Question 1

Which measurement(s)would help determine absolute dates by radiometric means?

Accepted Answer

Both the accumulation of the daughter isotope and the loss of parent isotopes help determine absolute dates by radiometric means.

Question 2

If a fossil is encased in a stratum of sedimentary rock without any strata of igneous rock (for example, lava, volcanic ash)nearby, then it should be

Accepted Answer

Sedimentary rocks are formed from the accumulation of sediments, which can come from various sources and times, making it difficult to date them precisely using radiometric dating. This method works best with igneous rocks, which form from the cooling of magma or lava and can be dated by measuring the decay of radioactive isotopes present at the time of the rock's formation.

Question 3

Which of the following statements provides the strongest evidence that prokaryotes evolved before eukaryotes?

Accepted Answer

The statement that the oldest fossilized cells resemble prokaryotes provides the strongest evidence that prokaryotes evolved before eukaryotes as it suggests that the first living organisms on Earth were prokaryotes.

Question 4

An early consequence of the release of oxygen gas by plant and bacterial photosynthesis was to

Accepted Answer

Oxygen gas would react with iron in ocean water and terrestrial rocks, causing them to rust (oxidize). This is evident by the many iron formations found in rock layers before and after the Great Oxygenation Event.

Answer: E
 The release of oxygen gas eventually led to the formation of an ozone layer, which prevented harmful UV radiation from reaching the Earth's surface. However, at the onset of oxygenation, there would have been a period of time where there was insufficient ozone to block harmful UV radiation, leading to environmental stresses on early life forms.

Question 5

Recent evidence indicates that the first major diversification of multicellular eukaryotes may have coincided in time with the

Accepted Answer

The first major diversification of multicellular eukaryotes is thought to have coincided with the melting that ended the "snowball Earth" period, as this event significantly altered Earth's environments, making them more hospitable for complex life forms.

Question 6

If the half-life of carbon-14 is about 5,730 years, then a fossil that has one-sixteenth the normal proportion of carbon-14 to carbon-12 should be about how many years old?

Accepted Answer

The fossil has 1/16 the normal proportion of carbon-14, which means it has gone through 4 half-lives (since 2^4 = 16). Multiplying the half-life of carbon-14 (5,730 years) by 4 gives 22,920 years, which rounds to option E, 22,900 years.

Question 7

How were conditions on the early Earth of more than 3 billion years ago different from those on today's Earth?

Accepted Answer

Early Earth was intensely bombarded by large space debris, which is not the case today. The atmosphere was reducing, not oxidizing, and lacked significant ozone, allowing more ultraviolet radiation to penetrate.

Question 8

If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then one should be surprised to observe evidence of which of the following within such microfossils?
I.double-stranded DNA
II.a nuclear envelope
III.a nucleoid
IV.a nucleolus
V.ribosomes

Accepted Answer

Evidence of a nuclear envelope (II) and a nucleolus (IV) within microfossils from 3.2-billion-year-old stromatolites would be surprising because these features are characteristic of eukaryotic cells, which are believed to have evolved much later than 3.2 billion years ago. Double-stranded DNA (I), a nucleoid (III), and ribosomes (V) are features that could be expected in both prokaryotic and eukaryotic organisms, which could have existed at that time.

Question 9

Which of the following factors weaken(s)the hypothesis of abiotic synthesis of organic monomers in early Earth's atmosphere?
1)the relatively short time between intense meteor bombardment and the appearance of the first life-forms
2)the lack of experimental evidence that organic monomers can form by abiotic synthesis
3)uncertainty about which gases comprised early Earth's atmosphere

Accepted Answer

Explanation: The short time between meteor bombardment and the appearance of life (1) and uncertainty about the gases in early Earth's atmosphere (3) both challenge the hypothesis of abiotic synthesis. However, there is experimental evidence supporting abiotic synthesis, so 2 is not a valid factor.

Question 10

The synthesis of new DNA requires the prior existence of oligonucleotides to serve as primers. On Earth, these primers are small RNA molecules. This latter observation is evidence in support of the hypothesized existence of

Accepted Answer

The fact that RNA molecules serve as primers suggests the existence of earlier genetic systems based on RNA, as RNA can both store genetic information and catalyze chemical reactions. This supports the hypothesis that RNA preceded DNA as the genetic material in early life forms.

Question 11

Approximately how far back in time does the fossil record extend?

Accepted Answer

The fossil record extends back approximately 3.5 billion years, which is the age of the oldest known stromatolite fossils. Fossils from organisms with hard shells, bones, or other body parts can be found in rocks that are a few hundred million years old, while more recent fossils can be found in rocks that are only a few thousand years old.

Question 12

What is true of the fossil record of mammalian origins?

