The Cenozoic Earth

Question 1

What are the general trends in the global temperature and sea level through the Cenozoic?

Answer 1

Transition from a warm, high-sea-level world to a cooler, glaciated planet with lower sea levels and episodic fluctuations.

Question 2

What were the climatic conditions during the Early Eocene climatic optimum? What caused this warming trend?

Answer 2

Global temperatures 10–12°C warmer than today and ice-free poles, resulting in tropical to subtropical climates extending to high latitudes.
-elevated greenhouse gas levels, released by volcanic activity
-possibly the release of methane hydrates
-breakup of continents also altered ocean circulation, reducing heat transfer to polar regions

Question 3

What ocean circulation patterns existed in the Palaeocene/Eocence and why?

Answer 3

Weak thermohaline circulation and enhanced equatorial currents. The breakup of continents altered ocean gateways

Question 4

What are hypothermals?

Answer 4

Short-lived, extreme warming events in Earth’s history, typically lasting thousands to tens of thousands of years

Question 5

What is PETM and what is thought to have triggered it?

Answer 5

Paleocene–Eocene Thermal Maximum (56Ma), is a hypothermal caused by methane hydrate release, volcanic activity and carbon ccyel disruptions

Question 6

How did deep water ocean circulation patterns change in the mid Eocene? Why?

Answer 6

From warm, sluggish, and stratified waters to a more active thermohaline circulation. Driven by the onset of polar cooling and the first significant formation of Antarctic ice sheets (40Ma), caused by declining CO₂ and opening of ocean gateways

Question 7

What is the circum-Antarctic ocean current? When did it initiate? What effect did it have on global temperature? How?

Answer 7

The circum-Antarctic ocean current is the largest ocean current, flowing eastward around Antarctica. It isolates Antarctica from warmer tropical waters, maintaining its cold climate. The ACC initiated around 34Ma.

The ACC amplified global cooling by strengthening Antarctic isolation, reducing heat transfer to the continent. This triggered the formation and expansion of the Antarctic ice sheet. It enhanced the separation of warm surface waters and cold deep waters, stabilizing the global climate and promoting cooler conditions.

Question 8

What ocean closed as India moved northwards?

Answer 8

Tethys Ocean

Question 9

When did ice sheets start to develop on Antarctica, and what plate tectonic occurrence (s) triggered this?

Answer 9

Around 34Ma, it was triggered by the opening of the Tasmanian Seaway and Drake Passage, which allowed the formation of the Antarctic Circumpolar Current (ACC)

Question 10

How did uplift of the Tibetan Plateau contribute to global cooling?

Answer 10

Increasing weathering rates, so higher elevations and exposed rocks accelerated the chemical weathering of silicate minerals, which drew CO₂ out of the atmosphere, acting as a long-term carbon sink, contributing to global cooling.

Question 11

When did ice sheets start to develop in the Northern Hemipshere, and what plate tectonic occurrences
triggered this?

Answer 11

Around 2.7Ma
The uplift of the Tibetan Plateau.
The closure of the Isthmus of Panama (3Ma), which altered ocean currents, particularly the Gulf Stream, and helped establish conditions conducive to the formation of ice sheets in the Northern Hemisphere.

Question 12

What is the Atlantic Meridonal Overturning Circulation, and what plate tectonic occurrence (s) triggered this and when?

Answer 12

The AMOC is an ocean current system that transports warm surface waters to the North Atlantic, where they cool, sink, and flow southward as deep water. The AMOC was triggered by plate tectonic events, including the opening of the Bering Strait (3Ma) and the closure of the Isthmus of Panama (3Ma).

Question 13

What is the age of the start of the Quaternary and what defines the start of the Quaternary?

Answer 13

The Quaternary Period began 2.58 million years ago. Its start is defined by the onset of the Pleistocene Ice Ages, marked by a significant global cooling and the expansion of large ice sheets in the Northern Hemisphere.

Question 14

What are the names of the two epochs of the Quaternary (and their ages)?

Answer 14

Pleistocene Epoch: 2.58 million to 11,700 years ago
Holocene Epoch: 11,700 years ago to the present.

Question 15

What records are used to create a high-resolution climatic record for the Quaternary?

Answer 15

Ice Cores, Sediment Cores, Tree Rings (Dendrochronology), Speleothems, Coral Reefs

Question 16

What events established the conditions for an abrupt shift into a state of widespread continental glaciation in the Quaternary?

Answer 16

Key events include the uplift of the Tibetan Plateau, which increased weathering and reduced CO₂, and the opening of the Bering Strait and Drake Passage, which altered ocean circulation, isolating Antarctica and strengthening the Antarctic Circumpolar Current.

Question 17

What is the basis for inferring palaeoclimate from oxygen isotopes?

