Evolution, Composition And Structure Of Earth Flashcards
(93 cards)
1
Q
What are the theories that are trying to explain the origin of the universe
A
-Big bang theory
-Nebula hypothesis
-James jeans’ tidal hypothesis
-Inter stellar dust hypothesis
-Creation theory
2
Q
What do you know about big bang theory
A
was postulated by Lemaitre Georges and Edwin Hubble 1920s
It states that 15b yrs ago a tremendous explosion (big bang*) occurred which started the expansion of the universe
At the point of this event all matter and energy of space were contained at one point. The explosion pushed matter and energy exploding in all directions. As the universe expanded matter collected into clouds that began to condense and rotate, forming the forerunner of galaxies including the milky way
3
Q
What are planetesimals or protoplanets
A
This are the bodies form when sun, gas and dust within the disk collid and aggregated into small grains of several hundred km
4
Q
What are the critiques of the big bang theory
A
*it propounded that the universe emerged from the enormous atomic nuclear, however it remains silent on how, and through which mechanisms and processes the atomic nuclear was composed, evolved and developed prior to its accumulation and explosion
*based on the theory it appears that all the galaxies emerged at the same time thus having the same age. However, the current astronomic researchers found that while other galaxies are too old, there are many young galaxies around and far from the earth
5
Q
What do you know about the nebular hypothesis
A
Proposed by philosopher Immanuel Kant (1755), was one of the first scientific theories explaining the solar system’s
Also known as Kent’s gaseous hypothesis
6
Q
Point out the key breakdowns in explaining the nebular hypothesis
A
-Nebula origin
-Gravitational collapse
-Formation of bodies
7
Q
What is the Nebula origin
A
Kant suggested the solar system began as a rotating, gaseous nebula (cloud) of hot, chaotic matter.
8
Q
Explain the gravitational collapse stage of the nebular hypothesis
A
Over time, gravity caused the nebula to cool, contract, and spin faster, flattening into a disk
9
Q
Explain the formation of bodies in the nebular hypothesis
A
- Denser regions in the disk clumped together to form the Sun at the center.
- Smaller clumps in the outer disk coalesced into planets, with inner planets being rocky (due to heat) and outer planets icy/gaseous (due to cold).
10
Q
What are the critiques on Kent’s gaseous hypothesis
A
- large amount of heat cannot
be generated due to the collision of cold particles of primordial matter as claimed
by Kant - mutual collision of particles
cannot generate motion in the primordial matter and the random motion of the particles cannot generate circular motion
in the primordial matter - the angular velocity of rotary speed of the nebular cannot increase due to increase
in size of the nebular as assumed by Kant
11
Q
What do you know about laplace’s nebular hypothesis
A
Proposed in 1796 that the solar system formed from a rotating, flattened cloud of hot gas (nebula).
12
Q
Mention the stages of universe formation by using laplace’s point of view
A
-Initial stage (nebula stage)
-Gravitational contraction
-Conservation of angular momentum
-Centrifugal ejection of rings
-Planet formation
-Sun formation
-Moon formation
13
Q
Elaborate on the conservation of angular momentum
A
- As the nebula contracts, it spins faster (like a figure skater pulling in their arms).
- This flattens the nebula into a disk perpendicular to its axis of rotation.
14
Q
Explain the centrifugal ejection of the rings
A
- At the outer edge of the spinning disk, centrifugal force balances gravity, causing the nebula to shed concentric rings of material from its equator.
- This process repeats as contraction continues, leaving multiple rings at varying distances
15
Q
Explain Planet formation
A
- Each ring condenses and cools further, with particles colliding and accreting into a protoplanet at the ring’s center.
- Over time, these protoplanets sweep up remaining material, becoming the planets.
16
Q
Explain sun formation
A
The dense, central core of the nebula becomes the protosun, eventually igniting nuclear fusion to become the Sun.
17
Q
Explain moon formation
A
Laplace suggested a similar process: planets ejected their own rings during contraction, forming moons around them
18
Q
A
19
Q
What are the critiques of laplace’s nebular hypothesis
A
- Where did the heat and motion in that nebula come from?
*What was the reason
behind the formation of certain fixed number of planets from the irregular ring
*Why did only 9 rings come
out from the irregular ring detached from the nebula?
*Why there were no more or less than 9 rings?
