Chapter 28: Life in the Universe

Comic evolution

___________ is a continuous transformation of matter and energy that has led to the appearance of life and civilization on our planet.

Particulate, Galactic, Stellar, Planetary, Chemical, Biological, and Cultural

What are the seven stages of cosmic evolution?

Organisms possessing the capacity for self-sustaining chemical systems capable of Darwinian evolution.

What defines life?

1. They can react to their environment and can often heat themselves when damaged

2. They can an grow by taking in nourishment from their surroundings and processing it into energy

3. They can reproduce, passing along some of their own characteristics to their offspring

4. They have the capacity for genetic change and can therefore evolve from generation to generation and adapt to a changing environment

What are the four characteristics of a living organism?

assumptions of mediocrity; 1. Because life on Earth depends on just a few basic molecules 2. Because the elements that make up these molecules are common to all stars 3. If the laws of science we know applied to the entire universe then given sufficient time, life must have originated somewhere else in the cosmos.

The general case in favor of extraterrestrial life is summed up in what are called _____________, which state that:

Suggests that the conditions necessary for complex life are extremely rare and possibly unique to Earth.

What does the opposing view for extraterrestrial life state?

Drake equation

The ________ attempts to determine the likelihood that intelligent life exists within our Galaxy in terms of specific factors with roots in astronomy, biology, and anthropology.

No, but it gets us thinking about possible answers and breaks the problem down into smaller pieces that we can start thinking about.

Does the Drake equation give us a hard and fast answer about whether life exists within our solar system?

The Rate of Star Formation

What is the first factor in the Drake equation?

Dividing the total stars (100 billion stars) by total time (10 billion years) = 10 stars/year

How do we estimate the rate of star formation in our Galaxy?

The star formation rate (10 stars/year)

What is the factor of the Drake equation that we can estimate the most confidently?

Fraction of Stars Planetary Systems; values of 1 because planets form around all stars.

What is the second factor of the Drake equation and what value do we assign this factor in our optimistic view?

Presence of liquid water, knowing atmospheric conditions, and temperature.

What is the most important factor that determines if a planet is habitable?

Range of distances within which a planet of mass and composition similar to Earth’s would have a surface temperature between the freezing and boiling points of water.

What is the stellar habitable zone of a star?

Range of distances from the Galactic center that are thought to be favorable for life.

What is the Galactic habitable zone?

Number of Habitable Planets per Planetary System; value of 1 and its based on out current observations that there is probably one habitable planet for every 10 planetary systems found.

What is the third factor of the Drake equation and what value do we assign this factor in our optimistic view?

Fraction of Life-Bearing Planets on which intelligence arises; value of 1 because we assume that natural selection is a universal phenomenon.

What is the fourth factor of the Drake equation and what value do we assign this factor in our optimistic view?

Fraction of planets on which intelligent life develops and uses technology; value of 1 because technology seems useful and desirable rather than something that should be rejected.

What is the fifth factor of the Drake equation and what value do we assign this factor in our optimistic view?

The average duration that a technologically advanced civilization can communicate or exist before disappearing or changing significantly; value commonly estimated to be around 1,000 to 100,000 years.

What is the average lifetime of a technologically advanced civilization?

100 years

About how long has our civilization been technologically advanced?

Ability to communicate over interstellar distances

What is the textbook’s requirements for a civilization to be technologically advanced?

number of technological intelligent civilizations now present in the Milky Way Galaxy = Average lifetime of a technologically competent civilization in years

In our optimistic view of intelligent life in the Galaxy, we come up with a simplified version of Drake’s equation, which becomes:

It won’t happen in our lifetime because if our neighbors are 2,500 lightyears away, when we send them a message by the time they receive it our civilization will be dead.

Why is it not likely that we can communicate with even our nearest intelligent neighbors?

Search for extraterrestrial intelligence; We have launched interstellar probes containing information about humans in case they should reach extraterrestrial intelligence.

What is SETI, and what has this organization done in an attempt to communicate with extraterrestrial life?

To find out if we are alone in the universe.

What is SETI’s justification for searching for extraterrestrial life?

Radio waves because they do not become scattered easily while traveling through dusty interstellar space.

What is the best type of electromagnetic radiation for communicating with extraterrestrial life?

The water hole is the range of wavelengths between 18 and 21 cm at which it’s thought we should search for signals from ET life. There is minimal “noise”, or signals, from other things in the universe at these wavelengths, which might falsely appear to be signals from ET life.

What is the range of wavelengths we believe we should “listen” at to receive signals from intelligent extraterrestrial life?

Allen Telescope Array

What telescope is SETI using in northern California to “listen” for signals from extraterrestrial life?

Particulate evolution

The first step in cosmic evolution is:

Cultural evolution

The last step in cosmic evolution is:

Biological evolution

During which step in cosmic evolution did diverse life forms begin to arise?

Stellar evolution

During which step in cosmic evolution were the chemical bases for life created?

The average survival time of the civilizations

Assuming the conditions ripe for life and intelligence abound in the Galaxy, what factor limits the number of galactic civilizations?

100 years

According to our definition, we have been a technological civilization for about:

Their lifetime is too short.

Why do we feel type O and B stars are poor candidates for extraterrestrial life?

Average lifetime of a civilization.

If we are optimistic in our assumptions about the development of life and intelligence, then the number of technological civilizations in the galaxy should equal the:

The region around each star where terrestrial planets could have liquid water on their surfaces

What is meant by the "habitable zone"?

One that can communicate over interstellar distances

How does Drake define a technological civilization?

The number of technical civilizations in our galaxy presently

The Drake equation calculates N. What is N?

100

Evidence gathered from observations of exoplanets indicates approximately what percentage of stars have planets?

A civilization that can communicate over interstellar distances

How is a technical civilization defined?

Not known; insufficient data to compute.

The Drake equation now tells us that the number of technological civilizations in our Galaxy at this time is:

The star formation rate in the Milky Way.

Taking the total number of stars in the Milky Way and dividing by the age of the Milky Way is a way to estimate:

About a tenth

Of the planetary systems that may exist in our galaxy, what fraction may contain a habitable planet?

Radio wavelengths

Most SETI searches are done at:

Pioneer 10

The first probe carrying mankind's message to alien civilizations was:

19 cm wavelength

Which of these radio waves would fall in the "water hole"?