How Aliens Work

Are there other forms of life in the universe? The scientific search for extraterrestrial life forms has been bolstered by two recent discoveries. First, the discovery of life forms in exotic environments on Earth indicates that life is very hearty and can adapt to the strangest and most hostile environments. Second, astronomers found planets orbiting stars besides our sun — over 50 extrasolar planets have been discovered as of 2001. Are there alien life forms on any of these planets?

­

­If alien life does exist, what might it be like? Would it be simple forms of life such as bacteria, viruses or algae, or more advanced, multi-cellular creatures, perhaps even intelligent beings? Would aliens be animals, plants or have characteristics of both? Would they have arms and legs and walk upright as we do? Would they depend upon vision as their primary sense or use another way to gather information about their surroundings? Would they “breathe” oxygen or some other gas?

Speculation about aliens has typically been left to science-fiction authors, science-fiction readers and Hollywood writers and directors. In this article, we will examine astrobiology, the scientific search for extraterrestrial life. We’ll apply what we have learned about life on Earth to speculate about what alien life forms might be like.

Greetings, Carbon-based Bipeds!

Most of us picture alien life the way it’s portrayed in movies, where aliens are commonly depicted as human-like forms because they use actors either to play the roles directly in make-up or to be models for computer-generated animation. Also, audiences relate to human-like aliens better than to more exotic, monster-like creatures. However, the human body plan — bilateral symmetry with one head, two legs and two arms — stems from when early amphibians and reptiles colonized the Earth’s land masses, and it seems unlikely that such a shape would evolve on an alien world. So, let’s forget Hollywood for the moment and look closely at the real science of astrobiology.

Astrobiology is the scientific study of life in the universe. Astrobiologists seek to understand (among other things) how life arose and evolved on Earth, what governs the way life is organized and what makes a planet habitable.

Astrobiology combines the disciplines of biology, chemistry, physics, geology and astronomy. Often, astrobiologists must use the information learned about life on Earth as a guide for studying life elsewhere. Let’s examine some of the things that we have learned from life on Earth.

While it is hard to pen a clear definition of “life,” most biologists agree that there are many characteristics in common among living things. If an object meets these characteristics, it is considered alive:

Organized -Living things are made of atoms and molecules that are organized into cells. The cells in an organism can be either uniform or specialized for various functions. The cells can be further organized into tissues, organs and systems. Living things on Earth are quite diverse as to their organization and complexity.
Homeostatic – Living things carry out functions that keep them in a constant, relatively unchanging state called homeostasis. For example, your body has systems that keep your body temperature constant — you shiver if you’re cold, sweat if you’re hot.
Reproduces – Living things make copies of themselves, either exact copies (clones) by asexual reproduction or similar copies by sexual reproduction.
Grows/develops – Living things grow and develop from smaller and/or simpler forms. For example, a human begins life as a fertilized egg, developing into an embryo, fetus and then a baby. The baby subsequently grows into a toddler, adolescent and adult.
Takes in energy from the environment – Staying in a relatively constant, organized state violates the second law of thermodynamics, which states that the degree of disorder (entropy) of all objects increases. For a living organism to maintain organization, it must take in, process and expend energy. The way humans and other animals do this is by eating food and extracting energy from it.
Responds to stimuli – Living things respond to changes in their environment. For example, if a stimulus causes you pain, you respond by moving away from that object. If you place a plant near a well-lit window, the branches or shoots grow toward the light (phototropism). For protection, some animals change color to blend in with their surroundings (camouflage).
Adapted to its environment – The characteristics of a living thing tend to be suited for its environment. For example, the fins of a dolphin are flat and adapted for swimming. The wing of a bat has the same basic structure as the bones in a dolphin’s fin, but has a thin membrane that enables flight.
Now that we’ve got a definition of what life is, we need to look at how it changes over vast expanses of time. The basic rules governing whether species arise, live, remain unchanged or become extinct are those of evolution by natural selection as proposed by Charles Darwin. Darwin’s theory of evolution has the following points to it:

Similar organisms reproduce similar organisms — a dog reproduces a dog, a dandelion reproduces dandelions and a fish reproduces a fish.
Often, the number of offspring are overproduced such that the number that survive is fewer than the number reproduced.
In any population, individuals vary with respect to any given trait, such as height, skin color, fur color or shape of beaks, and these variations can be passed on to the next generation.
Some variations are favorable, in that they make those individuals best-suited to their environment, and some are not. Those organisms with favorable variations will survive and pass those traits on to their offspring; those individuals with unfavorable variations will die and not pass on their traits — this is natural selection.
Given sufficient time, natural selection will accumulate these favorable traits. The species will evolve.
Although Darwin’s theory of evolution was proposed to explain changes in Earth-based species, its principles are general enough that it could be applied elsewhere in the universe as well.

RARE EARTH HYPOTHESIS
The Drake equation, developed by astronomer Frank Drake and promoted by Carl Sagan, is used to estimate the number of intelligent civilizations in the universe. In contrast, geologist Peter Ward and astronomer Donald Brownlee from the University of Washington have proposed a hypothesis — the Rare Earth Hypothesis — that life on Earth is unique. Their hypothesis states that a series of chance events or situations, such as living in the habitable zone of the sun, having a Jupiter-type planet to clear away comet and asteroid debris and having few mass extinctions, has allowed life to develop on Earth and would be unlikely to happen elsewhere. See “Rare Earth: Why Complex Life is Uncommon in the Universe” for details.

Up until about 30 years ago, it was believed that all life on Earth was dependent upon energy from the sun. Furthermore, it was thought that you would probably not find life where temperatures were extremely hot, like in geysers or hot springs, or extremely cold, like in the Antarctic desert.

These ideas changed when oceanographers explored hydrothermal vents, openings in the ocean floor where extremely hot, mineral-rich water erupts from the crust. Hydrothermal vents are located several miles below the surface, on the ocean floor, where the surrounding water is at or near freezing, it is absolutely dark and the pressure is high. In organized communities around the bases of these vents, called black smokers, scientists found clams, crabs and exotic, giant tubeworms measuring 6 feet (2 meters) long. The water coming out of these vents is 230 to 662 degrees Fahrenheit (110 to 350 degrees Celsius).

How can these animals survive so far from the sunlight, under these extreme conditions? In the water, scientists found species of bacteria that split hydrogen sulfide from the water to get energy to make organic compounds (chemosynthesis). The tubeworms have bacteria in their tissues that help them derive energy from the water. The clams feed on the bacteria, and the crabs feed on the tubeworms.

The discovery of hydrothermal-vent communities showed that it is possible for life to evolve in places without light from the sun, and in other worlds without sufficient light from the parent star. In view of the discovery of hydrothermal vents, it may be possible that life exists on Europa, an icy moon of Jupiter, which scientists believe has a water ocean beneath its icy crust.
Life has been found in other extreme environments as well. Scientists discovered microcolonies of lichens called cryptoendoliths in rock samples of the Antarctic desert, where temperatures often drop to 100 degrees below zero and there is little or no liquid water. In contrast, thermophilic (heat-loving) bacteria have been found in hot springs where temperatures exceed the boiling point of water.
Living cryptoendoliths (green, black, green-blue lines) in a rock sample from Antarctica (left) and a thermophilic, rod-shaped bacteria (about 1 micron long) from a hot spring in Yellowstone National Park (right)

If life can evolve in extreme environments on Earth, it seems possible that life may exist in the extreme environments of other worlds such as Mars.

You may also like...