Chapter 12: The Search for Life
The habitable zone of a planetary system is defined to be the region where
planetary surfaces permit the existence of liquid water.
Abiogenesis Model
says that the original self-replicating molecule that led to Earth life formed spontaneously from non-living material here on Earth. suggests that any life that we find on Mars or on the Moons of the Jovian planets would not have Earth-type DNA and might even be using an entirely different scheme for reproducing itself.
In SETI programs, the "water hole" refers to
the range of signal frequencies between emissions caused by hydrogen and hydroxyl molecules.
If we wish to find life with a carbon-return process similar to the one here on Earth, we should look for planets
with thin, unstable surfaces.
Compared to the frequency of photons absorbed during a transition from a -5ev state to a -4ev state, transitions from the -5ev state to a -2ev state would correspond to absorbing photons whose frequency is
3 times as high.
Which of the following statements best describes the presence of water on Mars? A Mars probably had liquid water flowing on its surface at some time in the past. B At the present time, Mars is completely without water in any form. C Mars has liquid water flowing steadily on its surface at the present time. D At the present time, Mars is completely covered by a thin layer of frozen water ice.
A Mars probably had liquid water flowing on its surface at some time in the past.
DNA
A complex molecule containing the genetic information that makes up the chromosomes. adenine to thymine, guanine to cytosine A DNA molecule acts as a template for making a copy of itself by splitting each nitrogenous base pair to make two half-ladders which then act as patterns to form their missing halves.
Ultraviolet light is sometimes described as either UV-A or UV-B. The UV-B variety is supposed to be more damaging to your skin. You can conclude that of the two types, the UV-B variety has the A higher frequency. B lower frequency. C higher intensity. D lower intensity.
A higher frequency.
When ice melts, the resulting liquid water occupies A less volume than the ice did. B the same volume that the ice did. C more volume than the ice did.
A less volume than the ice did.
Which of these is a statement of the Fermi Paradox?
Any long-lasting technological civilization should be obvious and might even be visiting us, so where are they?
Compared to the frequency of photons absorbed during a transition from a -6ev state to a -4ev state, transitions from the -6ev state to a -2ev state would correspond to absorbing photons whose frequency is A the same. B 2 times as high. C 3 times as high. D 4 times as high. E 5 times as high.
B 2 times as high.
In current Earth life, the self-copying molecule that contains the information needed to construct and operate a life-form is A chlorophyll. B DNA. C RNA. D glucose. E glycoaldehyde.
B DNA.
The search for extrasolar planets has started to find "super-Earths," planets several times as large as Earth but with about the same density. From what we understand so far about plate tectonics on Earth, how likely is it that these super-Earths would have active surfaces like ours? A Impossible because these planets are the wrong size. B Possible if other conditions are also present. C Certain because all you need is size.
B Possible if other conditions are also present.
Which of the following models for the formation of life on Earth would most likely apply if it turns out that the first step of forming a self-copying molecule is rather easy and happens as soon as conditions are right for it? A The Abiogenesis Chimera Model. B The Abiogenesis Model. C The Panspermia Model. D The Spontaneous Generation Model.
B The Abiogenesis Model.
A technological civilization that lasts for astronomically significant periods of time should make an obvious and visible impact on the galaxy and should have figured out how to visit us by now. That leads to the question "So, where are they"? This statement and question is usually referred to as A The Drake Equation. B The Fermi Paradox. C The Copernican Principle. D The Twin Paradox. E The Third Law of Thermodynamics.
B The Fermi Paradox.
Suppose that some very strange creatures are found in a long-isolated place such as underneath the ice of Antarctica. Which of the following would be the strongest evidence that these creatures are descended from a different `first replicating molecule' than the rest of life on Earth? A The creatures are powered by heat-driven Iron and Sulfur chemistry instead of by sunlight. B The creatures use amino acid molecules that are mirror-images of the usual ones. C The creatures use several amino acid sequences that Earth life does not normally use. D The creatures use RNA as their basic genetic information-storage material instead of DNA. E The creatures absorb chlorine and excrete carbon tetracholoride.
B The creatures use amino acid molecules that are mirror-images of the usual ones.
Suppose that you observe a planet that reflects mostly green light and absorbs both red and infra-red light. Which of the following conclusions can you make? A The planet has Earth-type green plants on its surface. B The planet does not have Earth-type green plants on its surface. C The planet could have Earth-type planets or just green rocks There is no way to tell.
B The planet does not have Earth-type green plants on its surface.
Which of these moons could have two levels of oceans, with oceans of liquid hydrocarbons on the surface and oceans of liquid water beneath the surface? A Ganymede. B Titan. C Enceladus. D Europa.
B Titan.
