Historical Geol.xlsx - Historical Geol Flashcards
(203 cards)
1
Q
Examines the origin and evolution of the Earth, its continents, oceans, atmosphere, and life
A
Historical Geol
2
Q
Some key concepts in histotical geol
A
The Earth’s surface have changed over geologic time
The rocks record the changes that occurred over geologic time
Interdisciplinary approach = comprehensive geologic “story
3
Q
Explain Neptunism; who theorized it
A
─ Rocks formed from crystallization of minerals in the ocean.
─ Earth originally consisted of water, then suspended materials settled to form the core and the continents.
─ Abraham Gottlob Werner
4
Q
Explain Plutonism/Vulcanism; who theorized it
A
─ Rocks formed from intrusive magmatic activity, which were then eroded and deposited on the seabed, re-formed as sedimentary rocks by heat & pressure, then raised again.
─ First proposed by Abbe Anton Moro (1750) and later used by James Hutton
5
Q
Explain Catastrophism; who popularized it
A
─ Landscape shaped by sudden, short-lived, worldwide violent catastrophes. Each epoch ended with these events based on extinction and succession in the fossil record.
─ Popularized by Georges Cuvier; anchored from Neptunism
6
Q
Explain Uniformitarianism or Gradualism; who conied it
A
─ Assumes that the natural laws and processes operating in the present time have operated in the past.
─ Geologic change occurring slowly over long time periods
─ Coined by William Whewell, proposed by James Hutton (1785; anchored from Plutonism), refined by John Playfair, and popularized by Charles Lyell.
7
Q
Explain Neocatstrophism; who where behind it
A
─ Sudden extinctions by high-magnitude, low-frequency events (disastrous but seldom catastrophes) like asteroid impacts.
─ “Steady-state” Uniformitarianism can’t explain episodic particularities in the fossil or rock record
─ First by Schindewolf (1963), then Alvarez (1980s)
8
Q
Explain Actualism; who where behind it
A
─ Modern belief that most geological processes are gradual yet there are periods of abrupt change.
─ Same process but different intensity and duration
─ Georges Louid Leclerc, Comte de Buffon
9
Q
Explain relative dating
A
─ Comparison of strata to determine an ordered sequence of events in geologic history
─ “Which is older” and not “How old”
─ Stratigraphic Principles
10
Q
Explain absolute dating
A
─ Gives accurate numerical ages of geologic materials to determine their ages.
─ “How old” and not “Which is older”
─ Experimental methods
11
Q
Explain The principle of Superposition
A
In an undisturbed sequence of strata, each bed is older than the bed above it and younger than the bed below it.
12
Q
Explain The principle of Original Horizontality
A
Each stratum must have been originally deposited in a horizontal manner.
13
Q
Explain The principle of Lateral Continuity
A
Each stratum is deposited continuously in all directions unless (1) hindered by an obstacle, (2) the supply has run out, or (3) has reached at the basin’s edge.
14
Q
Principle of Cross-cutting Relationships
A
Geological objects that cuts or displaces another is younger.
15
Q
Who were the people behind Principle of Cross-cutting Relationships
A
Developed by Steno, formulated by Hutton, elaborated by Lyell. 14
16
Q
Lyell’s Principle of Inclusions
A
Any geologic feature (rocks, minerals, fragments) included within another is older than the enclosing medium.
17
Q
Smith’s Principle of
Fossil Succession
A
Fossils succeed one another vertically in a definite and determinable manner which can be identified over wide distances.
18
Q
Buried erosional or non-depositional surface separating two rock units of different ages indicating a “halt” in the deposition of sediments.
Represents time with no deposition, hence “missing rock” in the record.
A
Unconformity
19
Q
is the missing time.
A
Hiatu
20
Q
Separates strata of two different dip angles. Records a period of strata deformation followed by stable depositional conditions
A
Angular Unconformity
21
Q
Separates igneous/metamorphic rocks and sedimentary strata.
Records either a period of exposure of magmatic rocks followed by sediment deposition, or by magmatic rocks intruding into sedimentary strata.
A
Nonconformity
22
Q
Separates parallel sedimentary strata.
Records period of erosion and/or non-deposition of sedimentary rocks atop older sedimentary strata. Common in tectonically-stable area and in basins.
