datelifeplot: Methods to plot chronograms

#' Table of geological ages and time including those preceding earth formation
#' Goldblatt et al. 2010 doi:10.5194/se-1-1-2010
#'
#' @name geostellar
#' @docType data
#' @format A data frame
#' @source \url{https://sites.google.com/site/geologicdatascale/timescale}
#' @keywords geologic time earth universe formation
#' @details
#' Generated with:
#'
#' geostellar <- read.csv(file = "inst/extdata/geo_stellar_chrono_scale_2018.9.20.csv")
#' utils::data(strat2012)
#' had <- strat2012[rep(116, each=6),]
#' rownames(had) <- 116:121
#' had$era <- c("Neohadean", "Mesohadean", "Palaeohadean")
#' had$period <- c("Prometean", "Acastan", "Procrustean", "Canadian", "Jacobian", "Hephestean")
#' had$MA <- c(3900, 4000, 4100, 4200, 4300, 4400)
#' chao <- strat2012[rep(116, each=4),]
#' rownames(chao) <- 122:125
#' chao$eon <- rep("Chaotian", 4)
#' chao$era <- c(rep("Neochaotian", 2), rep("Eochaotian", 2))
#' chao$period <- c("Titanomachean", "Hyperitian", "Erebrean", "Nephelean")
#' chao$MA <- c(4500, 4560, 4567, 4730)
#' usethis::use_data(geostellar)
#'
"geostellar"