Answer 17

Oxygen isotope ratios reflect past climate conditions. During colder periods, lighter ¹⁶O is preferentially stored in ice sheets, leaving seawater enriched in heavier ¹⁸O, which is recorded in marine microfossils and sediments.

Question 18

Are cooling phases associated with increases or decreases in 180 levels in sea water? How does sea level vary with oxygen isotopes?

Answer 18

Cooling phases are associated with increases in δ¹⁸O levels in seawater, as more ¹⁶O is trapped in ice sheets. Sea level is inversely related to δ¹⁸O: high δ¹⁸O indicates lower sea levels (glacial periods with extensive ice sheets), while low δ¹⁸O corresponds to higher sea levels (interglacial periods with reduced ice sheets).

Question 19

What two records is oxygen isotope data measured from?

Answer 19

Oxygen isotope data is measured from marine sediment cores (using the shells of microfossils like foraminifera) and ice cores (analyzing the isotopic composition of ancient snow and ice).

Question 20

Be familiar with the Marine Isotope Stage labelling system, e.g., is MIS17 a glacial or an interglacial? What drives Milankovic cycles? Over what periodicities do they occur? How do these relate to changes in the periodicity and amplitude of glacial-interglacial cycles before and after the EMPT?

Answer 20

The Marine Isotope Stage (MIS) system labels alternating warm (interglacial) and cold (glacial) periods based on oxygen isotope data. Even-numbered stages, such as MIS 18, are glacial, while odd-numbered stages, such as MIS 17, are interglacial.

Milankovitch cycles are driven by variations in Earth’s orbital parameters:

Eccentricity – changes in the shape of Earth’s orbit around the Sun.
Obliquity – changes in Earth’s axial tilt, affecting the intensity of seasons.
Precession – the wobble of Earth’s axis, altering the timing of seasons.

Before the Middle Pleistocene Transition (MPT) (1.2–0.7Ma), glacial-interglacial cycles were dominated by 41,000-year obliquity cycles with smaller ice volume fluctuations. After the MPT, 100,000-year eccentricity cycles became dominant, and glacial cycles increased in amplitude and duration. This shift likely reflects internal feedbacks, such as ice sheet dynamics and CO₂ changes, amplifying the climatic response to orbital forcing.

Question 21

What was the average length of glacial-interglacial cycles before the Early – Middle Pleistocene Transition and what has been the average length of glacial-interglacial cycles after it? Higher or lower amplitude?

Answer 21

Before the EMPT (1.2–0.7Ma), glacial-interglacial cycles averaged 41,000 years and a relatively lower amplitude. After the EMPT, the cycles lengthened to an average of 100,000 years and exhibited higher amplitude.

Question 22

After the Early – Middle Pleistocene Transition were warming phases of the glacial-interglacial cycle shorter or longer than cooling phases?

Answer 22

After the EMPT, warming phases of the glacial-interglacial cycle became shorter than cooling phases.

Question 23

When was the Last Glacial Maximum? What effect did it have on global sea level? What geomorphological features provide evidence of widespread glaciers?

Answer 23

The LGM occurred 26,500–19,000 years ago, when ice sheets were at their maximum extent. Global sea levels dropped by about 120–130 meters due to the vast amount of water locked in glaciers. Evidence includes moraines (deposits marking glacier edges), glacial striations (scratches on bedrock), U-shaped valleys, and drumlins (streamlined hills formed under glaciers).

Question 24

What is the age of the start of the Holocene? How abruptly did global temperatures rise and by how much?

Answer 24

11,700 years old, marking the end of the last glacial period. Global temperatures rose by about 4–5°C within a few thousand years, with some regions experiencing abrupt warming events over just a few decades. This rapid warming was driven by rising CO₂, changes in orbital configuration, and the collapse of large ice sheets, initiating the current interglacial period.

Question 25

When in the Holocene did eustatic sea levels approximately reach present day values?

Answer 25

Eustatic sea levels approximately reached present-day values around 7,000–6,000 years ago during the mid-Holocene.

Question 26

Why has eustatic sea level rise resulted in a relative sea level rise in some places and a relative sea level fall in others?

Answer 26

Eustatic sea level rise, caused by melting ice and thermal expansion of seawater, interacts with regional factors, leading to varying relative sea levels. In areas experiencing isostatic rebound (uplift of land after ice sheet melting), relative sea levels fall despite global sea level rise.

Question 27

What defines the Anthropocene? What evidence for it might there be in deposits? When did it begin?

Answer 27

The Anthropocene is a proposed epoch marked by significant human impact on Earth’s geology and ecosystems, including climate change, biodiversity loss, and widespread pollution. Evidence in deposits includes radioactive isotopes, plastics, carbon dioxide spikes, altered sediment layers, and anthropogenic fossils (e.g., domesticated plants and animals). It is often considered to have begun around the mid-20th century, during the Great Acceleration of human activity.