history of our planet week 5.1 fire and ice

mammal radiation after K-Pg and PETM. This lecture: - Cenozoic climate and mammal diversification - The paleocene-eocene thermal maximum - Methane hydrates and climate change lessons - The origins of us

the cenozoic

The latest geologic era

Divided into periods:

Used to be tertiary and quaternary periods

Now Paleogene, Neogene, quaternary

Periods divided into epochs:

E.g. paleocene, Eocene

the cenozoic - mammals

 

Niches vacated by dinosaurs filled by mammals

Mammals go from 150g to 1kg within 1 Myr

Predominantly diversification within lineages

Remember 66ma = K-Pg – after this evolution and cological diversity happened rapidly

Was only non-avian dinosours extinct

the cenozoic - origin of placental mammal orders

The APP orders:

Even-toed ungulates (artiodactyla):Foregut digesters, Pigs, camels, ruminants

-   Odd toed ungulates (perissodactyla): Hindgut fermenters, Horses, zebras, rhinos

-   Primates: Lemurs, monkeys, apes

-  Led to humans. These things appear quite abruptly

PETM = paleocene-eocene thermal maximum

• spike in temp very important

Isotopes of oxygen:

Oxygen 16,   Oxygen 18

Oxygen 18 is heavier than oxygen 16

All mass of oxygen is in nucleus

Both of these are stable

Difference in mass can be used to infer what the temp of the earth was e.g.50-6-myr ago

Isotopes of oxygen: Oxygen 16

Protons: 8

Neutrons: 8

Atomic mass: 15.994

Isotopes of oxygen: Oxygen 18

Protons: 8

Neutrons: 10

Atomic mass: 17.999

How is temperature reconstructed:

Foraminifera – pin head single-celled protozoa (tiny organism lives in uppermost portions of the sea) whose shell is made of calcium carbonate (used in bio pump – some carbon used to build shell was previously in mineral form, Prev in air through that carbon silicate cycle). When die, fall out of photic area of sea onto sea floor sediments

Ratio of oxygen isotopes (oxygen 18 and oxygen 16) in their shells is sensitive to temperature and global ice volume

Decreasing temperature gives increasing change oxygen 18 (proportion of 18 O is going up) as increasing ice volume preferentially locks up oxygen 16 in ice sheets

difference

  δ¹⁸O a measure of the difference between the ratio of ¹⁸O to ¹⁶O in a ‘sample’, and in today’s oceans

δ¹⁸O a measure of how much more ¹⁸O there is in a sample, how ‘enriched’ the ¹⁸O sample is

seawater is approx:

99.8% ¹⁶O

0.2 % ¹⁸O

Remember 18oxygen is heavier

seawater is approx: - in glaciated world

16 O – more is evaporated as it Is most the ocean. Also as it is lighter, it evaporates more easily than 18 O- so the water that comes out of the sea int the clouds has got a different isotopic ratio of 16 to 18 O – so more 16 O gets held up on ice – essentially taking oxygen from sea and putting it onto massive ice sheets

this means depleting ocean store of 16 O

This change in ratio of 16 to 18O means can infer the forams – due to the oxygen it used and the mass

 

Cenozozoic co2 reconstruction:

The different proxies for CO2 are stating to agree better than they used to

Fossil stomata:

Density on leaf surface increases as CO2 declines (as plant evolves to undertake more gaseous exchange as co2 concentration declines)

Phytoplankton

Carbon isotope fractionation sensitive to CO2

Ancient soils (paleosols)

Carbon isotope fractionation sensitive to CO2e

Paleocene-eocene thermal maximum

Within 20,000 yrs – global temps increased by 5*C

Know it happened due to proxy records

Other things happened at the same time:

Ocean acidification:

Dissolution of carbonate sediments indicates rapid acidification of the ocean (<10,000 years) pH – reduces = more acidic. Roch carbonate sediments and ph. goes down – can chemically react with the carbonate sediments

Requires a large and fairly rapid release of ~2000 GtC into atmosphere to change ocean enough

Prominent clay layer above

Takes more than 10,000 years for carbonate deposition to recover

Carbon cycle perturbation:

Carbon isotope record shows two negative shifts in δ^13C each ~ 1 Kyr long and ~ 20 kyr apart

This requires the release of ^13C- depleted carbon from organic matter or methane

Less carbon is required if the source is more ^13C-depleted e.g. methane hydrates