Gel 001 Medterm 1.0 Flashcards
1
Q
Our galaxy
A
Milky Way
2
Q
galaxies
A
huge collections of stars, held together by gravity
• hundreds of billions of galaxies in the universe
3
Q
solar system
A
Our solar system is one of over a hundred billion
star systems in our Milky Way galaxy
4
Q
Planets and Moon
A
Planets and moons grow and evolve from
the remnants of star formation
5
Q
Nebula
A
clouds of gas (H) and dust in space that mark the birthplace of stars
Every atom in the Sun, Earth, the other planets and moons, and you and me were in that cloud
6
Q
Solar Nebula hypothesis
A
proposes that the planets were formed from the disk of gas and dust that surrounded the sun as it formed
Driven by gravity and angular momentum, the nebula collapses into a rotating disk of gas and dust surrounding a central‘proto-star’
7
Q
star
A
Revolving masses of gas and dust not gravitationally
attracted into the evolving proto-star become trapped in
stable orbits, forming bands of concentrated material
Gravity supplies the energy to heat up and compress
the H gas, eventually forming a star at the center of
the rotating disk of gas and dust.
8
Q
Planetary Evolution
A
planetesimals —> proto-planets
9
Q
planetesimals
A
grow by collisions of gas and dust particles, increasing their - mass & gravity
– growth process called accretion
10
Q
proto-planets
A
Are formed when Planetesimals combine by collisions
11
Q
modern planetesimals
A
asteroid-
comet-
12
Q
asteroid
A
rocky planetesimal
13
Q
comet
A
icy planetesimal
14
Q
Proto-Earth
A
-Growth of planets from colliding planetesimals
-Proto-Earth was ‘soft’ and hot from countless collisions. Gravity shaped the mass into a sphere.
15
Q
Stars
A
-Our star contains ~99.85% of all the matter in the solar system
-Planets, moons, asteroids & comets form as a byproduct of star formation from nebula. They are the‘leftovers’ that didn’t get incorporated into the newly formed star at the center.
16
Q
Stars with disks
A
– young star with a broad disk of gas and dust.
- gaps form where growing young planets have gravitationally swept their orbits clear of gas and dust
17
Q
Meteorites
A
chunks of rock & metal that are remnants of the early solar system that didn’t become part of
the sun, planets or moons.
18
Q
radioactive elements
A
Dating of radioactive elements within meteorites yields
4.6 billion year age of Earth and the rest of the solar system
19
Q
Planets are born hot due to
A
-Heat of formation (aka ‘accretionary heat’) = frictional
heat accumulated through constant collisions
• Accumulation of radioactive elements (U, Th, K) that
‘decay’ to other elements, emitting heat in the process
20
Q
Differentiation of Earth
A
-Denser material sinks, lighter material rises
-Core, mantle, crust, hydrosphere, atmosphere
21
Q
Hadean Era (first 700 m.y.)
A
Young, ultrahot Earth - covered with a ‘magma ocean’
- differentiation driven by heat energy & gravity
22
Q
large-impact model for origin of the Moon
A
4.5 b.y. ago
- the impactor and much of Earth was melted or vaporized
23
Q
Moon
A
• Moon rapidly accretes from the disk of debris orbiting the young Earth
• both covered in magma oceans
• oldest moon rocks 4.48 b.y.
• axial tilt of Earth (seasons)
24
Q
Seasons
A
23.5 axial tilt created by the giant impact that formed the Moon is the reason for our seasons
25
Earth’s earliest solid crust
Formation of Earth’s earliest solid crust by
cooling of magma ocean (by about 4.0 b.y.)
26
Earth’s oldest known rocks
4.0 billion year old
-Acasta gneiss from northwest Canada
27
Where did Earth’s earliest atmosphere
& hydrosphere come from?
Volcanic outgassing - H2O, CO2, SO2, NO2, CH4
- outgassing from the magma ocean formed Earth’s earliest
atmosphere (no free oxygen)
28
Earth’s first oceans
With planetary cooling, eventual condensation of water
vapor into rain, accumulating in low areas on the surface to become Earth’s first oceans
- original water from asteroids & comets (planetesimals)
- released from Earth’s interior via volcanic outgassing
29
first oceans
first oceans by ~3.9 to 4.0 b.y.a.
