Skip to content

Latest commit

 

History

History
35 lines (28 loc) · 1.74 KB

LabExercise16.md

File metadata and controls

35 lines (28 loc) · 1.74 KB

Periodicity in Sediments

In a seminal 1984 paper David M. Raup and J.J. Sepkoski detected a 27-million year periodicity in extinction rates (originally stated to be 26 Myr).

This finding sparked a lot of speculation that perhaps there was an extra-terrestrial mechanism (e.g., cosmic radition, impacts) that operated on a 27-million year cycle that was driving extinction patterns.

Let's take quick look at what the PBDB has to say about this finding.

Download paleobiology database data

Let's download two starting dataset from the paleobiology database and calculate extinction rates q across the Eocene-Oligocene mass extinction boundary.

# Load in the velocirpatr package

# Get that Eocene data
Eocene = velociraptr::downloadPBDB(Taxon="mammalia",StartInterval="Eocene",EndInterval="Eocene")

# Get that Oligocene data
Oligocene = velociraptr::downloadPBDB(Taxon="mammalia",StartInterval="Oligocene",EndInterval="Oligocene")

plot(f.data$freq[harmonics]*length(trajectory),

  •  f.data$spec[harmonics]/sum(f.data$spec), 
    
  •  xlab="Harmonics (Hz)", ylab="Amplitute Density", type="h")
    

library(GeneCycle)

f.data=GeneCycle::periodogram(SedimentExtinction) trajectory=SedimentExtinction[findPeaks(SedimentExtinction,"local_max")][which(SedimentExtinction[findPeaks(SedimentExtinction,"local_max")]>0.112994)]

findPeaks<-function(x,Model="all_min") {

  •     Peaks<-switch(Model,
    
  •             "all_min"=which(diff(c(FALSE,diff(x)>0,TRUE))>0),
    
  •            "local_min"=which(diff(diff(x)>0)>0)+1,
    
  •             "all_max"=which(diff(c(TRUE,diff(x)>=0,FALSE))<0),
    
  •             "local_max"=which(diff(diff(x)>=0)<0)+1
    
  •             )
    
  •     return(Peaks)
    
  •     }