Tipping points - Lecture 5 (anthropocene and global TP)

what are the 7 key criteral to define and epoch

1. A principal correlation event (the ‘marker’) preserved within a geologic-forming material (traditionally rock but also ice, peat, corals, wood etc)

2. Other primary and secondary markers

3. A demonstrated regional and global correlation

4. Complete continuous sedimentation with sufficient thickness above and below the ‘marker’ to show there has been a long-term change

5. An exact location must be given

6. It has to be accessible

7. And there have to be provisions for protection and conservation

what is the k/t bounday

is arguably the fifth mass extinction in our planet’s history. This catastrophic event wiped out around threequarters of all species living at the time, including the dinosaurs. Early work showed the boundary was often made up of black marine clay with little to no fossils. Elemental concentrations were measured across the boundary. Iridium, for instance, was found to increase by up to 330 times the background level at the boundary. It was proposed that the only viable possibility was an asteroid impact, causing the end of the Jurassic and the extinction of the dinosaurs. Based on the amount of iridium they measured, the team estimated the asteroid would have been around 10 km across, and the impact crater would likely have been ten times the size.

how did they define the k-p boundayr

Defined at El Kef, Tunisia. •

• Marine sediments from what had been the seafloor around the time of this catastrophic event, including the thin black clay layer marking the boundary.

• The boundary is defined by the peak in the extraterrestrial element iridium.

• A global signal from the impact site in Mexico

how did they define the holocene

• scientists turned to ice coring the summit of the Greenland Ice Sheet. Even though the Holocene has been considered a Geological Epoch for hundreds of years, it was only formally described in 2010!

• It is defined as a big jump in oxygen isotopes, which are a proxy for temperature. This happened 11,650 years ago.

• At one and a half kilometres below the summit of the Greenland Ice Sheet, this isn’t what you’d call immediately accessible. You can’t just go to Greenland and readily see this part of the ice sheet. Remember this is one of the requirements for defining a GSSP. To address this requirement for formally defining the Holocene.

what is the golden spike

Crutzen suggested the make-up of the atmosphere, particularly carbon dioxide, as one of the ways to identify when the planet moved beyond what could be considered normal.