The fossil of one of the earliest birds, called The fossil of one of the earliest birds, called archaeopteryx, shows reptile-like features. It archaeopteryx, shows reptile-like features. It lived during the late Jurassic period, about 105 lived during the late Jurassic period, about 105 my ago.my ago. Fig. 4-CO, p.72

Earth Rocks, Earth History Earth Rocks, Earth History and Mass Extinctionsand Mass Extinctions

James Hutton, James Hutton, uniformitarimism and the uniformitarimism and the fossil record. fossil record.

Mass Extinctions (4.1)…large Mass Extinctions (4.1)…large ones 248 and 65 million ones 248 and 65 million years ago. What caused years ago. What caused them?them?

We will look at three We will look at three hypothesis for mass hypothesis for mass

extinctions next.extinctions next.

To rightTo right: the red line shows : the red line shows the number of families of the number of families of organisms has varied organisms has varied throughout time. What does throughout time. What does leftward shift mean?leftward shift mean?

Fig. 4-1, p.74

Fig. 4-1a, p.74

Fig. 4-1b, p.74

Fig. 4-1c, p.74

1. 1. Extraterrestrial ImpactsExtraterrestrial Impacts: Most scientists agree the Cretaceous : Most scientists agree the Cretaceous extinction was caused by a giant meteorite impact. Evidence is extinction was caused by a giant meteorite impact. Evidence is found in the Yucatan peninsula. It may have caused global cooling.found in the Yucatan peninsula. It may have caused global cooling.

Walter and Luis Alvarez (1977) found iridium-rich clay bed (rare on Walter and Luis Alvarez (1977) found iridium-rich clay bed (rare on Earth but abundant in meteorites). Suggested meteorite 10 km in Earth but abundant in meteorites). Suggested meteorite 10 km in diameter hit the Earth (with energy 10x that of our global nuclear diameter hit the Earth (with energy 10x that of our global nuclear arsenal). arsenal). Fig. 4-2, p.75

Evidence of Evidence of meteor meteor impact found impact found in Caribbean in Caribbean Sea.Sea.

Fig. 4-2a, p.75

The impact The impact would have would have pulverized pulverized the the meteorite meteorite and rocks of and rocks of the Earth’s the Earth’s crust crust creating a creating a thick, dark thick, dark cloud that cloud that caused the caused the Earth’s Earth’s surface to surface to freeze.freeze.

Fig. 4-2b, p.75

2. 2. Volcanic Eruptions:Volcanic Eruptions: can cause global can cause global warming and cooling…warming and cooling…how? 248 million years how? 248 million years ago massive flood ago massive flood basalts erupted in Siberia basalts erupted in Siberia (may have caused (may have caused Permian extinction). Permian extinction).

3. 3. Atmosphere-Ocean-Atmosphere-Ocean-Continent System Continent System Interactions:Interactions: supercontinent supercontinent assembled during assembled during Permian; no mixing from Permian; no mixing from currents, CO2 level rose currents, CO2 level rose in sea, temperatures fell in sea, temperatures fell (less greenhouse gas in (less greenhouse gas in atmosphere), sea level atmosphere), sea level fell, glaciers grew, fell, glaciers grew, oceans cooled at surface oceans cooled at surface and eventually sank, and eventually sank, releasing large amounts releasing large amounts of CO2 into atmosphere. of CO2 into atmosphere. Fig. 4-3, p.76

Fig. 4-3a, p.76

Fig. 4-3b, p.76

Geologic TimeGeologic Time

How old is the Earth?How old is the Earth? When did our earliest ancestors arrive?When did our earliest ancestors arrive?

Geologic time is deep time. Scientists measure Geologic time is deep time. Scientists measure time in two different ways: time in two different ways: RelativeRelative (the order (the order in which events occurred) and in which events occurred) and AbsoluteAbsolute (the (the order and how much time has passed since order and how much time has passed since they occurred).they occurred).

Fig. 4-3c, p.76

Relative Relative Time: The Time: The principle of principle of original original horizontalityhorizontality tells us that tells us that most most sedimentary sedimentary rocks are rocks are deposited in deposited in horizontal horizontal beds….beds….

If tilted….If tilted….