A
Disconformity
23
Q
Separates parallel sedimentary strata but with no obvious erosional surface between them; needs fossil evidence to validate.
A
Paraconformity
24
Q
are short paraconformities (short interruption with little or no erosion).
A
Diastems
25
Unconformity that truncates the younger strata as they deposit atop older layers. Occurs when young sediments are deposited against older strata or exposed rock,
Buttress Unconformity
26
Disconformity or nonconformity with no distinct surface or contact but consists of materials derived from the underlying rock.
Blended Unconformity
27
Technique of placing geologic information distributed over widely-separated outcrops to create an accurate chronological profile of an entire geologic period or locality.
May be based on lithology, fossils, ages, magnetic polarity, unconformity, etc.
Steno’s Correlation
28
unstable parent nucleus emits two protons and two neutrons.
Alpha decay,
29
electron is emitted from a neutron in the nucleus.
Beta decay
30
a proton captures an electron and is thereby converted to a neutron.
Electron capture
31
is time it takes for 1/2 of the original unstable parent element to decay into the new stable daughter element
Half Life
32
C 14 Half Life
5730 years
33
H 3 Half Life
12.35 years
34
Pu 239 Half Life
24 065 years
35
Ra 222 Half Life
3.8 days
36
Bi 212 Half Life
60.55 minutes
37
Sr 85 Half Life
64.84 days
38
Sr 89 Half Life
50.5 days
39
Sr 90 Half Life
29.12 years
40
U 235 Half Life
703 my
41
U 238 Half Life
4.4 by
42
Uses 14C to date organic matter.
Radiocarbon Dating
43
14C has a half-life of 5,730 years, so it is used to date any material of up to
60,000 years old
44
Uses radioisotope 40K with a half-life of 1.3 billion years.; This is used to calibrate the Geomagnetic Polarity Time Scale
40K - 40Ar Dating
45
Dates materials to the last time they were heated. As radiation is absorbed, electrons within the minerals are freed producing light in the process.
Thermoluminescence
46
Dating method using the patterns of tree rings (growth rings) and is used to date the time these rings have formed
Dendrochronology
47
Maximum Age for Dendrochronology
11k years
48
Segment of the Earth’s history represented and recorded in the strata.
Geologic Time
49
is divided based on the relative age relationships in vertical stratigraphic position and fossils content (used to recognize in global scale)
Relative Time (Chronostratic)
50
is divided based on radiometric dating methods on rock types, yielding numerical ages.
Absolute Time (Chronometric)
51
observed rock beds with shell fossils located above sea level and viewed as once-living; implied transgression & regression
Xenophanes and Colophon
52
reasoned that land and sea positions changed over long time periods
Aristotle
53
wrote the concept of stratification, and recognized fossils as “petrifications of the bodies of plants and animals”
Avicenna
54
postulated that Earth is 6,000 years old
Bishop James Ussher
55
established stratigraphic principles in his book “De solido intra solidum naturaliter content dissertationis prodromus
Niels Stensen
56
postulated Earth is 75,000 years old based from hot iron balls cooled down and related to a similar-sized Earth
Georges Louis de Buffon
57
believed a 100 million years old based on the uniform decay of thermal structure as observed to present surface gradient
William Thomson, Lord Kelvin
58
believed a 100 million years as age based on the salt contents of the ocean and the erosion rate of sodic & potassic rocks to raise the ocean salinity to present levels; first to apply radioactivity method
John Joly
59
postulated 1.6 – 3.0 billion years based on the Uranium (U-Pb decay); formulated the modern geologic time scale
Arthur Holms
60
System of chronological dating used as a representation of time and events based on the rock record.
Geologic Time Scale
61
the International Chronostratigraphic Chartwas created by
the International Commission on Stratigraphy (ICS) of the International Union of Geological Sciences (IUGS)
62
used the terms “montes primarii” for rocks formed before the Deluge, and “monticulos secundarios” for rocks from the debris
Thomas Burnet
63
rocks formed before the Deluge
montes primarii
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rocks from the debris.
monticulos secundarios
65
According to the plutonists, the primary rocks are ____ and ____ while the secondary rocks are ____
Igni and Meta; Seds
66
pioneered the systematic rock divisions using stratigraphy and fossils. Local names were given and rocks are correlated across continents; Chronostratic
William Smith, and Georges Cuvier and Alexandre Brogniart
67
formulated the modern GTS using radioactive dating, enhanced by the discovery of isotope and mass spectrometry; Chronometric
Arthur Holms
68
In 2023, the Anthropocene Working Group of SQS proposed to designate the Anthropocene as a new geological epoch, based on radionuclides such as Plutonium as physical markers with ________________as reference for the globally-synchronous event marking the end of Holocene.
