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LEC.103 > Lecture 2 - Evidence for past Climates 1 > Flashcards

Lecture 2 - Evidence for past Climates 1 Flashcards

1
Q

What principles does Stratigraphy rely on?

A

Principle of original horizontality

Principle of superposition

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2
Q

What is the principle of original horizontality?

A

sediments are deposited under the influence of gravity as nearly horizontal beds. If we find folded or faulted strata, we know that the beds were deformed by tectonic forces after the sediments were deposited.

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3
Q

What is the principle of superposition?

A

each layer of an undeformed sedimentary sequence is younger than the one beneath it and older than the one above it. A chronologically ordered set of strata is known as a stratigraphic succession .

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4
Q

What are the problems with stratigraphy?

A

Almost always gaps in a region’s stratigraphic succession, indicating time intervals that had gone entirely unrecorded
It was difficult to determine the relative ages of two formations that were widely separated in space (physical space)

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5
Q

What is an unconformity and what does it represent?

A

The surface between two beds that were laid down with a time gap between them
Represents the passage of time, just like a sedimentary sequence

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6
Q

What is a disconformity?

A

Unconformity at which an upper sedimentary sequence overlies an erosional surface developed on an undeformed, still-horizontal lower sedimentary sequence.

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7
Q

When is a disconformity formed?

A

When sea level drops or during broad tectonic uplifts

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8
Q

What is a non-conformity?

A

An unconformity at which the upper sedimentary beds overlie metamorphic or igneous rocks

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9
Q

What is an angular unconformity?

A

Unconformity in which upper beds overlie lower beds folded by tectonic processes, and then eroded to a more or less even plane

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10
Q

What is the principle of faunal succession?

A

Sedimentary strata in an outcrop contain fossils in a definite sequence. The same sequence can be found in other locations, so strata’s in different locations can be matched

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11
Q

When are isotopic dating methods possible

A

If a measurable amount of parent atoms remain in the sample being dated

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12
Q

What do we use carbon-14 to date?

A

bone, shell, wood and other organic material in sediments less than a few tens of thousands of years old

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13
Q

What do we use for dating the oldest rocks?

A

Uranium 238

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14
Q

What is the most mobile and changing part of the Climate System?

A

The atmosphere

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15
Q

What does the hydrosphere comprise?

A

All liquid water on, over and under the Earth’s surface

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16
Q

What is the distribution of the Hydrosphere?

A

99% is in oceans, 1% is in lakes, streams and groundwater

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17
Q

Which is more efficient at heat transfer, the atmosphere or the hydrosphere?

A

Hydrosphere

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18
Q

What part of the lithosphere is most important to the Climate System?

A

The land surface

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19
Q

What % of the Earth’s total surface area is made up of the land surface?

A

30%

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20
Q

How much ice does the cryosphere contain?

A

33 million cubic kilometres

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21
Q

What is the biosphere comprised of?

A

All organisms living on and under Earth’s surface, in the atmosphere and in water

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22
Q

What % of incoming solar energy is used by plants for photosynthesis?

A

<0.1%

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23
Q

Where does all the energy driving the climate system come from?

A

The sun

24
Q

What must the earth maintain?

A

A radiation balance

25
Q

What is a radiation balance?

A

An equilibrium between incoming and outgoing radiant energy

26
Q

What is El Nino (and the counter)

A

El Nino – Warming of Eastern Pacific Ocean every 3-7 years

La Nina – the complementary cooling event

27
Q

What causes El Nino?

A

Trade winds weaken, cutting off typical cold water upwelling in Peru and equalizing water temperatures across the tropical Pacific

28
Q

What causes La Nina?

A

Trade winds strengthen, enhancing the temperature difference between the Eastern and Western Pacific

29
Q

How does a glacial cycle start and end?

A

With a gradual decline in temperature from a warm interglacial period to a cold glacial period. As climate cools, water transferred from hydrosphere to cryosphere. More ice means more reflected solar energy – temperatures falls further. Ends with an abrupt rise in temperature, after which things return to normal

30
Q

What is a Milankovitch cycle?

A

Periodic variations in the amount of radiation the Earth receives from the sun

31
Q

What factors affect the Milankovitch cycle?

A

Shape of the Earth’s orbit around the sun
The angle or tilt of the Earth’s axis
The Earth’s axis of rotation

32
Q

How much have Carbon Dioxide levels risen in the last 200 years?

A

50%

33
Q

What are Geochemical cycles?

A

The flow, or flux, of chemicals from one component of the Earth system to another

34
Q

What main reservoirs does carbon cycle between?

A

the atmosphere, the oceans, the land surface and the deeper lithosphere

35
Q

Average carbon flux between the Atmosphere and Ocean?

A

80 Giga Tonnes per Year

36
Q

What does carbon flux between atmosphere and oceans depend on?

A

air and sea temperatures, composition of seawater and wind velocity

37
Q

Average carbon flux between the Atmosphere and Biosphere?

A

Greatest carbon flux - 120 Giga Tonnes a year

38
Q

How is carbon exchanged between the atmosphere and biosphere?

A

photosynthesis, respiration and decomposition

39
Q

What is the aims of tools for reconstruction of past climates?

A

To give a date or give the environmental information, or both.

40
Q

What do we need to interpret rocks?

A

To understand present day processes
Methods of determining ages of rocks, landforms and fossils
A geologic calendar

41
Q

What techniques do we use for relative dating?

A

Stratigraphy and palaeontology

42
Q

What does relative dating tell us?

A

which rocks are youngest and oldest, not exact dates

43
Q

What does absolute dating give us?

A

The absolute date in thousands or millions of years, of the rock.

44
Q

How can we use isotopes for absolute dating?

A

We can measure the ratio of parent to daughter atoms in a rock sample to determine the time since the isotopes were locked into the minerals (crystallization from melt, or cooling after metamorphism)

45
Q

What is the lab procedure for absolute dating using isotopes?

A

Uses a mass spectrometer

  1. Count the daughter element atoms
  2. Know the decay rate
  3. Calculate the time when there no daughters (only parents)
  4. Tells us the time of rock formation. If the rock gives us climate information we then know what the climate was like at this point in time
46
Q

What does Uranium 238 decay into?

A

Lead 206

47
Q

Is there ‘common lead’ at the start for zircon?

A

No, it rejects it during it’s growth

48
Q

What is the half-life of carbon

A

5730 years

49
Q

Half-life definition

A

The time for one half of the original number of radioactive atoms to decay

50
Q

What discoveries have we made form relative and absolute dating?

A

The age of the Earth
The Earth has been shown to have been repeatedly shaped by environmental processes and systems (e.g. Ice ages) that operate today

51
Q

What is a geologic calendar/timescale?

A

a chronology of events on Earth based on obtaining ages of past events

52
Q

How do we obtain the ages of past events for geologic calendars?

A

(1) relative dating and (2) absolute dating (e.g. radiometric/isotopic dating) of rocks, sediments, fossils and landforms.

53
Q

What % of the Earth’s existence does the Pre-cambrian era span?

A

80%

54
Q

Why do we not know much about the Pre-Cambrian Era?

A

the record is more fragmentary, rocks are less exposed and reheated so earlier evidence is removed

55
Q

What happened in the last 20% of Earth’s history?

A

Explosion of life

56
Q

What did the pre-cambrian era not have?

A

Visible life

57
Q

Genera definition

A

Living and fossil organisms

LEC.103 (5 decks)

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