- thick atmosphere, acidic oceans, heat release from volcanism and vents
30
first life
3.5 b.y.a. – first life (microbial & anaerobic)
31
Interior of the Earth
-Crust (0-40 km)
-Mantle (40-2890 km)
-Liquid iron outer core (2890-5150 km)
-Solid iron inner core (5150-6370 km)
32
What is Earth made of?
-Iron (35%)
-Oxygen (30%)
-Silicon (15%)
-Magnesium (10%)
SiO2 Silica (main component of rock)= Oxygen + Silicon
33
Pressure Density Temperature
- all increase toward the center of Earth
• 14.7 psi at sea level
• 1.5 million psi 200 miles below surface
• 50 million psi in central core
• 50° at surface
• 3000° 300 miles below surface
• 8500° at center of Earth
34
Mental
A greenish color
olivine-rich
35
Seismology
the study of earthquake waves and the deep interior of Earth
Earthquakes occur in the brittle rock of the crust
36
Seismologists
Seismologists measure the time it takes for earthquake waves to rebound back to the surface from boundaries inside the Earth, then convert to distance.
37
How do we know Earth’s core is mostly iron?
1) iron meteorites - derived from iron core of asteroid
2) From experiments in the lab, we know the characteristics of highly compressed iron
- consistent with an iron core
3) Abundance of Elements in the Universe
38
Asteroid Psyche
- iron-rich
- potentially the exposed iron core of a proto-planet
- potato-shaped, about the size of Massachusetts
- Psyche spacecraft to be launched by NASA this month
39
Why should we care about the Earth’s core?
Motion of metallic iron in Earth’s liquid outer core creates the magnetic field that surrounds our planet
• compasses
• deflection of charged particles from solar wind (protects life)
• evidence for plate tectonics
40
Sedimentary rocks
- layering / bedding / strata
- preserved records of climate, sea level & changing environmental conditions
- fossil evidence of evolution
41
Sedimentary rocks
Sedimentary rocks are the solidified products of clay, silt,
sand and other loose sediment originally deposited as
horizontal layers in various depositional environments.
42
river pouring sediment-laden water through a delta into open water
1 – weathering & erosion of highlands to produce loose sediment
2 – transportation downslope (by water, wind, ice)
3 – deposition in low regions (as horizontal layers)
4 - Burial, compaction and cementation of loose sediment into hard sedimentary roc
43
sandstorm off Saharan Desert
• erosion
• transportation
• deposition
oceans as ultimate sedimentary basin
44
iron oxide cement binding quartz grains
Ions transported in solution by groundwater. When the solution becomes concentrated enough in pores between grains, Fe oxide, calcite, or silica may precipitate as a cement.
45
Types of sedimentary rock
Sandstone: grains of sand
Shale: fine clay particles
Siltstone: silt particles
Conglomerate: cobbles, pebbles, sand, silt
46
sedimentary layer
Each sedimentary layer is a preserved record of climate, sea level & depositional environments at that place and time in Earth history
47
Superposition
Rocks represent phases of geologic time, and thus
act as archives of ancient environments and events
48
actualism
Interpretations of depositional environments are
based on the principle of actualism
= what we can actually see occurring in today’s
world is likely to have occurred in the past
49
Actualism
“The present is the
key to the past”
50
Modern Sandunes
Modern sand dunes aid in interpreting ancient sand dunes using
actualism as the guiding principle
51
Fossils
Fossils indicate:
1) depositional environment (trilobites are marine)
2) relative age of the rock (based on faunal change)
3) tangible evidence for evolution
fossilization
52
Redwall Limestone
- composed of mineral called calcite
53
Modern corals composed of CaCO3 (calcite)
- accumulation of calcite remains of coral debris and
other marine organisms (clams, oysters, algae, sponges)
forms sedimentary rock called limestone
54
modern limestone
Bahamas - modern limestone forming today
Great Barrier Reef, Northeast Australia
-continental margin
55
Modern limestone-forming
Modern limestone-forming regions occur in warm,
