Chapter 25

Question 1

Deep Time

Answer 1

Geologic time is divided into four eons​

Eons are subdivided into eras, which are further subdivided into periods

Question 2

Geological evidence suggests a meteor hit the earth

Answer 2

4.6 billion years ago (BYA)

Question 3

CO2 levels shifted and affected temperature

Answer 3

Early atmosphere high CO2 levels.​

Water slowly vaporized from the molten rock.

Question 4

Increased weathering converted silicate rock to soil

Answer 4

CO2 formed carbonic acid.​

Carbonic acid released bicarbonate ions​

Decreases in CO2 lowered Earth’s temperature

Question 5

Continents moved over geological time

Answer 5

Earth’s crust formed rigid slabs of rock called plates

Question 6

Two supercontinents formed

Answer 6

Rodinia (all continents).​

Gondwana (all current Southern Hemisphere continents).​

Pangea (formed from Gondwana).

Question 7

Proterozoic (“early life”) eon occurred​

Answer 7

Two billion years into Earth’s history.

Question 8

Rodinia broke up before…

Answer 8

the Phanerozoic eon​

Question 9

Birds and mammals have existed for

Answer 9

4% of earth’s existence.

Question 10

Humans present for

Answer 10

0.2% of earth’s history

Question 11

Popular view of early atmosphere.

Answer 11

Carbon dioxide (CO2).​

Nitrogen gas (N2).​

Water vapor (H2O).​

Hydrogen gas (H2).​

Other sulfur, nitrogen, and carbon compounds.

Question 12

Miller-Urey experiment

Answer 12

In 1953, Miller and Urey did an experiment that reproduced early atmosphere​

Assembled reducing atmosphere rich in hydrogen with no oxygen gas.​

Atmosphere placed over liquid water.​

Temperature below 100° C.​

Simulate lightning with sparks.

Question 13

Miller-Urey experiment

Answer 13

Found within a week that methane gas (CH4) converted into other simple carbon compounds

Later experiments produced more than 30 carbon compounds including amino acids​

Adenine also produced.

Question 14

Evolution of metabolism

Answer 14

Primitive organisms may have been autotrophic or heterotrophic

Question 15

Landmarks in the evolution of metabolism

Answer 15

Oxygenic photosynthesis.​

Carbon fixation.​

Nitrogen fixation.

Question 16

Lipid bubbles

Answer 16

increase the probability of metabolic reactions

Question 17

Conditions on early Earth

Answer 17

Seems likely that Earth’s first organisms emerged and lived at very high temperatures​

Around 3.8 BYA ocean temperatures dropped to 49° to 88° C​

First organisms emerged around this time​

Question 18

Fossil evidence of life

Answer 18

Evidence of life during the Archean in the form of microfossils is difficult to find and interpret​

Two main formations of 3.5- to 3.8-billion-year-old rocks have been found​

Kaapvaal craton (South Africa) and Pilbara craton (Australia)​

Structures in each interpreted to be biological in origin.

Question 19

Microfossils

Answer 19

Microfossils are fossilized forms of microscopic life​

Oldest are 3.5 billion years old; seem to resemble present-day prokaryotes.​

Fossils from 3.2 BYA could be eukaryotic cells but probably cyanobacteria

Question 20

Stromatolites

Answer 20

Stromatolites are mats of cyanobacterial cells that trap mineral deposits​

Indirect evidence for ancient life.​

Oldest are 2.7 billion years old.​

Modern forms are also known.

Question 21

Isotopic data

Answer 21

c12 into cells before other carbon isotopes

Work has been done dating and analyzing carbon compounds in the oldest rocks, looking for evidence of life; carbon fixation active as long as 3.8 BYA​

Ancient carbon fixation via Calvin cycle or a reductive version of the citric acid cycle​

Ability to fix carbon has evolved more than once

Question 22

Biomarkers

Answer 22

Look for evidence of ancient organic molecules of biological origin​

Simple in theory but difficult to find​

Hydrocarbons derived from fatty acid tails of lipids were found in ancient rocks​

Analyzed for carbon isotope ratios to indicate biological origin.​

Indicates that cyanobacteria are at least 2.7 billion years old.