Civilizations capable of sending out broadcast messages that we could possibly detect across interstellar distances would have to be technologically advanced and would probably be much more advanced than we are. That makes it difficult to decide what sort of signals they would send. The SETI program has decided to listen for microwave signals rather than more exotic types of signals (such as laser light, gamma rays, neutrinos, gravitational waves, etc.). The main reason for this choice is that A microwave technology will always be easier to use than more exotic communication technologies, even for unknown advanced civilizations. B a microwave signal can send the largest amount of information for a given amount of energy used to generate the signal. C a microwave signal can be beamed directly at us, greatly increasing the signal strength that we receive. D a microwave signal is easier to receive by less advanced civilizations and thus would have a wider potential audience.
B a microwave signal can send the largest amount of information for a given amount of energy used to generate the signal.
An advantage of carbon dioxide as the starting form of carbon for use by living things is that it A freezes to form dry ice. B dissolves in liquid water. C is the result of burning carbon.
B dissolves in liquid water.
A spectrum is defined to be the set of A energy levels in a light source. B frequencies or colors present in a light source. C frequencies or colors missing from a light source. D energy levels missing from a light source. E photons present in a light source.
B frequencies or colors present in a light source.
The range of distances of a planet from its primary star that will permit the existence of liquid water on the planet's surface is called the A water hole. B habitable zone. C inner system. D triple point.
B habitable zone.
The second most common element in the universe is A water. B helium. C silicon. D hydrogen. E carbon.
B helium.
If there is life on one of the Jovian moons, we would expect that life to most likely be A on the surface, using solar energy through photosynthesis. B in the subsurface oceans, using chemical and thermal energy. C in the surface lakes of liquid hydrocarbons, using tidal energy. D in the rocks, using magnetic energy.
B in the subsurface oceans, using chemical and thermal energy.
The range of signal frequencies between absorption bands caused by hydrogen and hydroxyl molecules A is always avoided by SETI programs because signals there are strongly absorbed. B is referred to as the "water hole" and is the frequency band that SETI programs usually choose. C is referred to as the "hydrogen band" and is usually avoided by SETI programs. D has no particular significance for SETI programs.
B is referred to as the "water hole" and is the frequency band that SETI programs usually choose.
If we wish to find life with a carbon-return process similar to the one here on Earth, we should look for planets A with thick, stable surfaces. B larger than Mars. C with volcanoes.
B larger than Mars.
The original source of energy for life forms that live near a black smoker is A always the Sun by means of dead plant and animal matter that falls from the surface of the ocean. B often chemicals generated by the heat of the Earth's interior. C often tube worms. D often bacteria.
B often chemicals generated by the heat of the Earth's interior.
An RNA molecule consists of A one long chain of amino acids with sugar phosphate molecules attached to the side of it. B one sugar phosphate chain with single nitrogenous bases attached to the side of it. C two sugar phosphate chains connected by pairs of nitrogenous bases. D two long chains of nitrogenous bases connected by pairs of sugar phosphate molecules.
B one sugar phosphate chain with single nitrogenous bases attached to the side of it.
The fact that the surface of Mars shows no tectonic activity means that one of the requirements for continuing life might be missing. A An energy source. B Liquid water. C A carbon-return process. D A portable form of carbon.
C A carbon-return process.
A multiple star system close to the Earth that is known to have stable orbits in the habitable zones of each of its stars is A Epsilon Aurigae. B Albireo. C Alpha Centauri. D Sirius. E Procyon.
C Alpha Centauri.
The closest star to Earth (other than the Sun) is part of a multiple star system called A Epsilon Aurigae. B Albireo. C Alpha Centauri. D Sirius. E Procyon.
C Alpha Centauri.
Which of the following systems is closest to the plan of most current Earth life-forms? A One DNA molecule carries out all of the chemical processes needed to construct and operate a life-form. B One RNA molecule carries out all of the chemical processes needed to construct and operate a life-form. C One DNA molecule is used to make RNA molecules which, in turn make the proteins and enzymes that construct and operate a life-form. D One RNA molecule is used to make the proteins and enzymes that carry out all of the chemical processes needed to construct and operate a life-form. E Lots of RNA molecules copy themselves and also act as enzymes which construct and operate a life-form.
C One DNA molecule is used to make RNA molecules which, in turn make the proteins and enzymes that construct and operate a life-form.
When a hydrogen atom on one molecule is attracted to an oppositely charged part of another molecule, the result is A a new molecule. B a salt. C a hydrogen bond. D a covalent bond.
C a hydrogen bond.
Here is the Drake Equation. In this equation, n_{e} stands for the A expected lifetime of a communication-capable civilization. B number of communication-capable civilizations in our galaxy. C average number of habitable planets in a planetary system. D number of extraterrestrial messages that we might expect to detect in a year. E average number of new stars that form in a year.
C average number of habitable planets in a planetary system.
The molecules of both water ice and liquid water are attached to one another by A ionic bonds --- Each molecule carries a net charge. B covalent bonds ---Nearby molecules share electrons. C hydrogen bonds --- .Different parts of each molecule have opposite charges. D Van der Waals bonds --- Small changes in charge distribution in one molecule induces changes in another
C hydrogen bonds --- .Different parts of each molecule have opposite charges.