*If Laplace’s hypothesis is
accepted that the planets were formed 7 from the nebula, then the planets must have been in liquid state in their initial stage. But the planets in liquid state cannot rotate and revolve around the sun on rings
20
Q
What do you know about James jeans’ tidal hypothesis
A
The tidal hypothesis (proposed by James Jeans and Harold Jeffreys, early 20th century) suggests the solar system formed due to a close encounter between the Sun and another star
21
Q
Mention the key steps and content in the tidal hypothesis
A
-Stellar encounter
-Tidal ejection
-Filament condensation
-Orbital alignment
-Differentiation
22
Q
Explain the Stellar encounter
A
A passing star gravitationally interacts with the young Sun, pulling material from it through extreme tidal forces.
23
Q
Explain tidal ejection
A
The star’s gravity stretches the Sun’s outer layers, ejecting a hot, cigar-shaped filament of gas and dust
24
Q
Explain Filament condensation
A
- The ejected material cools and fragments into planetary blobs (protoplanets) along the filament.
- These blobs accrete leftover material to form planets.
25
Explain Orbital alignment
Planets inherit motion from the Sun’s rotation and the passing star’s trajectory, explaining their **near-circular orbits** in the same plane
26
Explain differentiation
- Inner planets are rocky (material cooled quickly near the Sun). Outer planets retain gases and ices (cooler conditions farther out).
27
What are the criticism of tidal hypothesis
*James Jeans did not explain the destiny of the intruding star
*the tidal hypothesis fails to
explain the real distances between the sun and the planets in our present solar system
28
What do you know about inter Stellar dust hypothesis
Was proposed by Otto Schmidt 1943
It emphasizes the critical role of **dust grains** in the interstellar medium (ISM) as foundational elements in star and planet formation
29
What are the key steps and content in the interstellar dust hypothesis
-Composition of interstellar dust
-Cooling & Cloud Collapse
-Shielding & Molecule Formation
-Planetesimal Formation
-Role in Star Formation
30
Elaborate the Composition of interstellar dust
Tiny solid particles (0.1–1 µm) made of **silicates, carbon compounds, and ices**, mixed with gas (mostly H and He) in molecular clouds
31
Elaborate on the Cooling & Cloud Collapse in interstellar
- Dust **radiates heat** as the cloud contracts, allowing the gas to cool and lose pressure.
- This enables gravitational collapse of the molecular cloud, forming dense **protostellar cores**
32
Elaborate on the Shielding & Molecule Formation in interstellar hypothesis
- Dust blocks UV radiation, shielding molecules (e.g., H₂, CO) from destruction.
- Acts as a **catalyst**, providing surfaces for gas molecules to stick and form icy mantles
33
Elaborate on the Planetesimal Formation in interstellar hypothesis
- Dust grains collide and **coalesce** into larger aggregates (pebbles, rocks).
- In protoplanetary disks, these aggregates grow into **planetesimals** (kilometer-sized bodies), the building blocks of planets
34
Elaborate on the Role in Star Formation step in interstellar hypothesis
Dust contributes to **opacity** in disks, regulating temperature and enabling material to accrete onto the protostar
35
What are the critiques of the interstellar hypothesis
*The hypothesis has been criticized that gravitational force of the primitive sun was incapable of capturing dark matter scattered in the universe
*According to some astrophysicists ‘meteorites and asteroids were formed as a result of the disintegration of some planets and not the planets were formed out of meteorites and asteroids
*Until now no trace of remnants of dark matter could be discovered either in the archaeological drilling on the earth’s surface or on any planet
36
What do you know of creation theory or theological theory
It's the religious theory of the universe
37
How far is the earth from the sun
150 million kilometers away
38
What is the shape of the earth
*geoid*, spheroid or obliterated sphere
39
What are the theories that elaborate on the earth’s shape
-Plato and Aristotle's theory of natural place
-Heliocentric theory
-Centripetal theory
-Geocentric theory
40
What do you know about Plato and Aristotle's theory of natural place
**Plato**: Elements (earth, water, air, fire) inherently seek their "natural realm" in a geometric, ordered cosmos. Earth sinks; fire rises. Motion reflects a divine, rational structure (e.g., *Timaeus*).
**Aristotle**: Each element moves toward its *natural place* based on intrinsic qualities:
- **Heavy** (earth, water) → Downward (center of the universe).
- **Light** (air, fire) → Upward (periphery).
This creates a layered cosmos (*On the Heavens*).
41
What do you know about Heliocentric theory
It was put forward by Nicolaus Copernicus in 16th Century. The theory stated that the Earth was spherical in shape and it is one of the planets revolving the Sun. The theory considered the Sun to be the centre of the solar system and perhaps the universe.
Also, he believed that the bodies
like planets, comets and asteroids
revolved around it.
42
What do you know Centripetal theory
The theory was put forward by Sir Isaac Newton who used Mathematical evidence
to determine shape of the Earth.