shallow tropical seas where corals and other calcite-shelled invertebrates prefer to live
56
sedimentary layers
• sedimentary layers record ancient history of changing
environments, sea level, and climate through time
• sedimentary rocks contain the fossil record of evolution
• sedimentary rocks aid in determining the geologic time scale
• all fossil fuels (coal, oil, natural gas) are found in
sedimentary rocks
57
Four Principles of Relative Age-Dating
1 Superposition - oldest at bottom, youngest at top
2 Original horizontality - sediments are deposited in
horizontal layers (controlled by gravity)
3 Cross-cutting relations
4 Faunal succession - based on progressive evolutionary
change revealed by fossils
58
Principle of Original Horizontality
exposure (outcrop) of horizontally bedded sedimentary rock
Gravity causes particles of sediment to fall to their lowest
possible position, resulting in horizontal bedding
Tilting of the layers had to occur after they
were originally deposited as horizontal beds
Folding of the layers had to occur after they were
originally deposited as horizontal beds (deformation)
59
Cross-cutting relations
Fault ‘cross-cuts’ the layers of rock, so faulting had to have occurred after deposition of the rock
1) deposition of sediment as horizontal layers (original horizontality)
2) burial and cementation to become sedimentary rock
3) tectonic uplift and tilting of the layers
4) weathering and river erosion to produce the landscape
deformation by folding and faulting “cross-cuts” the originally horizontal layers
60
Faunal succession
- based on progressive evolutionary change revealed by fossils
Evolutionary change creates a systematic succession of fossils with age, regardless of the location.
- i.e., the order of the fossils will always be the same, no matter where the rocks are found
61
Major events in the history of life
1) Precambrian: microbes (bacteria & archaea) 4.6 b.y
2) Cambrian ‘Explosion 540 Ma
3) Paleozoic: (Marine life)
4) mass extinction 250 Ma
5) Mesozoic: Jurassic era (Age of reptiles)
6) mass extinction 66 Ma
7). Cenozoic: Earths current geological era (Age of mammals)
8) Ice age begins
62
Numerical (radiometric) age dating
– placing specific ages on rocks
- works best on minerals (like zircon) that crystallize from a magma or lava (igneous rocks)
- as soon as the rocks solidify, radioactive decay begins
e.g., 512 (±1) m.y. vs. ‘younger than’ or‘older than’
63
zircons
– minerals that crystallize from a molten
melt, incorporate radioactive elements into their
atomic lattice, and remain very stable through time
64
radiometric age dating
uses naturally occurring ‘decay’ of radioactive elements within minerals to determine a numerical age
Numerical (radiometric) age-dating requires a mass
spectrometer to count the number of atoms of specific
elements. Absolute age then calculated by mathematics.
65
oldest Moon rocks
4.48 billion years
66
Integrating numerical age-dating with relative age-dating
Principles of Original horizontality & Superposition
Principle of Cross-cutting relations –
faulting occurred last because it cross-cuts the sedimentary & volcanic rocks
67
Radiocarbon dating:
- requires radioactive C-14
- useful for dating organic material containing carbon
- works back to about ~40,000 years
- important for anthropologists, archeologists, and historians, as well as geologists who study recent Earth history
68
Where does most of the energy for the world population come from?
• 82% of the world’s energy is derived from fossil fuels
• fossil fuels (coal, oil, natural gas) are non-renewable
resources
69
fossil fuel
The burgeoning use of fossil fuels beginning in the second
half of the 19th century is the primary reason for the rapid
growth of our global civilization
70
US primary energy consumption by energy source
Fossil fuels: ~79% of U.S. energy use
Solar & wind: ~4% but growing rapidly
71
ultimate source of most energy
The sun is the ultimate source of most energy on Earth, including fossil fuels.
fuels are the chemical residues of ancient plants that lived long ago.