Crawford Lake in S. Canada
69
why did the IUGS downvoted the Anthropocene epoch proposition
> epoch division too large
> temporal scale
> epochs start after worldwide extinction
> societal rather than geological; designate as event rather than epoch
> timing
70
Hadean Eon duration
4.6 – 4.0 Ga
71
Archean Eon duration
4.0 – 2.5 Ga
72
Proterozoic Eon duration
2.5 Ga – 538 Ma
73
Phanerozoic Eon duration
538 Ma – present
74
Describe Geochronology
- measures age of materials and gives temporal distribution (fancy talk of saying time divisions)
- uses radioisotopes, paleomags, etc. to get age
- Time Units
75
Describe Chronostratigraphy
- Studies rock strata ages by relating to each other ( like which formed first)
- sequence and order or rocks during deposition
- Rock Units
76
Describe Time units
- Divides by Late, Middle , and Early
- How Old?
77
Describe Rock units
- Divides by Upper, Middle, and Lower
- Which is Older
78
Geochronologic vs Chronostratigraphic Units
Eon - Era - Period - Epoch - Age
Eonothem - Erathem - System - Series - Stage
79
2nd largest time unit; composes the Eon
Era/Erathem
80
There are 10 defined eras
Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Meso-Proterozoic, Neoproterozoic, Paleozoic, Mesozoic, and Cenozoic Eras
81
3rd largest unit; composes the Era
Period / System
82
Oldest and most recent period/system
Siderian (Proterozoic); Quaternary (Cenoic)
83
sub-periods for Carboniferous
Mississippian and Pennsylvanian Periods
84
2nd smallest geochronologic unit
Epoch/Series
85
Oldest and most recent epoch/series
Terreniuvian Epoch (Cambrian Period); Holocene Epoch (Quaternary Period)
86
Smallest hierarchical unit; composes the Epoch
Age/Stage
87
Oldest and most recent Age/Stage
Fortunian Age (Terreneuvian Epoch); Meghalayan Age (Holocene Epoch)
88
Non-hierarchical formal unit of unspecified rank
Used to correlate with Magnetostratigraphi, Lithostratigraphic or Biostratigraphic Units
Chron / Chronozone
89
Reference points in the stratigraphic section defining the lower boundary of a Stage, marked by gold spike.
Global Boundary Stratotype Section and Point (GSSP)
90
Considerations for the GSSP designatio
> defines the stage's lower boundary
> lower boundary defined by prinmary marker
> thick enough outcrop and cant be affected by tectonic, sedmentary, and metamorphic processes
91
- Chronological reference point and criterion in geologic record to define boundaries between chronostratigraphic units in a stata.
- Primarily used for rocks older than Ediacaran that lacks a good fossil record
Global Standard Stratigraphic Age (GSSA)
92
Observable diameter is
93 billion light years
93
age of the universe
13.78
94
main contents of the universe based on Lambda CDM model
Baryonic (ordinary matter) - 4.9%
Dark Matter - 26.8
Dark Energy - 68.3
95
Calculated the circumference of the Earth, instigating a curved shape of the Earth’s surface rather than a flat surface.
Eratosthenes
96
Earth was the center of the universe while the stars, planets, and other heavenly bodies revolved around it
Geocentric Model
97
who made the geocentric model
Ptolemy (150 CE) in his Almagest
98
Earth and planets revolved around the Sun.
Heliocentric Model
99
Who were behind the Heliocentric Model
Nicholas Copernicus (1543), supported by Galileo and Kepler
100
Universe is expanding but maintains a constant average density
Steady State Theory
101
Who proposed the Steady State Theory
Sir James Jean in 1928
102
Universe is continuously expanding from an initial state of high density and temperature (the Singularity
Big Bang Model
103
Who proposed the Big Bang theory
Georges Lemaitre, 1927
104
the big bang theory are supported by which concepts
Supported by the Red Shift (Doppler Effect), the CMB, the Hubble-Lemaitre Law.