He believed that the Earth is wider along the equator and flattens along the poles. According to Sir Isaac, bulging along the equator is due to rotation and centrifugal forces which overcome the gravity hence pulling of materials away from the centre. This contribute to the bulging nature of the Earth along the equator
43
What do you know about Geocentric theory
Proposed by Claudius Plotemy
He said that the Earth was spherical in shape. He believed that the Earth was the centre of the universe and Stationary. However, the theory was partially disproved by modern science as it was realized that the Earth and other bodies like star, sun,moon and other planets were not Stationary
44
What are the evidences that prove the sphericity of the earth
*aerial photograph
*circumnavigation
*lunar eclipse
*surveying with ranging poles on level ground
*ship's visibility
*sunrise and sunset
*measuring weight using a spring balance
*the Earth's curved horizon
45
What are the causes of oblateness of the earth
*High speed of rotation along the Equator
*Low speed of rotation at the poles:
46
What are the evidences that prove the oblate spheroid of the Earth
*inequality of circumference and diameters between equator and poles
*measurement of latitude and recent satellite image data
*Larger equatorial diameter of 12762 km results into larger equatorial circumference of 40085 km while smaller polar diameter results into small circumference of 39955 km
*Variations in the measurements
of latitude are caused by the difference in the curvature between the equatorial and polar areas.
*Recent satellite data of the Earth suggest that the southern hemisphere is relatively smaller than the northern hemisphere which also proves that the planet earth is not a perfect sphere
47
48
What are the five components or parts of the Earth
- Atmosphere
- Hydrospher
- Biosphere
- Geospher
- Cryosphere
49
What is Atmosphere
The word atmosphere is the combination of two Greek words; ‘atmos’ meaning “vapour” and ‘sphaira’ meaning “sphere”
It stands like an envelope of transparent odourless gases held on the Earth by gravitational attraction. It extends up from the earth surface for several hundreds of kilometres
50
What is Biosphere
a life supporting layer which
surrounds the Earth and makes plant and animal life possible without any protective device
51
What is geosphere
it includes the rocks and minerals on Earth from the molten rock and heavy metals in the deep interior of the planet to the sand on beaches and peaks of mountain. Thus, it includes all minerals, rocks and soils.
52
What is Hydrosphere
is the sphere that covers total amount of water on a planet Earth. It includes water available on the surface of the Earth, underground and in the air
53
What does Cryosphere
Is an all-encompassing term for those portions of the earth's surface where water is in solid form, including sea ice, ice sheet, lake ice, river ice, snow cover, glaciers, ice caps and frozen grounds
54
What are the external structure of the earth
- atmosphere
- hydrosphere
- cryosphere
- biosphere
55
What are the atmospheric compositions
The atmosphere is constituted of both living and non-living components. The living organisms include bacteria in which some are harmful to human life. Non-living components include gaseous and non-gaseous components such as dusts and particles
56
What gases is the atmosphere composed of
- Nitrogen 78%
- Oxygen 21%
- Carbon dioxide 0.03%
- Argon 0.93%
- Water vapor 0.20 to 4%
- Trace gases
57
What are the layers of atmosphere
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exospere
58
What do you know about Troposphere
This is the bottom immediate layer from the earth’s surface. It starts at the earth’s surface and extends to
an average of 12 kilometers
high being 8 kilometres at the
poles and 17 kilometers at the
equator
59
What are the features of Troposphere
- *Temperature decreases with increase I altitude by 0.6°c for every 100m or 6.5°c for every 1 km*
- *Pressure falls with altitude due to decrease of gravity *
- *The air pressure at the top of the Troposphere is only 10% of that at sea level*
- *The troposphere is where all weather takes place*
60
What is tropopause
Is a thin buffer zone between the troposphere and the next layer called the tropopause. The tropopause lies above the troposphere. It extends from 12
km to 20 km
61
What are the roles of troposphere on life
- *Providing oxygen and hydrogen and carbon dioxide which is essential for photosynthesis*
- *It provides water vapour which
regulates temperature by preventing the outgoing radiation from the sun*
62
What are the features of Stratosphere
- *Steady increase in temperature caused by concentration of ozone (O3) which absorbs ultraviolet radiation from the Sun*
- *Air is dry and pressure continues to fall with altitude*
- *It contains 90% ozone layer and and it's approximately 16-50km above earth surface*
- *It has stratopause which separates Stratosphere from the next layer*
- *Temperature increases with the increase in height*
63
What is Stratosphere
This is the layer above the tropopause. It extends to about 50 km.