“fossilized sunshine”
72
Where does coal come from?
derived from land plants accumulating in low-oxygen, swampy conditions
(~300 m.y. ago)
6CO2 + 12H2O + sunlight C6H12O6 + 6O2 + 6H2O
photosynthesis
73
coal swamp
Over millions of years, the coal swamp is buried under younger
sedimentary layers, compressing the organic debris and
concentrating the carbon (coal is a sedimentary rock)
74
How to get coal
-Uplift (mountain-building via tectonism) brings the coal beds up to the surface
-strip mining for coal
-underground coal mine
75
Coal in the US
U.S. has >25% of the world’s coal reserves
76
Electricity production by source, world, 1965-2022
• coal is the single largest source of energy to generate electricity
globally, with 36% of the total
• electricity production from solar and wind equaled 12% in 2022
77
Electricity generation in California, 2001-2020
~50% of California’s electricity came from zero-carbon renewable sources in 2020
78
carbon intensity:
the amount of CO2 emitted into the atmosphere per unit of electrical energy produced.
79
Oil & Natural Gas:
the fuel of our global economy and our addiction to it
-gasoline
-jet fuel
-personal products
-plastics
80
Oil
Transportation (gasoline, diesel, jet fuel) accounts for ~2/3rds of all
oil used in the U.S., with the rest going toward plastics and other
petrochemicals.
81
Where does oil & natural gas come from?
phytoplankton
6CO2 + 12H2O + sunlight C6H12O6 + 6O2 + 6H2O
photosynthesis
82
phytoplankton
“pelagic rain” to the seafloor
83
Oil, production steps
1) accumulation of organics and clay
-Plankton and Clay floating in water sinks in accumulate
2) burial - organic black shale
-More sediment accumulates over plankton, richlayer and compresses it
3) deeper burial- kerogen
-Organic rich mud turns to black shell. Under heat and pressure, kerogen forms
4) oil & natural gas generation & migration
-As temperature increases, kerogen turns to oil. The oil rises.
84
Oil and natural gas
Oil and natural gas are generated within organic black shales
organic black shale
- sedimentary source rock
85
Burning fossil fuels & the impact on the global climate
with combustion: potential energy stored in chemical bonds converts to usable heat energy accompanied by the release of CO2
6CO2 + 12H2O + sunlight C6H12O6 + 6O2 + 6H2O
C released at rates a million times faster than it took to accumulate
86
Cryosphere
– consists of continental ice sheets, ice shelves, glaciers, sea ice, and regions of permafrost
Cryosphere reflects solar energy back to space, influences deep-ocean circulation, drives major wind systems along the polar
front, and thus plays a critical role in world climate
87
Glaciers & Ice Sheets
mountain glaciers
-aka “alpine” or “valley” glaciers
– “rivers” of ice (& rocks & grit)
- a few hundred meters thick
Glaciers
-are large masses of ice (and rocky debris) that move downslope due to the force of gravity
88
accumulation
- snow transformed to ice by pressure and removal of air
89
ablation
- the removal of ice at the toe of a glacier by melting, sublimation (the evaporation of ice into water vapor), and/or calving of icebergs
90
Modern Continental Ice Sheets
- Antarctic & Greenland continental ice sheets hold ~99% of Earth’s ice
-Behave in response to same ice budget as mountain glaciers
- Antarctic ice sheet has >9 times the volume of ice of Greenland
91
West Antarctic & East Antarctic ice sheets
(separated by the Transantarctic Mtns)
-Highest continent on Earth, with average elevation of
8200’ (2500 m)
-Highest point on the ice sheet is 13,452’ (4100 m)
-If all ice on Antarctica melted, sea level would rise by 65 m (210 ft)
92
bedrock topography beneath Antarctic ice sheet
Revealed by ice-penetrating radar & other geophysical techniques
93
Greenland ice sheet
-Covers some 80% of the island, the icy measures more than 650,000 mi.². Shaped like a Lens the ice solid at its thick center, but rigid with decay around the edges.
-Ice, penetrating radar, offers a detail look at the land below. Every summer as the ice margin melts and glaciers slide faster into the sea, Greenland loses more than twice the amount of ice in the European Alps.
94
Arctic Ocean sea ice
-free-floating Arctic sea ice
-Arctic warming 4 times faster than the rest of the planet.