105
explain the Hubble Lemaitre Law
the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth
106
predates the explosion; the point of infinite density, temperature, and curvature where all known physical laws collapse (become meaningless)
Cosmological Singularity
107
Evidences of the Big Bang
1. Red Shift and Doppler Effect
2. Hubble – Lemaitre Law
3. Cosmic Microwave Background
4. Abundance of lighter elements
108
is the alteration of a wave’s frequency relative to its distance from the observer. Distant galaxies emit light at the red spectrum, indicating very far distance. Conversely, near objects emit light in the blue spectrum.
Doppler Effect
109
Accurate method of calculating the distance of an object from a certain perspective relative to background.
Parallax
110
relates a body’s position as observed from Earth at specific time, and compares that body’s location in space as then observed again from Earth after 6 months
Stellar Parallax
111
Arno Penzias and Robert Wilson, 1965
Cosmic Microwave Background
112
Sequence of Events during the Big Bang
1. Plank
2. Grand Unification
3. Electroweak Epoch
4. Inflationary Epoch
5. Early Thermalization
6. Electroweak Breaking
7. Quark Epoch
8. Hadron Epoch
9. Lepton Epoch
10. Photon Epoch
Nucelosynthesis
11. Matter Domination
12. Recombination &
Photon Decoupling
13. Dark Ages
14. Reionization Epoch &
Earliest Galaxies
15. Population II & I Stars
16. Dark Energy Era
113
as expansion continues, universe becomes larger, colder, more dilute. All structures decompose to sub-atomic particles & photons.
Heat Death
114
expansion accelerates and so extreme that spacetime is pulled apart and unable to exist.
Big Rip
115
expansion stops then reverses and all matter accelerates towards the common center.
BIg Crunch
116
collapse of quantum fields results to annihilation of all current particles (and anti-particles) and form new forces and particles
Vacuum Instability
117
Expansion of Singularity; 4 forces still combined
Plank Epoch
118
Grand
Unification
Epoch
Gravity
separates;
physical
characteristics
meaningless
119
Inflation
Epoch
Cosmic inflation
& supercooling;
Quark-Gluon
Plasma forms
120
Hadrons
forms,
including
Baryons
Quark
Epoch
121
Hadrons
destroyed
emitting
light
Hadron
Epoch
122
Lepton
Epoch
Leptons
dominated,
then were
destroyed
123
Photons dominated,
interacting with other
baryons.
Nuclear fusion (from
2 mins to 20 mins)
Photon
Epoch
124
Only photons were
source of light; CMB
shifted into infrared,
and universe is
devoid of visible light
Dark
Ages
125
force separated first after the Big Bang
Gravity
126
Who where behind the solar nebular model
Accepted theory by Immanuel Kant (1755); modified by Pierre Laplace (1795)
127
growth at the expense of smaller planetesimals
Runaway Accretion
128
growth of largest planetesimals
Oligarch Arccretion
129
embryos merge with other; Mercury & Mars, water on Earth
Merger State
130
where a core is formed then enveloped by accreted gas.
Nucleated Instability Model
131
Duration of the Hadean Eon
4.567 Ga to 4.0 Ga.
132
explain the Iron Catastrophe
Iron and Nickel melted and sank to form the core, created the magnetosphere, while buoyant oxygen-seeking rocks rose and formed the primitive crust
133
in this model of explaning the formation of Earth's layers, immiscible liquid NiFe globules in a silicate magma sank and separated
Rain Out Model
134
Moon was part of the Earth (from Pacific Ocean) and later separated.
Fission Theory
135
Moon & Earth condensed individually and separately from solar nebula
Condensation Theory
136
Explain the Giant Impact Hypothesis
Theia collided with proto earth
flown fragments coalesced to form the moon
137
Photochemical Dissociation
(UV rays dissociate H2O into H2 & O2
138
stars become brighter as they age. The Sun has become 30% brighter; poses problem with ocean formation.
Faint Young Sun Paradox
139
Period of intense bombardment of meteorites,
comets, asteroids, and other rock fragments
Marks the boundary of Hadean and Archean.