64
What do you know about mesosphere
The mesosphere is a layer above
the stratopause. It extends from
52km to 80 km above the surface
65
Mention the features of Mesosphere
- *temperature decreases rapidly with increasing height*
- *It has no water vapour, dust and clouds to absorb incoming radiation*
- *It has the lowest temperature which drops to -90°c*
- *It has high concentrations of ion and metal atoms*
- *Its the layer where shooting stars can be observed*
66
What are the benefits of Mesosphere
- *Mesosphere can be seen as a
protective layer of the earth’s
surface because meteorites of
various sizes are burn up in this
layer*
- *The mesosphere protects us
from solar radiation with varying
wavelengths*
67
What do you know about Thermosphere
Thermosphere broadly corresponds with the ionosphere. This layer lies above mesopause extending from 80 km into space. In this layer temperature ranges between 1 0000C and 1 5000C. However, it cannot be felt because air molecules are far apart almost zero amount of air density and almost without existence of gravity
68
What are the gases found in the thermosphere
Helium, atomic Nitrogen and atomic oxygen
69
What are the advantages of Thermosphere
- *The thermosphere contributes to the protection of the Earth as it absorbs x-rays and extreme ultraviolet radiation*
- *it enables space exploration and easy communication*
- *It absorbs the sun’s energy and
creates moderate temperature*
70
What do you know about exosphere
This is the highest and top layer of the earth’s atmosphere. It starts at 500km high and marks the edge of space. It is the earth's first line of defense against harmful rays and to come into contact and protect the Earth from meteors, asteroids and cosmic rays
71
What is the importance of atmosphere in life
- *It acts as a huge blanket, keeping the earth warmer than it would be without the atmosphere*
- *The atmosphere protects living things on Earth from the sun’s harmful ultraviolet radiation*
- *It provides oxygen for humans and animals to breath, and carbon dioxide for plants*
- *Through the hydrological cycle,
plants and animals receive the water needed to survive*
- *Atmosphere protects us from objects coming towards the earth from outer space*
- *The atmosphere protects us from space junk that would do damage to us, to our homes, and to the Earth itself*
72
What is the major setting of the earth's hydrological cycle
Hydrosphere
73
What is the narrow zone of the Earth of about 10km In which life forms exist
Biosphere
74
What are the three basic components of the biosphere
Abiotic, biotic and energy
75
What do you know about internal structure of the earth
The internal structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and geological properties
76
What are the two ways which layers of the internal structure of the earth be defined
Chemical and mechanical or geographical properties
77
What are the further categories of mechanical properties
- Lithosphere
- Asthenosphere
- Mesopheric mantle
- Outer core
- Inner core
78
What are the further categories of chemically properties
- Crust
- Mantle
- Core
79
What do you know about the crust
The crust ranges from 5-70 km (3-44 miles) depth and is the outermost thin layer of the earth
80
Mention the two kinds of crust
- Continental crust or felsic or SIAL(*silicate and aluminium*)
- Oceanic crust or mafic or SIMA(*silicate and magnesium*)
81
What is Conrad discontinuity
Is the layer that separates the SIAL and SIMA
82
What is the mohorovicic discontinuity or moho
Is the boundary between the crust and mantle
83
What does the upper mantle together with the crust constitutes
Lithosphere
84
What do you know about the mantle
It's the thickest layer of the earth also known as mesosphere. It extends 2890km where temperature may reach 5000°c with an average density of about 3.3g/cm3
*Its time layer of semi-molten materials acting as the center of isostatic adjustment known as **Asthenosphere** *
85
What is Gutenberg discontinuity
Is the layer that separates the mantle from the core
86
What do you know about the core
This is the innermost part of the earth which is also known as *barysphere*. It is made up of iron and nickel. It's size is that of Mars which is about 6900km thick
87
What are the two compositions of the core
Inner core which is solid and outer core which Is in molten state
88
What is Lehman discontinuity
Is the boundary between the inner core and the outer core
89
What are the factors that determine the strength of the gravity
- *The distance from the centre of the earth*
- *The spin of the earth on it's axis*
*The nearby sources of gravity variations*
90
What is gravity or gravitation
Gravity or gravitation is a natural phenomenon by which all things with energy are brought towards (or gravitate towards) one another, including stars, planets, galaxies and even light and sub-atomic particles
91
92
What are the benefits of gravity
- *Earth, gravity gives weight to physical objects and causes the tides*.
- *It is the glue that holds together entire galaxies*
- *It keeps planets in orbit*
- *It makes possible to use man made satellites and to go to and return from moon*
- *It makes planets habitable by trapping gases and liquids in the atmosphere*
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