-Reflectance of solar energy back to space decreases with decreasing area of polar sea ice, enhancing climate warming
95
Response of ice sheets and mountain glaciers to global climate
-Greenland ice sheet is slowly losing mass
-Antarctic ice sheet is slowly losing mass
-Not all, but most alpine glaciers are receding worldwide
96
glacial meltwater
-glacial meltwater is entering the oceans, causing sea level to rise
-30-40% due to thermal expansion of seawater
97
albedo
- Both continental ice sheets and Arctic sea ice have high albedo (aka
‘reflectivity’) = proportion of incoming sunlight that is reflected back to space by a surface
- Earth’s average albedo is 0.3 (30% of incoming sunlight is reflected back to space)
98
Ice-Albedo feedback loop
As ice with snow cover melts, it is replaced by darker land or ocean water and their much lower albedo that absorbs more heat. The warmer temperatures promote more ice loss, amplifying the temperature increase.
99
Ancient Climate Change
-Icehouse phases
-Greenhouse phases
100
global temp-
-Modern average global temperature = 15° (59°)
Mid-Cretaceous average = 23° (73°)
-natural greenhouse effect
-“paleoclimatology”
101
Pleistocene Ice Ages- last 2.6 m.y
- Modern continental ice sheets – remnants of the most recent Ice Ages
-Antarctica 2-4 km thick
-Greenland 2-3 km thick
102
Pleistocene Ice Ages
began 2.6 m.y.a.
• ice sheets advanced and retreated multiple times
• map shows extent of ice sheets during Last Glacial Maximum
~20,000 yr ago
• 2-4 km in thickness
103
Maximum extent of ice sheets
-Maximum extent of ice sheets in northern
hemisphere 20,000 years ago
-ice sheets advanced and retreated multiple times over the full 2.6 m.y. of the Pleistocene Ice Ages
104
Sea-level
- Sea-level falls during major glaciations, accompanied by
coastline migration and the exposure of continental shelves
- Sea level fell 120 m (~360’) during Last Glacial Maximum
18-20,000 years ago
105
Bering land bridge
early human migration pathway
~15-20,000 yrs ago
106
How do geologists know that continental ice sheets grew then
receded multiple times during the Pleistocene ice ages?
Chemistry of foraminifera shells found in hundreds of sediment
cores from beneath the seafloor provides a measure of ocean
temperature through time
107
What controls rapid oscillations of climate during Ice Ages?
Milankovitch orbital cycles- caused by gravitational interactions with Sun, Moon, & planets (mostly Jupiter & Saturn)
108
Geochemical
- Geochemical evidence from foraminifera living in the Pleistocene oceans indicates 20-30 glacial advances (glaciations) and intervening warmer periods when glaciers receded (interglacials)
~6 to 10° global temperature variation between glacial & interglacial phases
109
Milankovitch cycles
Summing the variations in Milankovitch cycles provides a measure of the amount of solar radiation that reaches Earth’s surface (called insolation).
When the amount of solar radiation that reaches the surface is low, ice sheets expand. When solar radiation is high, ice sheets retreat.
110
Evidence from Ice Cores
Ice cores from Greenland and Antarctica provide a record of
atmospheric temperature and CO2 going back hundreds of
thousands of years preserved in gas bubbles trapped in the ice '
111
Climate change
Climate change – includes “global warming” but also sea level rise, ' shifts in ecozones, expansion of deserts, and an increase in extreme weather events
Weather – short-term (minutes to months) changes in the
atmosphere e.g., temperature, humidity, rainfall, cloudines
Climate – long-term average weather for a particular region
and time period (commonly ~30 years) e.g., deserts are
typically hot and dry, tropics tend to be hot and wet, polar regions are commonly cold and dry
112
natural greenhouse effect
-Earth’s average surface temperature is 15°C (59°), ideal for water to
take the form of a liquid and for life to proliferate.
-Without an atmosphere and a natural greenhouse effect, Earth’s surface temperature would be
-18°C (0°).
-Earth would be 33°C (59°) cooler without an atmosphere
with greenhouse gases (H2O, CO2, CH4, others)
113
greenhouse effect
- the connection between CO2concentration and global temperature
-The current 0.0418% CO2 in our atmosphere (along with
other heat-trapping gases) creates a natural greenhouse
effect that makes our planet habitable.
114
What are the sources of greenhouse gases?
