--- title: Deep time and the story of life — a lesson of Mova's school · trees and pragmatics description: «Deep time and the story of life», a lesson of the geography course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: The Earth is about 4.54 billion years old, a span so huge that geologists call it deep time. --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Geography](https://md.mova.elamur.ai/free/en/corpora/school/geography/) / Deep time and the story of life # Deep time and the story of life Lesson 58 of the geography course of Mova's primary school: 18 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/geography/58-deep-time-and-the-story-of-life/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/0/) — The Earth is about 4.54 billion years old, a span so huge that geologists call it deep time. - [1](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/1/) — If all of Earth's history were squeezed into one day, humans would appear only in the last few seconds before midnight. - [2](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/2/) — How do we know? - [3](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/3/) — Some atoms are radioactive and slowly change into other atoms at a steady rate, like sand falling through an hourglass. - [4](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/4/) — By measuring how much of each is in a rock, scientists can work out its age. - [5](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/5/) — For billions of years life was only microbes. - [6](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/6/) — Tiny sunlight-using microbes slowly filled the air with oxygen from about 2.4 billion years ago; about 540 million years ago animals with shells, eyes and legs burst onto the scene in the Cambrian explosion. - [7](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/7/) — Plants reached land, four-legged animals crawled out, and great disasters struck: about 252 million years ago about 90% of sea species died out, and about 66 million years ago an asteroid about 10 km wide hit Mexico and ended the non-bird dinosaurs, leaving room for mammals. - [8](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/8/) — The Earth is about 4.54 billion years old. - [9](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/9/) — Radioactive atoms decay into other atoms at a fixed rate, so measuring both tells the age of a rock; the time it takes for half of them to change is called a half-life. - [10](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/10/) — Earth's history is divided into eons, eras and periods, such as the Jurassic, about 200 to 145 million years ago, and the Cretaceous. - [13](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/13/) — About 540 million years ago, many animal groups with shells, eyes and legs appeared fairly quickly, in the Cambrian explosion. - [14](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/14/) — Plants moved onto land about 470 million years ago. - [15](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/15/) — The first four-legged animals crawled out of the water about 375 million years ago. - [16](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/16/) — The biggest mass extinction, about 252 million years ago, wiped out about 90% of sea species. - [17](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/17/) — About 66 million years ago an asteroid about 10 km wide hit Mexico and ended the age of non-bird dinosaurs. - [18](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/18/) — Mammals had lived as small animals beside the dinosaurs; after the dinosaurs, mammals spread into the empty places in nature and grew into many forms, from whales to elephants. - [19](https://md.mova.elamur.ai/free/en/corpora/school/geography/58-deep-time-and-the-story-of-life/19/) — Geologists call the vast span of Earth's history deep time, far longer than human history; humans appeared only about 300,000 years ago. - ← previous: [Fossils](https://md.mova.elamur.ai/free/en/corpora/school/geography/57-fossils/) - next →: [Coal, oil and gas](https://md.mova.elamur.ai/free/en/corpora/school/geography/59-coal-oil-and-gas/) - ↑ back to [Geography](https://md.mova.elamur.ai/free/en/corpora/school/geography/)