Fig. 4-5a, p.79

……we infer we infer that they that they were tilted were tilted after they after they were were depositeddeposited

……and…and…

Fig. 4-5b, p.79

……folded after folded after they formed, they formed, such as this such as this limestone limestone that formed that formed 500 million 500 million years ago in a years ago in a shallow sea. shallow sea. Four hundred Four hundred million years million years later, tectonic later, tectonic forces forces uplifted and uplifted and folded it in folded it in the Canadian the Canadian Rockies, Rockies, Alberta.Alberta.

Fig. 4-4, p.78

The principle of The principle of superpositionsuperposition states that in a states that in a sequence of sedimentary beds, the oldest bed sequence of sedimentary beds, the oldest bed (labeled 1) is at the bottom, and the youngest (labeled 1) is at the bottom, and the youngest (labeled 5) is on top.(labeled 5) is on top.

Imagine the beds were tilted vertically; how Imagine the beds were tilted vertically; how could you tell which was youngest?could you tell which was youngest?

Fig. 4-6, p.79

The The principle of principle of cross-cross-cutting cutting relationshiprelationshipss is shown is shown where this where this basalt dike basalt dike cuts across cuts across sandstone sandstone in the walls in the walls of the of the Grand Grand Canyon. Is Canyon. Is the dike the dike older or older or younger younger than the than the sandstone?sandstone?

Fig. 4-7, p.79

Three dikes cutting across sedimentary Three dikes cutting across sedimentary rocks. What are the age relationships?rocks. What are the age relationships?

Fig. 4-8, p.79

The The theory of evolutiontheory of evolution states that life forms have changed states that life forms have changed throughout geologic time. Fossils are remains/traces of throughout geologic time. Fossils are remains/traces of prehistoric life preserved in sedimentary rocks. prehistoric life preserved in sedimentary rocks.

What is the principle of What is the principle of faunal successionfaunal succession? How do fossils ? How do fossils show ancient environments (like corals found at the show ancient environments (like corals found at the summit of Mount Everest?)… summit of Mount Everest?)… Fig. 4-9, p.80

Gaps in the record: Unconformities and correlation…the Gaps in the record: Unconformities and correlation…the walls of the Grand Canyon show sedimentary rocks walls of the Grand Canyon show sedimentary rocks lying on igneous/metamorphic rocks (age ranges from 2 lying on igneous/metamorphic rocks (age ranges from 2 billion to 200 million years). billion to 200 million years). Fig. 4-10, p.80

A disconformity is created by uplift and A disconformity is created by uplift and erosion, followed by deposition of more erosion, followed by deposition of more sediment. The disconformity is a gap in sediment. The disconformity is a gap in the rock record. the rock record.

Fig. 4-11, p.81

Fig. 4-12, p.81

Angular Angular unconformity…unconformity…

Fig. 4-13, p.82

Fig. 4-13a, p.82

Fig. 4-13b, p.82

Fig. 4-13c, p.82

Fig. 4-13d, p.82

Fig. 4-14, p.82

The rock The rock record is full record is full of gaps in of gaps in any one any one place…so place…so must must correlate for correlate for a more a more complete complete record…record…correlation correlation includes includes time and time and lithologic.lithologic.

Fig. 4-15, p.83

For time correlation, use index fossils, fossil For time correlation, use index fossils, fossil assemblages and key beds. assemblages and key beds.

Fig. 4-17, p.84

Fig. 4-16, p.84

Fig. 4-16a, p.84

Fig. 4-16b, p.84

Fig. 4-16c, p.84

Absolute Geologic Absolute Geologic Time: geologists Time: geologists have found a have found a natural process natural process that occurs at a that occurs at a constant rate and constant rate and accumulates its accumulates its own record own record (unstable or (unstable or radioactive radioactive isotopes)… isotopes)…

Fig. 4-18, p.85

RadioactivRadioactive parent e parent decays to decays to daughterdaughter…the half-…the half-life is the life is the time time required required for half of for half of the parent the parent to decay to decay to to daughter.daughter.

Fig. 4-19, p.86

Table 4-1, p.87

The The geologic geologic time time chart. chart.

Fig. 4-20, p.89

Fig. 4-21, p.90

Fig. 4-22, p.90

Fig. 4-23, p.91

p.92