- Water vapor (H2O)
-Carbon dioxide (CO2)
-Nitrous oxide (N2O)
-Methane (CH4)
115
Water vapor
(H2O)
Continuously recycled through hydrologic cycle, transferring heat
energy within Earth system
116
Carbon dioxide
(CO2)
-Continuously recycled through biosphere by respiration / photosynthesis
• natural sources include volcanism and wildfires
• new sources are fossil fuel burning and deforestation
117
Nitrous oxide
(N2O)
• natural byproduct of microbes in soils and ocean
• agricultural sources relate to N fertilizers for agriculture
118
Methane
(CH4)
• sources include rice cultivation, livestock, industry, natural gas leaks from wells and pipelines
• oxidizes to CO2 within a decade
119
Global Average Temperature Anomaly 1850-2023
The rate of warming in the past 15 years has been 40% higher than warming since 1970s 
120
What’s driving the warming trend?
- Atmospheric CO2 is the primary driver of global temperature since the Industrial Revolution
- Since the Industrial Revolution, CO2 is being added to the
atmosphere at ever-increasing rates by the combustion of fossil fuels and deforestation by humans
121
Global warming
“Global warming” is an enhanced greenhouse effect triggered by a
combination of fossil fuel combustion and deforestation that release
greenhouse gases.
122
What level of CO2 might we expect in the near future?
current rate of CO2 increase is >10 times faster than those of the recent geologic past
123
Consequences of a warming planet:
- Loss of continental ice mass
-Both the Greenland and Antarctic ice sheets are slowly losing mass
-The world ocean absorbs 90% of the excess heat in the atmosphere
Thermal expansion of ocean water contributes ~30-40% of sea level rise
-glacial meltwater is entering the oceans and warmer ocean water is expanding, causing sea level to rise
-Extreme weather events: The planet is getting hotter
-The planet is getting drier in places
-The planet is getting wetter in places
124
By 2100:
• 2-4° (3-7°) temperature increase
• 1-2 m rise in sea level
• shift in ecological zones
• increase in extreme storms, heatwaves, and drought
• expansion of deserts
• societal disruption
• climate refugees
• disproportionate effect on the poor
125
“Climate anxiety” is real among people 16-25
10,000 people age 16-25 surveyed from 10 countries
- Brazil, India, Nigeria, Philippines
- Australia, France, Finland, Portugal, U.K, U.S
126
Toward a more sustainable planet
-Toward a more sustainable planet – Energy Transitions
-Decarbonization of the global economy to limit the rise
of CO2 to <450 ppm and global temps to 2°C by 2100
-Requires rapid phase-out of fossil fuel sources, deployment of large-
capacity renewable sources, enormous increases in energy efficiency, development of long-duration energy storage (batteries), and other energy technologies not yet known
127
Solar power
- Solar power (including other renewables like wind power) will
need to supplant fossil fuels as our main electricity source
• Renewables are today a cheaper form of electricity than
coal and natural gas.
128
Electricity from Hydrogen
- Grey Hydrogen
Natural gas —> Hydrogen (CO2 leaks through the air)
- Blue Hydrogen
Natural gas —> Hydrogen (CO2 underground storage)
- Green hydrogen
Water \ Green electricity —> hydrogen (releases O2)
• Today, most hydrogen is produced from CH4
• “Blue” and “Green” Hydrogen is expensive
• $7 billion for regional hydrogen hubs to spur the
development of infrastructure and production
129
Toward a more sustainable planet-
electrification of transportation
Complete transition to electric vehicles with widespread infrastructure (w/ electricity generated by non-carbon emitting
sources)
130
Toward a more sustainable planet – Societal Solutions
- change in lifestyle in the developed world '
• conservation
• New Urbanism
• better mass transit
• corporate tax on carbon emissions
• economies based on less consumption
• voting for climate-aware candidates
131
Toward a more sustainable planet: Technological Solutions
-Active carbon capture from the atmosphere & sequestration underground (CCS)
- geoengineering – technological ideas to actively change
the amount of solar radiation reaching Earth’s surface
132
Toward a more sustainable planet: Socioeconomic Fixes
• reduce disparity between haves & have nots Richest 1% of global population accounts for more than double the emissions of the poorest 50%
133
Toward a more sustainable planet: Political Solutions
• $370 billion investment intended to reduce US emissions of GHGs by 40% from 2005 levels by 2030
• tax credits for electric vehicles, a network of charging stations, investments in sustainable batteries & solar energy technology
134
Toward a more sustainable planet: International collaboration
-on climate, fair trade, technology, population growth, income disparity
-Working collectively toward reducing our ecological footprint on the planet
135
Our solar system
Our solar system is composed of 8 planets, 4 dwarf planets like Pluto, about 290 moons, and countless asteroids and comets, all revolving along near-planar orbits around our star at the center.