Question 23

Earth’s Changing System​

Answer 23

Climate (temperature and water availability) and atmosphere among many factors that affect organisms’ survival​

Dramatic shifts in all these factors led to mass extinctions influencing the course of evolution

Question 24

Shifts in atmosphere

Answer 24

Geological changes explain many changes in atmosphere​

Hot wet climate of tropics accelerated weathering; Snowball Earth decreased temperature and slowed weathering​

Plate tectonics can also affect weathering and atmospheric levels of CO2

Question 25

Continental motion affected evolution

Answer 25

Continents sit on submerged plates that are in motion​

Shifting plates affect evolution by reproductively isolating populations or allowing previously separate populations to interbreed

Question 26

Cenozoic era began 66 mya

Answer 26

Australia and Antarctica separated, as did Greenland and North America.​

The Atlantic Ocean continued to grow as plates in the mid-Atlantic spread.​

Greenhouse conditions during Cretaceous period led to a rise in sea level and continental areas were submerged.

Question 27

Life changes Earth

Answer 27

Oxygenic photosynthesis produced atmospheric O2​

200-million-year lag between the origins of photosynthesis and substantial levels of O2​

Iron oxide in the oceans.​

O2 in the atmosphere interacted with ultraviolet (U V) radiation from the Sun and formed O3 (ozone).

Question 28

Life changes Earth

Answer 28

Growing evidence that plants contributed to two glaciations​

Colonization of land by plants followed by gradual cooling and abrupt glaciation 488 to 444 mya.​

Vascular plants diversification concurrent with second glaciation 400 to 360 mya.

Question 29

Life evolved into three monophyletic domains

Answer 29

Eubacteria, Archaea, and Eukaryotes.

Question 30

Eukaryotes divided into 5 supergroups

Answer 30

Excavata​

SAR (Stramenopila, Alveolata, and Rhizaria)​

Archaeplastida​

Amoebozoa​

Opisthokonta

Question 31

Compartmentalization of cells

Answer 31

Compartmentalization of cells enabled the advent of eukaryotes​

Bacteria and archaea ruled the Earth for 1 billion years.​

Bacteria and archaea are distinct from eukaryotes in that they have much less compartmentalization.

Question 32

Evolution of endomembrane system

Answer 32

Infolding of the cellular membrane​

Nuclear membrane, not found in bacteria and archaea, accounts for increased complexity in eukaryotes.​

Physical separation of transcription and translation adds additional levels of gene expression.​

Golgi apparatus and endoplasmic reticulum facilitate intracellular transport.​

Not all cellular compartments are derived from endomembrane system

Question 33

Endosymbiosis and the origin of eukaryotes

Answer 33

Mitochondria and chloroplasts entered early eukaryotic cells by endosymbiosis​

Mitochondria are the descendants of the parasite Rickettsia, incorporated into cells early in the evolution of eukaryotes​

Chloroplasts are derived from cyanobacteria

Question 34

Multicellularity leads to cell specialization

Answer 34

Unicellular body plan tremendously successful​

Unicellular prokaryotes and eukaryotes constitute about half of the biomass on Earth.​

But a single cell has limits with cell specialization.​

Multicellularity allowed organisms to deal with environment in novel ways through differentiation

Question 35

Multicellularity leads to cell specialization

Answer 35

Multicellularity has arisen independently in different eukaryotic supergroups​

Multicellularity requires that cells connect to each other and communicate​

Gene expression varies among cells to allow specialization

Question 36

Sexual reproduction increases genetic diversity

Answer 36

Sexual reproduction allows greater genetic diversity​

Meiosis​

Crossing over​

First eukaryotes were probably haploid​

Diploids arose on separate occasions by fusion of haploid cells

Question 37

Rapid diversification occurred during the Cambrian

Answer 37

Evolutionary innovations occurred while life was primarily aquatic​

Established the foundations for tremendous diversity.​

Extremely rapid expansion of life called the Cambrian explosion (542 to 488 MYA).​

First multicellular animals appeared 50 million years following Cambrian explosion.

Question 38

Major innovations allowed for the move onto land​

Answer 38

Plants and then animals colonized terrestrial environments after Cambrian radiation​

Evolution of photosynthesis protected organisms on land.​

Ozone layer protected from U V light.​

Successful movement from water to land required innovations to prevent desiccation and to obtain water.

Question 39

Cambrian Period showed diversification of

Answer 39

multicellular organisms