SLIDE 9 17 1st-person short stories
- 2. The last 65 million years
From dinosaurs to mammals
The dinosaurs were cold-blooded creatures & thrived in hot temperatures (a hothouse world); mammals are warm-blooded animals & thrive in cold temperatures (an icehouse world). The mammals became the dominant land animals after the extinc- tion of the dinosaurs at the end of the Cretaceous (65 myr). They have evolved to great diversity in a cooling world—through a drop of 20°C. If things return to the hothouse world of the dino- saurs, the mammals, including ourselves, will not survive.
10 20 30 40 50 5 4 3 2 1 Polar Ocean Equivalent ∆T(°C) 4 6 8 10 12
Ma 70 Ma
2 Equivalent Vostok ∆T(°C) Miocene Oligocene Eocene Paleocene Pleistocene Pliocene Cold Hot 60 56 20°C swing Paleocene Eocene Thermal Maximum
°C
Antarctic reglaciation Antarctic glaciation Antarctic thawing Eocene Optimum PETM 65,5 Cretaceous
5,5 Ma
Woolly mammoth
270-190 Ma 542 Ma– ca 2 Ma-12Ka
Antarctica
ca 34 Ma
Antarctica
pre 34 Ma
- 6. The last 350,000 years
Across the divide to Homo sapiens
On this graph, we home in on the last three major interglaci- al-glacial cycles. Each spanning ca 100,000 years and refmect- ing a swing of ca 10°C. Homo sapiens (anatomically modern humans) fjrst appeared somewhere, at around 200 ka, on the cooling curve from the interglacial MIS 7 to the glacial MIS 6. The compelling thing from this time on is how closely our major cultural breakthroughs—our genius moments—parallel the cli- mate curve. We will consider this further in the following graph.
200 ka
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 340 1 2 3 4 5 6 7 8 9 2.2 3.1 3.3 5.1 a b c d 5.2 5.3 5.4 5.5 6.2 6.3 6.5 a b c d e 7.1 7.3 7.5 a b c 8.2 8.3 8.5 9.1 9.3
ka
isotype stages 5 4 3 ice volume interglacial glacial 10°C swing
°C
320 Cold Hot 12 24
- H. sapiens
- H. neanderthalesis
Homo erectus
350,000 years ago
190
Pinnacle Point
Courtesy Curtis Marean Today 18,000 years ago Today Courtesy Richard Cowling 18,000 years
Glacials-interglacials
Our world is a hugely differ- ent place during glacial & in- terglacial epochs. At 18,000 years ago & at 135,000 years ago, the ice-caps were far more extensive than now; with the Arctic ice covering the greater part of North America and Western Europe.
Vegetation biomes
During intervals of maxi- mum glaciation, Africa was a parched and far grimmer place for humans to eke
- ut an existence. The Cape
coastal region would have been one of the few plac- es where the climate and food resources (terrestrial & marine) would have been manageable.
Sea-level fmuctuation
Hunter-gatherers occupying Pinnacle Point on the Cape coast during these same glacial & interglacial epochs, would have seen all-togeth- er different scenes—from landscape with a diversity of antelope to seascape with whales & seals. At 18 000 & again at around 138 000 years ago, the world was very different from how we know it today. The ice caps were far more extensive, the continental shelves largely exposed, the deserts way more expansive & the tropical forests much reduced.
Today 18,000 years ago
SHIFTING COASTLINES CHANGING CLIMATE
African vegetation
Expanded continental shelf with sea level ca 120 m lower than today; Southern Coastal Plain expanded by ca twice the area of the Kruger National Park Adopted from Compton (2011)
