. Without decay, none of us would exist. “Life would end without rot,” observes Knute Nadelhoffer. He’s an ecologist at the University of Michigan in Ann Arbor. “Decomposition releases the chemicals that are critical for life.” Decomposers mine them from the dead so that these recycled materials can feed the living.

The most important thing recycled by rot is the element carbon. This chemical element is the physical basis of all life on Earth. After death, decomposition releases carbon into the air, soil and water. Living things capture this liberated carbon to build new life. It’s all part of what scientists call the carbon cycle. The carbon cycle starts with plants. In the presence of sunlight, green plants combine carbon dioxide from the air with water. This process, called photosynthesis, creates the simple sugar glucose. It’s made of nothing more than the carbon, oxygen and hydrogen in those starting materials.

Wind, moving water and sunshine are always to be found somewhere on the Earth. All of these can be harnessed to provide energy. Wind farms, consisting of fields of enormous windmills, have been set up in many parts of the world to capture the wind’s energy. Hydroelectric power uses the force of water hurtling over dams. Solar panels are warmed by the Sun and can be used to heat water and homes. At the moment, these methods are not able to produce all the energy that the world needs, but they hold out hope for the future.

A renewable resource is one that can be used repeatedly and does not run out because it is naturally replaced. A renewable resource, essentially, has an endless supply such as solar energy, wind energy, and geothermal pressure. Other resources are considered renewable even though some time or effort must go into their renewal (e.g., wood, oxygen, leather, and fish). Most precious metals are renewable also. Although precious metals are not naturally replaced, they can be recycled because they are not destroyed during their extraction and use.

A renewable resource is different from a nonrenewable resource; a nonrenewable resource is depleted and cannot be recovered once it is used. As the human population continues to grow and demand for renewable resources increases. Types of biofuel include biodiesel, an alternative to oil, and green diesel, which is made from algae and other plants. Other renewable resources include oxygen and solar energy. Wind and water are also used to create renewable energy. For example, windmills harness the wind’s natural power and turn it into energy.

The United States currently relies heavily on coal, oil, and natural gas for its energy. Fossil fuels are non-renewable, that is, they draw on finite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, the many types of renewable energy resources-such as wind and solar energy-are constantly replenished and will never run out.

Most renewable energy comes either directly or indirectly from the sun. Sunlight, or solar energy, can be used directly for heating and lighting homes and other buildings, for generating electricity, and for hot water heating, solar cooling, and a variety of commercial and industrial uses.

The sun’s heat also drives the winds, whose energy, is captured with wind turbines. Then, the winds and the sun’s heat cause water to evaporate. When this water vapor turns into rain or snow and flows downhill into rivers or streams, its energy can be captured using hydroelectric power.

Living things can grow and reproduce themselves. Given the right conditions, they can continue to do this for millions of years. But some of the Earth’s resources cannot renew themselves. When they have been used up, there will be no more. Perhaps the most important of these non-renewable resources are what are known as fossil fuels. Both oil and coal were made millions of years ago when the bodies of prehistoric plants and animals were crushed under enormous pressure beneath moving rock. There is a limited supply of these fuels, making it necessary for us to develop energy sources that cannot run out.

Renewable and nonrenewable resources are energy sources that human society uses to function on a daily basis. The difference between these two types of resources is that renewable resources can naturally replenish themselves while nonrenewable resources cannot. This means that nonrenewable resources are limited in supply and cannot be used sustainably.

There are four major types of nonrenewable resources: oil, natural gas, coal, and nuclear energy. Oil, natural gas, and coal are collectively called fossil fuels. Fossil fuels were formed within the Earth from dead plants and animals over millions of years—hence the name “fossil” fuels. They are found in underground layers of rock and sediment. Pressure and heat worked together to transform the plant and animal remains into crude oil (also known as petroleum), coal, and natural gas.  

The plants and animals that became fossil fuels lived in a time called Carboniferous Period, around 300 to 360 million years ago. The energy in the plant and animal remains originally came from the sun; through the process of photosynthesis, solar energy is stored in plant tissues, which animals then consume, adding the energy to their own bodies. When fossil fuels are burned, this trapped energy is released.

Crude oil is a liquid fuel fossil fuel that is used mostly to produce gasoline and diesel fuel for vehicles, and for the manufacturing of plastics. It is found in rocks below Earth’s surface and is pumped out through wells. 

Natural gas is widely used for cooking and for heating homes. It consists mostly of methane and is found near oil deposits below Earth’s surface. Natural gas can be pumped out through the same wells used for extracting crude oil.  Coal is a solid fossil fuel that is used for heating homes and generating power plants. It is found in fossilized swamps that have been buried beneath layers of sediment. Since coal is solid, it cannot be extracted in the same manner as crude oil or natural gas; it must be dug up from the ground. Nuclear energy comes from radioactive elements, mainly uranium, which is extracted from mined ore and then refined into fuel. 

Unfortunately, human society is—for the time being—dependent on nonrenewable resources as its primary source of energy. Approximately 80 percent of the total amount of energy used globally each year comes from fossil fuels. We depend on fossil fuels because they are energy-rich and relatively cheap to process. But a major problem with fossil fuels, aside from their being in limited supply, is that burning them releases carbon dioxide into the atmosphere. Rising levels of heat-trapping carbon dioxide in the atmosphere is the main cause of global warming. 

Alternative energy sources, such as wind and solar energy, are a possible solution to the depletion of nonrenewable sources. Both of these clean energy sources are available in unlimited supply.