While the Earth is about 4.54 billion years old, all of human civilization has been compressed into a single geological epoch: the Holocene. This has been ongoing for about 11,500 years, predating the first Mesopotamian civilizations for which we have any evidence. Prior to the Holocene was the Pleistocene, which ended with the Younger Dryas cold spell. Actually, the Holocene exists more as a demarcation for the period of geologic time that has included human civilization than as an epoch with an independent definition.
Our best ice core samples extend back 650,000 years: about a third of the way into the Pleistocene, but just a tiny foray into geologic time. Pollen from Lake Tanganyika might take us through the Pliocene (Greek for ‘more new’) and into the Miocene (‘less new’). Perhaps some yet-unanticipated data source will be able to take us further still.
It is amazing what scientists are able to determine from inference and the meticulous collection of data: from the age of the universe to the evolutionary history of the planet.
Pleistocene Epoch: the sixth geological epoch of the Cenozoic Era. The Pleistocene occurred approximately 1.81 million to 10,000 years ago. This was mostly a time of world cooling punctuated by 3-4 major ice ages. Most human evolution took place during the Pleistocene.
Hear it pronounced
Universal Heritage
Timeline of the universe and everything
You mentioned an especially dramatic episode in this timescale earlier: the Permian-Triassic Extinction Event.
The Canadiann Sheild is a Pre-Cambrian craton!!!!!
The Younger Dryas is so called because it corresponds, in the pollen record from Europe, to the latest (i.e. youngest) appearance of the Dryas octopetala pollen, an alpine flower in regions that are now far from alpine. It marks a clear period towards the end of the last ice age when the warming trend of the deglaciation in Europe particularly was interrupted for a period of about 1300 years before it got going again. There were clear glacier advances during this time and the moraines can be seen very clearly all around Europe and Scandinavia.
Past reconstructions: problems, pitfalls and progress
Filed under:
* Paleoclimate
* Climate Science
Many people hold the mistaken belief that reconstructions of past climate are the sole evidence for current and future climate change. They are not. However, they are very interesting and useful for all sorts of reasons: for modellers to test out theories of climate change, for geographers, archaeologists and historians to examine the impact of climate on past civilizations and ecosystems, and for everyone to get a sense of what climate is capable of doing, how fast it does it and why.
The debate is just beginning — on the Cretaceous!
The Cretaceous is the time period from 145 million years ago up to the demise of the dinosaurs about 65 million years ago. The Eocene is a more recent period, from 56 million years ago to 34 million years ago. In between is the Paleocene, which is generally somewhat cooler than the late Cretaceous or mid Eocene. It has long been known that the polar climate — particularly the Arctic climate — was very different from today’s. Many lines of evidence indicate temperatures well above freezing, with little or no permanent land ice and infrequent or absent sea ice. Lemurs could live in Spitzbergen, and crocodiles on Hudson Bay, to name a few examples. Most evidence also points to an absence of ice in Antarctica as well. These Hothouse (or Super Greenhouse) climates have much warmer polar regions than is the case for today’s climate, and winters were evidently very mild. These hothouse climates are idealized as having been almost completely free of significant ice sheets on land and sea ice cover in the ocean. Hothouse climates pose a challenge to our understanding of climate in general, but more particularly they serve as a critical clue as to what surprises a high-CO2 world might have in store for us.
This is so because, at present, the only viable theory for Hothouse climates is that they come about as a result of elevated CO2 concentrations, which in turn are due to long term changes in the Earth’s carbon cycle. The CO2 theory has many problems, some of which I’ll discuss below, but no theory without elevated CO2 has been able to even come close to accounting for the Hothouse states. These climates would be just dandy as a natural test of the Earth’s sensitivity to long lived greenhouse gas concentrations were it not for one nasty fact: it is very, very difficult to get an accurate idea of how high the CO2 concentrations were so far back in time (see Crowley and Berner or Broadly Misleading on RC). For example, estimates for the Eocene range from values similar to modern CO2 concentrations all the way up to 15 times pre-industrial CO2. This unpleasantly large range represents uncertainties in the proxies used to estimate CO2 in the distant past. Various general circulation models can achieve largely ice-free polar conditions with CO2 between 4 and 8 times present concentrations, though even at those levels there are difficulties in accounting for the mildness of the winters. And up until recently it was thought that the tropical temperatures in such simulations were far warmer than reality — but more about that anon. ..
As a result, contemporary stratigraphers have set extraordinarily rigorous standards for the beatification of any new geological divisions. Although the idea of the “Anthropocene” — an Earth epoch defined by the emergence of urban-industrial society as a geological force — has been long debated, stratigraphers have refused to acknowledge compelling evidence for its advent.
At least for the London Society, that position has now been revised.
To the question “Are we now living in the Anthropocene?” the 21 members of the Commission unanimously answer “yes.” They adduce robust evidence that the Holocene epoch — the interglacial span of unusually stable climate that has allowed the rapid evolution of agriculture and urban civilization — has ended and that the Earth has entered “a stratigraphic interval without close parallel in the last several million years.” In addition to the buildup of greenhouse gases, the stratigraphers cite human landscape transformation which “now exceeds [annual] natural sediment production by an order of magnitude,” the ominous acidification of the oceans, and the relentless destruction of biota.
Arctic lakes help scientists understand climate change
(Flagstaff, Ariz. Sept. 4, 2009) —A clearer picture of climate change is emerging from the sediment drawn from the bottom of Arctic lakes.
An international team of scientists, led by Darrell Kaufman, a Northern Arizona University professor of geology and environmental science, recently completed a five-year study that places the recent warming in the context of long-term climate change.
Because this warming occurred abruptly during the 20th century while atmospheric greenhouses gases were accumulating, these findings provide additional evidence that humans are influencing climate.
The evidence was found by generating a 2,000-year-long reconstruction of Arctic summer temperature using natural archives of climate change from tree rings, glacier ice and mostly from lake sediments from across the Arctic, a region that responds sensitively to global changes.
“Our reconstruction shows that the last half-century was the warmest of the last 2,000 years,” Kaufman said. “Not only was it the warmest, but it reversed the long-term, millennial-scale trend toward cooler temperatures. The cooling coincided with the slow and well-known cycle in Earth’s orbit around the sun, and it should have continued through the 20th century.”
He said during the past few decades, the Arctic has warmed at two or three times the rate of the rest of the world, and this enhanced warming is expected to continue.