Accepted Answer

The fossil record of mammalian origins includes transitional forms with progressively specialized teeth, such as the synapsids that evolved differentiated molars, and the early mammals that evolved specialized incisors, canines, and molars.

Answer: D
 The fossil record of mammalian origins indicates that mammals and dinosaurs did not overlap in geologic time, as the first mammals evolved after the extinction of dinosaurs at the end of the Cretaceous period.

Answer: A, B, E
 None of the choices A, B, or E are true of the fossil record of mammalian origins. Choice A, regarding punctuated equilibrium, may apply to some lineages of organisms, but not necessarily to mammalian evolution. Choice B, regarding the common origin of birds and mammals, is not supported by the fossil record, as birds evolved from a different group of dinosaurs (theropods) than the ancestors of mammals (synapsids). Choice E, regarding the evolution of fur from scales, is not supported by the fossil record, as there is no direct evidence of intermediate stages between reptilian scales and mammalian hair.

Question 13

The first genes on Earth were probably

Accepted Answer

There is strong evidence that RNA was the first genetic material on Earth. RNA can act as both genetic material and a catalyst, making it a plausible candidate for the first self-replicating system. It is likely that the first genes on Earth were auto-catalytic RNA molecules.

Question 14

What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?
1)origin of mitochondria
2)origin of multicellular eukaryotes
3)origin of chloroplasts
4)origin of cyanobacteria
5)origin of fungal-plant symbioses

Accepted Answer

The correct sequence starts with the origin of cyanobacteria, which are among the earliest forms of life on Earth. Following this, the origin of mitochondria and chloroplasts through endosymbiotic events occurred, leading to the development of complex eukaryotic cells. Multicellular eukaryotes then evolved, and finally, symbiotic relationships such as fungal-plant symbioses developed.

Question 15

If natural selection in a particular environment favored genetic systems that permitted the production of daughter "cells" that were genetically dissimilar from the mother "cells," then one should expect selection for which of the following?
I.polynucleotide polymerase with low mismatch error rates
II.polynucleotide polymerases without proofreading capability
III.batteries of efficient polynucleotide repair enzymes
IV.polynucleotide polymerases with proofreading capability
V.polynucleotide polymerases with high mismatch error rates

Accepted Answer

If natural selection favored genetic systems that produced daughter cells genetically dissimilar from the mother cells, it would select for mechanisms that increase genetic variability. Polynucleotide polymerases without proofreading capability (II) and those with high mismatch error rates (V) would increase the likelihood of mutations, thereby increasing genetic diversity among offspring.

Question 16

What is true of the Cambrian explosion?

Accepted Answer

Recent studies have shown that the Cambrian explosion may not have happened as abruptly as once believed, with some fossils appearing in strata just below the Cambrian. Additionally, the explosion happened over tens of millions of years rather than a single instant.

Question 17

Which of the following is the correct sequence of events in the origin of life?
I.formation of protobionts
II.synthesis of organic monomers
III.synthesis of organic polymers
IV.formation of DNA-based genetic systems

Accepted Answer

The most widely accepted sequence of events in the origin of life is the synthesis of organic monomers (II) followed by the synthesis of organic polymers (III), leading to the formation of protobionts (I). Only after these events did the formation of DNA-based genetic systems (IV) occur. Choice C is the correct sequence in the given options.

Question 18

Several scientific laboratories across the globe are involved in research concerning the origin of life on Earth. Which of these questions is currently the most problematic and would have the greatest impact on our understanding if we were able to answer it?

Accepted Answer

Understanding how RNA sequences came to carry the code for amino acid sequences would have the greatest impact on our understanding of the origin of life as it would provide insight into how the first organisms could have formed and evolved. This process is known as the RNA world hypothesis and is still a topic of much debate and research. Answers to the other questions would also be important for understanding the origin of life, but they would not have as great of an impact as answering question C.

Question 19

What is true of the amino acids that might have been delivered to Earth within carbonaceous chondrites?

Accepted Answer

Carbonaceous chondrites have been found to contain a wider variety of amino acids than those that are used by living organisms on Earth today, indicating a rich chemical diversity in these space rocks.

Question 20

Which of the following is a defining characteristic that all protobionts had in common?

Accepted Answer

A surrounding membrane or membrane-like structure is a defining characteristic that all protobionts had in common. Protobionts are considered as the first step towards the formation of cells, and they are defined by their self-assembled structures that possess a selectively permeable membrane. This membrane-like structure provided separation from the external environment and allowed for the exchange of materials essential to life, such as nutrients and waste. Enzyme synthesis, RNA genes, and RNA replication are not necessarily defining characteristics of protobionts.

Quiz 25: The History of Life on Earth

Which measurement(s) would help determine absolute dates by radiometric means?

If a fossil is encased in a stratum of sedimentary rock without any strata of igneous rock (for example, lava, volcanic ash) nearby, then it should be