Journal Entry #4 – Earth ’ s History and Radiometric Dating

Journal Entry #4 – Earth’s History and Radiometric Dating

Anchorage to Homer(or a brief history of the Earth)

226 Miles

4.6 Billion years

Mile 54 – 3.5 billion years ago

• First prokaryotic cells

(Between girdwood and portage)

Mile 128 – 2 billion years ago

• Eukaryotic cells• Free oxygen in the

atmosphere

(Seward-Homer split)

Seward Homer

Mile 176 – 1 billion years ago

• Multi-cellular organisms

(Kasilof)

Mile 196 – 600 million years ago

• First animals

(Ninilchik)

Mile 202 – 500 million years ago

• Diversification of animals

(Cambrian explosion)• First land plants

Mile 207 – 400 million years ago

• First insects• First amphibians

(Happy Valley)

Mile 214 – 250 million years ago

• Dinosaurs!• First mammals

Anchor Point

Mile 223 – 65 million years ago

• End of the dinosaurs• Earliest primates

(Just outside of Homer)

Mile 225 – 20 million years ago

• Diversification and spread of primates

500 yds to go! – 6 million years ago

• Earliest hominids

Sometime around 5-7 million years ago…

Orrorin tugenensis (Kenya) Laetoli, Tanzania

500 ft! – 2 million years ago

• Beginnings of our genus Homo

• Earliest stone tools

~ 2.5 - 2 MA…appearance of

our genus, Homo (Africa)

“Turkana Boy” – WT 15000

ER – 3733 (Kenya)

ER – 1470 (Kenya)

Oldowan Stone Tools

50 feet from end of Homer Spit – 200,000 years ago

• Earliest anatomically modern humans