Which of the following types of radiation has the lowest frequency on this list? A ultraviolet light. B green light. C infrared light. D X-rays. E red light.
C infrared light.
Because different molecules vibrate with distinctive radio frequencies, it is possible for radio telescopes to identify the chemical compounds that are present in interstellar clouds. When they look for complex compounds (more than four atoms) they find A no such compounds at all. B mostly Silicon compounds. C mostly carbon compounds. D about the same numbers of Silicon compounds and Carbon compounds.
C mostly carbon compounds.
One of the experiments carried out by the Viking Landers was to use a mass spectrometer to analyze the gas given off from a heated soil sample. The results of that experiment (as interpreted at the time) established that Martian soil contains A more carbon compounds than would be expected on a planet with a carbon-dioxide atmosphere. B just about the amount of carbon compounds that would be expected on a planet with a carbon-dioxide atmosphere. C no carbon compounds at all. D large organic hydrocarbons.
C no carbon compounds at all.
The two hydrogen atoms in a water molecule are both attached A to the oxygen atom, on exactly opposite sides of the oxygen atom. B to each other to form a pair that is then attached to the oxygen atom. C to the oxygen atom, but offset so that the molecule looks bent.
C to the oxygen atom, but offset so that the molecule looks bent.
As of July, 2018, The number of confirmed exoplanets found by the transit photometry method is closest to A 10. B 50. C 1250. D 2500. E 25,000.
D 2500.
The eclipse or transit photometry method of searching for exoplanets can be expected to find A any exoplanets that are out there. B all exoplanets that are Jupiter-size or larger. C about half of all exoplanets. D less than one out of every 10 exoplanets.
D less than one out of every 10 exoplanets.
Most plants here on Earth are green because the process of converting carbon dioxide and water into organic matter uses only A green light. B red light. C blue and violet light. D red, blue, and violet light. E red, blue, green, and violet light.
D red, blue, and violet light.
If the frequency of electromagnetic radiation goes from 6×10¹⁴Hz, to 2×10¹⁴Hz, the energy of each individual photon in the radiation A does not change. B is multiplied by 2. C is divided by 2. D is multiplied by 3. E is divided by 3.
E is divided by 3.
Which of the following systems do most living things on Earth now use to reproduce themselves?
Each DNA molecule splits in half and each half acts as a pattern to complete its other half.
Vegetation Red Edge
Green plants absorb red light but are strong reflectors of infra-red light, just below red in frequency. Infra red photons do not have enough energy for normal chlorophyll to split water directly, so absorbing them would result in waste heat, which plants do not want, so the plants reflect them.
Which of the following statements qualifies as a falsifiable working hypothesis of the sort that Karl Popper would favor?
Life arose on Earth and exists only there.
Which of the following features in the light reflected from a planet would indicate the presence of Earth-type plants (rather than just colored rocks) on its surface?
Red light is not reflected, but infra-red light is strongly reflected.
frequency and color
The range of frequencies that corresponds to visible light is rather narrow compared to the enormous range of frequencies for all the types of electromagnetic radiation An electromagnetic wave that is oscillating at 750THz (7.5×1014 cycles per second) would be seen as violet light. A wave oscillating at 566THz would be seen as green light . A wave oscillating at 430THz would be seen as red light.
The Viking Landers carried out several experiments on Martian surface soil. The final conclusion from those experiments (as interpreted at the time) was:
The surface of Mars is extremely hostile to all forms of organic matter.
Panspermia Model
based on the discovery that material from impacts on other planets has been deposited on Earth. Because bacterial spores and extremophile bacteria are known to be extremely hardy, they could have survived long space trips and brought life to Earth from elsewhere. suggests that we will find exactly the same DNA and the same biochemical processes everywhere that is within range of whatever process carried the original seeds of life.
The main reason to suspect that Titan has a subsurface ocean of water is
landmarks that are not rotating with the rest of the moon.
Photons
light particles equation: ephoton = hf where Ephoton is the energy of a single photon, f is the frequency of the wave and h is a constant, called Planck's constant High frequency light corresponds to high energy photons Low frequency light corresponds to low energy photons. Light can only be emitted or absorbed as photons.
A hydrogen bond is the result of
the electrical attraction between a hydrogen atom on one molecule and an oppositely charged part of another molecule.
If we detect that the intensity of the light from a star is mostly constant but drops slightly to a new constant value for a while and then returns to its normal level and repeats this behavior at regular intervals, we can reasonably suspect that
the star has a planet in orbit around it.
The main reason that the SETI@home system needs to use the computing power of 5.2 million participating home computers is that
they are collecting and analyzing signals from millions of different radio channels.
black smokers
vents on the sea floor that form as hot mineral -rich water rushes from the hot rock at mid-ocean ridges and mixes with surrounding cold ocean water