Late Heavy Bombardment (4.1 Ga – 3.8 Ga)
140
postulates that Jovian planets underwent orbital migration and scattered objects from the asteroid belt and/or Kuiper Belt, into eccentrical orbits into the terrestrial planets.
Nice Model
141
could have introduced amino acids to early ear
Accretion of Bio-Elements (ABEL) bombardment
142
2nd oldest eon; 32.6% of geologic time
Archean Eon
143
The Archean eon began with ____ and ended with ____
LHP; Huronian Glaciation
144
Oldest Archean microcontinents
Trans Hudson Belt
145
intrusive rocks with typical granitic composition (quartz and feldspar) but containing only a small portion of potassium feldspar. Tonalite, trondhjemite, and granodiorite often occur together in geological records, indicating similar petrogenetic processes; major components of Archean Cratons
Tonalite–trondhjemite–granodiorite (TTG)
146
process of outward growth of continents as plates collide with island arcs and other plates.
Continental Accretion
147
supercontinent; oldest continent. but
less size than Australia
Vaalbara
148
supercontinent in 2.7 Ga.
Comprised of later Laurentia & Baltica, the
western Australia (Yilgarn Craton, which
contained the 4.4 Ga zircon crystals), and
the Kalahari.
Kenorland
149
The shield that evolved from kenorland
Baltic/Fennoscandian Shield
150
Orogeny precursur to Kenorland
Algoman / Kenoran Orogeny
151
Layered sedimentary formation created by
Cyanobacteria using sand & rocks to form
mineral microbial mats.
Stromatolites
152
Oldest undisputed stromatolites
3.0 Ga found in the
Barberton Greenstone Belt, S. Africa
153
Archaean Atmosphere
No Oxygen , mostly CO2 and Methane
154
water layer between oxygenated and anoxic layers
Redoxcline
155
chemical sedimentary rocks characterized by alternating layers of iron-rich minerals and chert that are generally interstratified with bimodal submarine volcanic rocks and/or sedimentary sequences in Archean greenstone belts.
Algoma-type banded iron formations (BIF)
156
are thickly bedded Proterozoic BIFs composed of chert and
hematite (due to oxidation by oxygen). Most significant, esp. as source of Iron.
Superior-type BIF
157
oldest known glaciation at 2.9 Ga(Mesoarchean) corresponding to the diamictites of the Pongola Supergroup
Pongola Glaciation
158
3 ice ages at the end of Archean at 2.5 Ga. This coincides with the Great
Oxygenation Event. Oxygen reacted with CO2 and methane,
reducing greenhouse effect lowering the temperature
resulting to the death of anaerobic organisms
Huronian / Makganyene Glaciation
159
3rd eon and last eon of the Precambrian; 42.65% of GT (longest eon).
Proterozoic Eon
160
The Proterozoic eon began with ____ and ended with ____
Started with the Great Oxygenation Event and the Huronian Glaciation ice ages and ended with the appearance of complex hard-shelled organisms (Cambrian Explosion).
161
Establishment of Earth’s magnetic field
3.5 Ga
162
Age of Orogeny
Proterozoic Eon
163
Age of Orogeny
Nuna/columbia
Rodinia
Pannotia
164
period of peak free atmospheric oxygen; and its duration
Great Oxygenation Event
Began in Siderian Period
and ended in Rhyacian Period
165
Single-celled eukaryotes appeared after
Great Oxygenation Event
166
is the evolutionary radiation of
animals at 575 Ma.
Avalon Explosion
167
Current eon in GT from 539 Ma, denoting the most evolution of multicellular life
Phanerozoic Eon
168
eras of Phanerozoic Eon and duration
•Paleozoic Era is the first era from 539 Ma – 251 Ma
• Mesozoic Era is the middle era from 251 Ma – 66 Ma
• Cenozoic Era is the current era from 66 Ma
169
• 6 continents in Paleozoic
Baltica, Gondwana, Laurentia, Kazakhstania, China,
and Siberia.
