Introduction to Earth Sciences

What is Geology?Geology is the study of Earth and has traditionally been divided into two broad areas of interest:

1) Physical geology which concerns rocks and minerals and the processes as well as internal and external Earth-processes, and

2) Historical geology which examines the origin and evolution of Earths continents, oceans, atmosphere, and life.

Geology is a very broad and diverse discipline with many different specialties that draw on knowledge from related sciences such as astronomy, biology, physics, and chemistry.

How Does Geology Relate to the Human Experience?Nearly every aspect of geology has some economic or environmental relevance. From these we can trace many connections between geology and various aspects of our lives.

The struggle for control of natural resources such as oil, gas, gold, diamonds, etc., is a recurring theme in human history. Throughout history empires have risen and fallen on the distribution and exploitation of natural resources.

Natural features shaped by geologic processes serve as political boundaries and have shaped the tactics of military campaigns

EARTH HISTORYBig Bang theory: Universe has expanded from a primordial hot and dense initial condition at some finite time in the past and continues to expand to this day. The present available measurements suggest that the Big Bang occurred around 13.3 to 13.9billion years ago.

The current estimate is that the earth is 4.6 billion years old.

The history of Earth describes the most important events and fundamental stages in the development of planet Earth from its formation (4.6 by) ago to present day.

The division of Earth history into blocks of time distinguished by geologic and evolutionary events, ordered sequentially and arranged into Eons made up of Eras, which are in turn made up of Periods, which are in turn made up of Epochs.

Geologic Time Scale The hierarchical set of divisions in the history of earth is described by Geologic Time Scale.

Evolution of the Continents

Evolution of the ContinentsBreakup of PangaeaFossil Evidence in Gondwanaland

Principles & Laws of Relative Geological datingRelative dating: Putting geologic events into proper order (oldest to youngest), but without absolute ages (Using radioactive decay of element to determine the absolute ages of rocks). We use a number of principles and laws to do this.

Law of original horizontality: sedimentary units and lava flows are deposited horizontally.

Law of Superposition : The layer below is older than the layer above.

Principle of fossil succession: Life forms succeed one another in a definite and determinable order and therefore, a time period can be determined by its fossils.

Law of cross cutting relationship: A rock is younger than any rock across it cuts.

Fossils!

Trace

Mold

Cast

Amber

Imprint

Petrified

Some geologic features take millions of years to form

Others take seconds

Evolution of Life

Evolution of LifeAlthough the changes produced in a single generation are normally small, the accumulation of these differences over time can cause substantial changes in a population, a process that can result in the emergence of new species.

Similarities among species suggest that all known species descended from a common ancestor (or ancestral gene pool) through this process of gradual divergence.Evolution is change in the genetic material of a population of organisms through successive generations.

Evolution of Life & Atmosphere

Some major episodes in the history of life.

Evolution of Life (Contd.)

Evolution of Life (contd.)Pre Cambrian life (Before 550 My):

Single-celled life: Cyanobacteria (blue-green algae), Prokaryotes, Stromatolites

Metazoan Life (multicelled animals)Ediacara Fauna

Major occurrences in the world including those in India

Evolution of Life (contd.)Pre Cambrian life:

Evolutionary line Of Prokaryotes.

Paleozoic life (540 - 250 My ago)

Origin of vertebrates

Early Fishes

Early Tetrapods

Early Amniotes

Plant evolution

Land animals!Land plants!

End of the paleozoic era led to mass extinction!

The earth started getting larger life!

First part of paleozoic is called cambrian

Protists!

Sea animals!Sea plants!

Paleozoic life (Contd.)

Mesozoic Life (225 65 MY):Reptile: Dinosaurs flying reptiles Marine reptiles

Origin of birds

Origin of mammals Major invertebrate groups: e.g. Ammonites

Origin of flowering plants (angiosperms)

CENOZOIC LIFE (65 My Present): Origin of modern mammals Examples: whales, horses, humans

Ice ages and mammalian extinctions

Clock analogy for some key events in evolutionary history

Emergence of Humans

Emergence of HumansAfter hominids diverged from chimps and gorillas, evolution has followed a complex path

Numerous hominids species existed, some during the same time periodAll humans are the same species

First skull fossils that are identical to modern human skulls dates to 100,000 yr old

Our ancestors shared the Earth with NeanderthalsWent extinct 35,000 years ago

Brief Review of Evolution of Life

Mass ExtinctionAn extinction event (also known as: mass extinction; extinction-level event, ELE, or biotic crisis) is a sharp decrease in the diversity and abundance of macroscopic life.

