One of the latter is his observation that grasses are only 70 million years old, meaning that grassland animals are younger than that. He takes pains, therefore, to write with clarity about what is “directly observable from the fossil record,” allowing for a few alternate theories and surprises. The author recognizes that geologic time is mind-boggling given a record of life that stretches back 4 billion years and a planet another half-billion years older than that. He begins along the banks of the Thames, which “now enters the sea more than 100 miles south of where it used to flow” thanks to changing sea levels in times of glaciation and glacial melt: Britain was once a tropical swamp. A tour of the past worlds that the geological history of Earth reveals.īritish paleontologist and evolutionary biologist Halliday roams the globe to examine the geological maxim that Earth’s past is its present and future-that the processes that once placed the continents into a single supermass will do so again.
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