History of Earth

Question 1

Geology?

Answer 1

Study of Earth

Question 2

3 aspects of Earth’s geology which are important:

Answer 2

1. Volcanism (releases gases that were trapped in Earth’s interior as planet formed - also releases heat & creates chemical environments that almost certainly contributed to origin of life on planet)
2. Plate tectonics (responsible for long-term climate stability that has allowed life to thrive)
3. Magnetic field (shields atmosphere from energetic particles of solar wind)

Question 3

Fossils?

Answer 3

Relics of organisms that lived and died long ago.

Question 4

Geological record?

Answer 4

Rocks and fossils through which we can see history.

Question 5

3 types of rock?

Answer 5

Igneous rock (made from molten rock that cooled and solidified)
Metamorphic rock (structurally or chemically transformed by high pressure or heat that was not high enough to melt it)
Sedimentary rock (made by gradual compression of sediments, such as salt and silt at bottom of oceans)

Question 6

Basalt?

Answer 6

Igneous rock that is commonly produced by undersea volcanoes and rich in iron & magnesium-based minerals

Question 7

Granite?

Answer 7

Lighter in colour & less dense than basalt. Igneous rock common in mountain ranges.

Question 8

Strata?

Answer 8

Sedimentary rock marked by distinct layers.

Question 9

Why are the layers of strata important?

Answer 9

Allows geologists to determine relative ages of rocks and fossils.

Question 10

Mineral

Answer 10

Crystal of particular chemical composition and structure.

Question 11

What do rocks tell us and what do minerals tell us?

Answer 11

Rocks = how it’s made
Minerals = what it’s made of

Question 12

3 types of analysis important in reconstructing rock’s history

Answer 12

Mineralogical analysis (identifying minerals)
Chemical analysis (elemental or molecular composition)
Isotopic analysis (ratio of different isotopes.

Question 13

Why is isotopic analysis particularly illuminating?

Answer 13

Measurements show it exists in particular ratios in nature - if something has more than normal, then we know that something must have happened to enrich it.

Question 14

Radioactive?

Answer 14

Isotopes with nuclei which are unstable. Thus, they can undergo spontaneous change or radioactive decay.

Question 15

Radiometric dating? Why are radioactive isotopes useful?

Answer 15

Method which relies on measurement of an object’s proportions of various atoms and isotopes. Most reliable method for measuring age - means ratios of radioactive isotopes serve as natural clocks that can allow us to learn precisely when a rock formed.

Question 16

How do we term a nucleus that undergoes decay?

Answer 16

Original nucleus = parent nucleus
Changed nucleus = daughter nucleus

Question 17

Decay

Answer 17

Number of protons or neutrons change because an element is unstable, and it changes into different element.

Question 18

Alpha decay

Answer 18

Large nucleus ejects helium nucleus

Question 19

Why do fossils become rarer as we look deeper into geological past?

Answer 19

• Fossils can suffer same fates as rocks
• Large plants and animals, which are discovered more easily, are relatively recent arrivals.

Question 20

What are the 4 eons in order?

Answer 20

Hadean
Archean
Proterozoic
Phanerozoic

Question 21

3 eras within phanerozoic?

Answer 21

Paleozoic
Mesozoic
Cenozoic

Question 22

How do we know age of Earth?

Answer 22

• oldest known rock date to about 4.03 bln years ago.
• study of tiny mineral grains of zircons which show us 4.4blon years
  Moon rocks help estimate: older than 4.4 bln years
• Set maximum by studying meteorites, which have chemical structure that suggest they were firtst pieces to condense and these are about the same age, suggesting represent material from beginning of solar system - date to 4.57 bln years ago.

Question 23

Differentiation

Answer 23

Process in which materials separate by density - this led to a dense core and a rocky mantle, as well as a crust on Earth.

Question 24

Outgassing

Answer 24

Process fo releasing gases trapped in planetary interior in atmosphere.

Question 25

Lithosphere

Answer 25

Layer of cooler, more rigid rock that sits above warmer, softer mantle rock below. Includes crust & upper portion of mantle, extending to depth of about 100 kilometers.

Question 26

Seafloor crust

Answer 26

Relative dense, thin, young crust found on Earth’s seafloors, composed largely of the igenous rock called basalt.

Question 27

Continental crust

Answer 27

Thicker, lower-density crust that makes up Earth’s continennts. Made when remaining seafloor crust allows lower-density rock to separate, typically consists of granite: continental crust ranges in age from very young to about 4.0 bln years ago.

Question 28

Plate tectonics

Answer 28

Geological process in which lithospheric plates move around surface of Earth; acts like a conveyor belt, with new seafloor crust erupting and spreading outward from mid-ocean ridges and then being recycled back into mantle by subduction at ocean trenches. Also explains continental drift, because plates carry continents with them as they move.

Question 29

Ice ages

Answer 29

Periods of time during which Earth becomes unusually cold, so water from oceans freezes out as ice and covers substantial portion of continents.

Question 30

Snowball Earth

Answer 30

Periods of extreme ice ages that may have occurred several times before about 580 million years ago.

Question 31

Convection?

Answer 31

Hot material expands and rises wihile cooler material contracts and falls - takes so slow that a rock needs 100mln years to travel from base to top.

Question 32

Differentiation

Answer 32

Materials separate according to their density.

Question 33

3 main sources of heat that caused rock to melt?

Answer 33

Impacts of accretion created heat that melted outer layers;
Gravitational potential energy was converted into thermal energy that added further heat
Heat is continually released by radioactive decay of elements

Question 34

3 factors that determined cooling of worlds?

Answer 34

Size & ongoing heat deposition (if it has internal heat source)

Question 35

Subduction

Answer 35

A seafloor plate meets continental plate - the continental rock is less dense so the entire surface can be pulled downward to form a deep ocean trench. The seafloor crust thus gets recycled.

Question 36

Boundary faults?

Answer 36

Places where plates slip sideways relative to each other. This can cause earthquakes.

Question 37

Why is plate tectonics unique to Earth among terrestrial world?

Answer 37

Other planets have cooled down.
Venus high surface temperature and drying of rock has resisted fracturing that occurred on Earth.

Question 38

In what 3 majro ways can gas later be lost in space?

Answer 38

1. Thermal escape: gas molecules sometimes move fast enough that they may exceed their world’s escape velocity.
2. Impacts can blast atmospheric gas into sapce.
3. Solar wind stripping: particles from solar wind sweep atmospheric gas particles into space.