They occur when the rate of extinction increases with respect to the rate of speciation.

The classical "Big Five" and other minor mass extinctions identified by Jack Sepkoski and David M.

These are End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous.Possible Causes:Major glaciations, Plate redistribution, Volcanic causes, Meteorite impact, Sea bed anoxia.

END OF SOLAR SYSTEM About 5 by yrs from NowIf Big Bang became accepted by the consensus of scientists & If Big Bang is true!!

Then the ultimate fate of the universe became a valid cosmological question.

It cannot last forever. Something unpleasant is bound to shatter this comfortable calm.

Our Sun will die, of course, may be about 5 byrs from now.

But things could get ugly long before that.

APPENDIX

GOALSTo understand the Earth. This includes surface rocks and structures, the oceans, inner structure, atmosphere, planetary geology

exploration and recovery of natural resources,

engineering stable structures (i.e. dams, tunnels, bridges, etc.)

Study of fossils

Earth Sciences

GeologyGeophysicsOceanographyAtmospheric Sciences

Introduction to Earth SciencesLearn about the Earth, its origin and evolution, and how human activities affect it.

Shape and Size of Earth

Shape and Size of Earth (contd.)To imagine the shape of the earth must have been difficult in early daysToday we all for granted that the Earth is nearly round and that it is not the centre of universe

Shape and Size of Earth (contd.)The earth is unique in shape

The mathematical euipotential surface which described the shape of the earth called Geoid

Shape and Size of our Earth (contd.)Equatorial radius = 6378 km

Polar radius = 6357 km

Volume = 1.083 x 1027 c.c.

Surface area = 5.1 x 1018 sq. cm

% surface area of oceans = 71%

% surface area of land = 29%

Average elevation of land = 623 m

Average depth of oceans = 3.8 km

Shape and Size of our Earth (contd.)Mass of earth = 5.976 x 1027 grams

Density = 5.517 grams / cc Mass of atmosphere = 5.1 x 1021 grams

Mass of oceans = 1.4 x 1024 grams

Mass of Crust = 2.5 x 1025 grams

Mass of mantle = 4.05 x 1027 grams

Mass of Core = 1.90 x 1027 grams

Gravity at equator = 978.032 cm/sec2

Earth's InteriorThe Earth, the Sun, and the rest of the solar system, was formed 4.54 billion years ago by accretion from a rotating disk of dust and gas.

The immense amount of heat energy released from gravitational energy and from the decay of radioactive elements melted the entire planet, and it is still cooling off today.

Denser materials like iron (Fe) sank into the core of the Earth, while lighter silicates (Si), other oxygen (O) compounds, and water rose near the surface.

Earth's Interior (contd.)The earth is divided into four main layers: the inner core, outer core, mantle, and crust.

The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S).

The inner core is under such extreme pressure that it remains solid.

Earth's Interior (contd.)

Earth's Interior (contd.)

Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds.

At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner.

Earth's Interior (contd.)The crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals.

Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes.

Geological Time (contd.)Absolute (Radiometric) Dating: This is done using igneous and metamorphic rocks.

Fossils are usually found in sedimentary rocksGeological Time (contd.)

Earth HistoryEON: Eons are the longest portions of geologic time.

Four major Eons are recognized: Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), Proterozoic Eon, Archean Eon and Hadean Eon. ERA: A period of time in which a new order of things prevails. The second-longest portions of geological time. Two or more Eras form an Eon, the largest division of geologic time.

PERIOD: Period is the basic unit of geological time in which a single type of rock system is formed.Two or more periods comprise a geological Era.

EPOCH: An epoch is a time division criteria based on specific physical and chemical characteristics in rock layers (lithography) indicative of the global environment, including tectonic activity (mountain building, continental drift, etc.) It also includes macroscopic and microscopic features and characteristics that are clear and distinct from other defining criteria.

Note that each eon, era, period or epoch represent different amount of time.

Earth History

The Cambrian radiation of animals

Major Events as basis for Geological Time

Mass ExtinctionAn extinction event (also known as: mass extinction; extinction-level event, ELE, or biotic crisis) is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation.

The classical "Big Five" mass extinctions identified by Jack Sepkoski and David M. These are End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous.

