Question 1

The best places for life to have formed on Earth are believed to have been

Accepted Answer

Liquid water is necessary for life as we know it to form and survive. The oceans and pools of water would provide a stable environment with the necessary water, nutrients, and energy sources for life to emerge and evolve. The frozen solid ice near the south pole would not provide the necessary conditions for life to form, and the areas with no water in Africa would also be unable to support life.

Question 2

As far as we know all forms of life on Earth use ____________ as a medium for chemical reactions.

Accepted Answer

Liquid water is the medium for chemical reactions used by all forms of life on Earth. Gaseous helium and frozen carbon dioxide and frozen water are not suitable mediums for life as they are not stable under normal Earth conditions.

Question 3

____________ is the molecule created in the cell nucleus that carries the information to make specific proteins out in the cell body.

Accepted Answer

The molecule that carries the information to make specific proteins is RNA. DNA serves as a template for RNA synthesis, but it is the RNA that carries the information from the nucleus to the cell body where proteins are synthesized. Enzymes are molecules that catalyze chemical reactions but do not carry genetic information. ALH84001 and PAH are not relevant to genetic information or protein synthesis.

Question 4

Why is it believed that life cannot evolve on a planet that orbits a spectral type A, B, or O star?

Accepted Answer

These stars, classified as spectral types A, B, or O, have relatively short lifespans on the main sequence, typically ranging from a few million to a few hundred million years. This period is considered too brief for the complex processes of life's evolution to occur, which, based on our understanding from Earth, can take billions of years.

Question 5

The number of technological civilizations in our galaxy is limited by

Accepted Answer

The number of technological civilizations in our galaxy is limited by a combination of factors, including the number of stars in our galaxy, the fraction of stars with planets, the number of planets per star in habitable zones longer than a few billion years, and the fraction of suitable planets where technical life forms evolve. All of these factors contribute to the likelihood of the existence of technological civilizations in our galaxy.

Question 6

Replicating early Earth conditions in the lab, the Miller experiment created from inorganic chemicals

Accepted Answer

The Miller experiment was able to produce amino acids, the building blocks of proteins, from inorganic chemicals under conditions that were thought to have existed on early Earth. However, it did not create life, DNA, or molds.

Question 7

A cell's DNA molecules contain its genetic material. An offspring born with altered DNA due to radioactivity, cosmic rays, or errors in reproduction

Accepted Answer

Offspring born with altered DNA due to various reasons are called mutants. Mutations can either have positive, negative, or neutral effects on the organism's survival, but the altered DNA itself does not increase the likelihood of survival.

Question 8

Presuming that it takes several billion years of complex live to evolve in a stable environment, the stars most likely to currently have inhabited planets with favorable conditions for life are

Accepted Answer

G to K main-sequence stars are the most common type of stars in our galaxy, and they have a stable lifespan of billions of years. Planets orbiting these stars are more likely to have the right conditions for life to evolve over time. B to A main-sequence stars are hotter and brighter than G to K stars, and their lifespan is shorter, which can reduce the time available for life to evolve on their planets. G to K giants are unstable and prone to flares and bursts of radiation, making it difficult for life to survive. White dwarf stars and neutron stars are remnants of dead stars and are unlikely to have the conditions necessary for life.

Question 9

Current searches for extraterrestrial intelligence use radio telescopes at wavelengths

Accepted Answer

Radio telescopes used for the current searches of extraterrestrial intelligence must use wavelengths longer than those emitted by Earth's atmosphere, which the atmosphere blocks, and shorter than the radio wavelength 'noise' naturally emitted by our galaxy, which can interfere with potential signals. This narrows the range of useful wavelengths for these searches.

Question 10

The oldest fossils on Earth

Accepted Answer

The oldest fossils on Earth, which are around 3.5 billion years old, were found in sedimentary rocks of ancient ocean beds. Therefore, it can be inferred that life began in the oceans.

Question 11

DNA is important to a cell because

Accepted Answer

DNA contains the genetic information necessary for the cell to make all of the molecules required by the organism, including enzymes, structural proteins, and signaling molecules. Additionally, DNA contains the instructions for cell division and reproduction, allowing the cell to pass on its genetic material to its daughter cells. While the cell membrane is important for regulating the movement of molecules in and out of the cell, it is not composed of DNA. Therefore, choices A and D are not correct.

Question 12

ALH 84001

Accepted Answer

ALH 84001 is a meteorite that was found in Antarctica and is believed to have originated from Mars. It contains tiny structures that some scientists believe could be evidence of early life on Mars.

Question 13

The most likely region of the radio spectrum for communication with other civilizations is the water hole, the part of the spectrum

Accepted Answer

The water hole is the region of the radio spectrum between the radio emissions of hydrogen (at 1420 MHz) and the hydroxyl molecule (OH) at 1665 MHz and 1667 MHz. This region is considered the most likely frequency for communication with other civilizations, as it is a region where there is very little natural background noise and is therefore an ideal frequency for transmission and reception of signals.

Question 14

The habitable zone around a star is

Accepted Answer

The habitable zone around a star is a region around a star where a planet's temperature would permit the existence of liquid water. This is important because water is necessary for life as we know it to exist.

Question 15

Why are massive main-sequence stars not likely to have planets that contain life?

Accepted Answer

Massive main-sequence stars have relatively short lifespans compared to smaller stars like the Sun. This short lifespan means they do not remain stable long enough for the complex processes necessary for life to evolve on any orbiting planets.

Question 16

The first complex multicellular life forms with appendages, etc., appeared on Earth about 0.5 billion years ago during the

Accepted Answer

The first complex multicellular life forms with appendages, etc., appeared on Earth during the Cambrian Period, about 0.5 billion years ago. This period is famous for the explosion of life forms, known as the Cambrian explosion, where a wide range of organisms with hard exoskeletons, shells, and other complex features emerged.

Question 17

A cell's DNA molecules contain its genetic material. DNA molecules contain patterns for the production of

Accepted Answer

DNA molecules contain specific sequences of nucleotides that code for the production of proteins. The genetic code is interpreted during protein synthesis to create specific amino acid sequences, which fold into functional proteins. While DNA also contains phosphates, sugars, and four kinds of bases, these molecules do not themselves code for the production of proteins.

Question 18

A cell's DNA molecules contain its genetic material. The DNA molecule can be altered

Accepted Answer

DNA can be altered by chance mismatching of base pairs during DNA replication or by damage from external factors such as exposure to radioactivity. The concept of a cell being "intelligent" and making deliberate changes to its DNA is not supported by current scientific understanding.

Question 19

A cell's DNA molecules contain its genetic material. These molecules are constructed of

Accepted Answer

DNA molecules are composed of nucleotides, which are made up of sugars (deoxyribose), phosphates, and nitrogenous bases (adenine, thymine, cytosine, and guanine). DNA does not contain amino acids or proteins in its own structure.

Question 20

What limitation(s) make it impossible to travel between stars?
I. fuel requirements
II. the tremendous distances between stars
III. the finite speed at which objects can travel

Accepted Answer

I, II, and III are all significant limitations for interstellar travel. Fuel requirements become exponentially larger the further you wish to travel (I). The distances between stars are vast, often measured in light-years, making current propulsion methods inadequate for timely travel (II). The speed limit of the universe, the speed of light, presents a fundamental barrier to how quickly we can move through space, making current technology insufficient for such journeys (III).

Quiz 20: Astrobiology: Life on Other Worlds