170
In Middle Ordovician, this orogeny formed along the eastern Laurentia
(due to subduction of Iapetus Plate; 1st pulse of Appalachian Mts; deposition of
Catskill and Queenstone Delta). Dominant deposits are Oolitic carbonates
Taconic Orogeny
171
in Silurian, Baltica+Avalonia collided with Laurentia, forming Laurasia and closing
the northern Iapetus Ocean, and initiating the
Caledonian Orogeny
172
In Devonian, this orogeny initiated (3rd pulse of Appalachian Mts) as the
southern Iapetus narrowed between Laurasia and Gondwana. Other orogenies
include Antler (Cordillera) and Ellesmere (N. margin of Laurentia)
Acadian Orogeny
173
the passageway connecting Paleo-Tethys and Panthalassa.
Rheic Ocean
174
In Permian, complete assembly of Pangaea as Laurasia & Gondwana merged
(_____________). Enormous single ocean is called _________
Ouachita Orogeny; Panthalassa
175
When did pangea begin to split
Triassic
176
is a continental body of water which is very large in area and is either completely surrounded by dry land or connected to an ocean by a river, strait or "arm of the sea".
Epeiric/Inland seas
177
The Cordilleran Mobile Belt was caused by
changing subduction angle of the Farallon Plate. This is
comprised of Nevadan Orogeny, Sevier Orogeny, and Laramide Orogeny
178
is a short interval of max temperature characterized by the highest global temperatures; release of methane hydrates
Paleocene-Eocene Thermal Maximum
179
First major transgression in North American craton;
Sauk Sequence
180
Widespread carbonate deposition overlying basal sandstone; record time of major reef building; its sea represented one of
the most complete flood in continent
Tippecanoe Sequence
181
Last complete sequence to cover North American craton; Caused by the Mid-Cretaceous superplume event.
Zuni Sequence
182
Sequences in the Paleozoic
Sauk, Tippecanoe, Kaskaskia, Absaroka, Zuni
183
sudden appearance of hard-shelled organisms and the rapid diversification of organism
Cambrian Explosion
184
Appearance of first jawless fishes (agnathans).
Paleozoic
185
First true coral reefs ; non vascular land plants
Ordivician
186
2nd largest mass extinction in terms of extinct genera
End-Ordovician Mass Extinction
187
First vascular land plant appeared in
Devonian; Cooksonia
188
Mass extinction caused by the closing of Iapetus Ocean and orogenic events
Frasnian-Fammenian
189
Important guide fossil for Pennsylvania-Permian
Fusulinids
190
Amphibians appeared in
Carboniferous
191
is the greatest mass extinction event ,Caused by deep-sea anoxia, increased CO2 levels, global warming, and widespread volcanism (Siberian Traps)
Permian-Triassic Mass Extinction
192
Age of Reptiles
Mesozoic
193
ancestors to modern fishes
Teleosts
194
Ancestors of birds
Archaeopteryx
195
extinction caused by major oceanic changes and Central Atlantic Magmatic
Province volcanism
• End-Triassic Mass Extinction
196
Non-avian dinosaurs went extinct. Caused by meteorite, Deccan Traps, and other factors.
Cretaceous – Paleogene Mass Extinction
197
Age of Mammals.
Cenozoic
198
was an important late Cenozoic paleozoogeographic biotic interchange event in which land and freshwater fauna migrated from North America to South America via Central America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents
Great American Biotic Interchange
199
Marks a break between endemic European fauna and mixed fauna with strong Asian
species; extinction of most European primates. Caused by global cooling and
oceanic overturn, meteorite impact in Late Eocene, and the major Antarctic
Glaciation
Eocene – Oligocene Extinction (Transition)
200
is the extinction of larger land mammals at
20,000 to 10,000 years ago caused by human hunting and overkill
Pleistocene Megafauna Extinction
201
Oldest known human hominin is
Sahelanthropus tchadensis
202
Members of Homo
include H. habilis (2.5 Ma), H. erectus (1.8 Ma), and
H. sapiens. Evolved species include H. neanderthalensis, Cro-Magnon,
H. floresiensis, H. luzonensis, H. denisova
203
Evolution of Primates
• Bipedalism in 10 Ma to 5.0 Ma
• Enlarged skull or brain case in 3.0 Ma to 2.0 Ma
• Stone tools at 2.6 Ma
• Wide geographical distribution at 2.0 Ma to 1.5 Ma
• Cultivation of fire at 1.5 Ma
• Art (cave paintings) at 35,000 years ago