CretaceousTertiary extinction event (K-T extinction) - 65 Ma at the Cretaceous-Paleogene transition about 17% of all families and 50% of all genera went extinct. (75% species). It ended the reign of dinosaurs and opened the way for mammals and birds to become the dominant land vertebrates. In the seas it reduced the percentage of sessile animals to about 33%. The K-T extinction was rather uneven some groups of organisms became extinct, some suffered heavy losses and some appear to have been only minimally affected.

TriassicJurassic extinction event - 205 Ma at the Triassic-Jurassic transition about 20% of all marine families (55% genera) as well as most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, although it is known from Koolasuchus that the Temnospondyl lineage survived until the cretaceous in Australia. 23% of all families and 48% of all genera went extinct. PermianTriassic extinction event - 251 Ma at the Permian-Triassic transition, Earth's largest extinction killed 53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species (including plants, insects, and vertebrate animals). 57% of all families and 83% of all genera went extinct. The "Great Dying" had enormous evolutionary significance: on land it ended the dominance of mammal-like reptiles; the recovery of vertebrates took 30 million years but created the opportunity for archosaurs and then dinosaurs to become the dominant land vertebrates; in the seas the percentage of animals that were sessile dropped from 67% to 50%. The whole late Permian was a difficult time for at least marine life even before the "Great Dying".

Late Devonian extinction 360-375 Ma near the Devonian-Carboniferous transition at the end of the Frasnian Age in the later part(s) of the Devonian Period. A prolonged series of extinctions eliminated about 70% of all species. This extinction event lasted perhaps as long as 20 MY, and there is evidence for a series of extinction pulses within this period. 19% of all families of life and 50% of all genera went extinct. OrdovicianSilurian extinction event 440-450 Ma at the Ordovician-Silurian transition two events occurred, and together are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that went extinct. 27% of all families and 57% of all genera became extinct.

The general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers.

An ice age is a natural system. Within a long-term ice age, individual pulses of extra cold climate are termed "glacial periods" (or alternatively "glacials" or "glaciations"), and intermittent warm periods are called "interglacials".

There have been at least five major ice ages in the Earth's past.ICE AGES

ICE AGES2.4 to 2.1 by ago (Huronian): Rocks from the earliest well established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion) years ago during the early Proterozoic Eon.

850 to 630 My ago: The next well-documented ice age, and probably the most severe of the last billion years, occurred from 850 to 630 million years ago (Cryogenian period). ItIt may have produced a Snowball Earth in which glacial ice sheets reached the equator, possibly being ended by the accumulation of greenhouse gases such as CO2 produced by volcanoes.

460 to 430 MY ago: A minor ice age, the Andean-Saharan, occurred from 460 to 430 million years ago, during the Late Ordovician and the Silurian period. There were extensive polar ice caps at intervals from 350 to 260 million years ago in South Africa during the Carboniferous and early Permian Periods, associated with the Karoo Ice Age.

360 to 260 million years ago (The Karoo Ice Age): This ice age was largely the cause of the evolution of land plants with the onset of the Devonian period. The Earth during this time was covered with an immense degree of vegetation compared to earlier times, and this caused a long term increase in planetary oxygen levels and reduction of CO2 levels that resulted in this ice age.20 My ago: This began to grow some 20 My ago. The current ice age, the Pliocene-Quaternary glaciation, started about 2.58 million years ago during the late Pliocene when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacials (glacial advance) and interglacials (glacial retreat). The earth is currently in an interglacial, and the last glacial period ended about 10,000 years ago. All that remains of the continental ice sheets are the Greenland, Antarctic ice sheets and smaller glaciers such as on Baffin Island.

Causes of ice agesThe consensus is that several factors are important: atmospheric composition (the concentrations of carbon dioxide, methane); changes in the Earth's orbit around the Sun known as Milankovitch cycles (and possibly the Sun's orbit around the galaxy); the motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on the Earth's surface, which affect wind and ocean currents; variations in solar output; the orbital dynamics of the Earth-Moon system; and the impact of relatively large meteorites, and volcanism including eruptions of supervolcanoes.Some of these factors influence each other. For example, changes in Earth's atmospheric composition (especially the concentrations of greenhouse gases) may alter the climate, while climate change itself can change the atmospheric composition (for example by changing the rate at which weathering removes CO2).

ICE AGES

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