136
Solar Nebula Hypothesis
Nebula are clouds of gas and dust in space that mark the birthplace of stars ("star nurseries"). Nebula are common throughout our galaxy and all galaxies. The gas and dust are the raw materials that
eventually build into a star and the system of planets and moons orbiting the star.
137
Nebula
- The gas is almost entirely hydrogen (which you know as the ' simplest element, consisting of one proton and one electron).
- hydrogen makes up about 75% of all the mass in the universe.
- The dust is composed of small amounts of various ices, oxides, carbon. and some heavier elements such as iron. (size of the dust is about the size of smoke particles, just a few molecules big)
The dust and gas composing a nebula are derived from the death of an earlier star. “You” were in that nebular cloud from which our solar system originated, but in the form of the original atoms that
eventually came together to compose you. Literally, the C atoms in your little finger, the K in the banana you just ate for breakfast, the Ca in your bones, and the Fe in your blood were once part of
this nebular cloud of gas and dust. In fact, every atom now in the sun, the planets and moons, as well as you and me was in that cloud.
138
origin of our solar system
Earth and the rest of the planets in our solar system formed
from the remnant gas and dust left over from the formation of our star, the sun.
139
Planetary Evolution
• In the orbiting rings around the young star, temperatures cool to the point where gas and dust begin to merge into larger and larger particles.
• As particles collide due to gravitational attraction, they grow into boulder- to asteroid-size objects called planetesimals. As planetesimals acquire more gas and dust, they grow in mass and thus gravity. The collisional growth of planets by constant bombardment is called accretion.
140
planetesimals
modern planetesimals are objects like asteroids (mostly rock) & comets (mostly ice). Asteroids are located primarily in the asteroid belt between the orbits of Mars and Jupiter, whereas icy comets
mostly reside in the Kuiper belt that surrounds the very outermost solar system beyond the orbit of Pluto.
- asteroids and comets are remnant planetesimals that didn’t become part of the Sun, planets or
moons
- robotic exploration of asteroids and comets shows them to be full of water, either frozen as ice or incorporated into the atomic structure of minerals
141
proto-planets.
• Within asteroids and comets orbiting lanes of gravitationally concentrated matter, collisions between planetesimals
cause them to grow into larger bodies called proto-planets. Their increased mass and gravity would
have helped to attract nearby smaller planetesimals and hold it all together. Eventually, larger
proto-planets evolve by accretion into larger true planets.
• The original shapes of the proto-planets were irregular, but heat built up due to frictional heating
through constant collisions. These hot, 'soft' early planets eventually were shaped into spheres
under the force of gravity.
142
accretion
So gas & dust combine by gravitational attraction to create planetesimals, and planetesimals combine via countless collisions to create proto-planets. Proto-planets grow and evolve to become planets.
This progressive enlargement is called accretion.
Planets, moons, asteroids and comets form as a byproduct of star formation from nebula. They are the ‘leftovers’ that didn't get incorporated into the newly formed star at the center.
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Meteorites
Meteorites are chunks of rock or metal that fall to Earth from space.
- most meteorites are derived from the fragmentation of asteroids during collisions in the asteroid belt between Mars and Jupiter. The asteroids in the belt are thought to be remnants of a ring of rocky
planetesimals that never accreted to become a planet
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Planets are born hot due to:
1) frictional heating through constant collisions (kinetic energy of infalling planetesimals converts to heat energy). This energy is called heat of formation (also called “accretionary heat”) and is a important
source of heat in the early stages of planets.
2) accumulation of radioactive elements (U, Th, K) that slowly ‘decay’ to other elements, giving off heat
in the process
