--- title: How old is it? Rock layers, rock clocks, amber and the long story of life — a lesson of Mova's school · trees and pragmatics description: «How old is it? Rock layers, rock clocks, amber and the long story of life», a lesson of the biology course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: Look at the stripes in a cliff: each stripe is a layer of mud, sand or ash that settled on top o --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-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/) / [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/) / How old is it? Rock layers, rock clock… # How old is it? Rock layers, rock clocks, amber and the long story of life Lesson 276 of the biology course of Mova's primary school: 16 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/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/0/) — Look at the stripes in a cliff: each stripe is a layer of mud, sand or ash that settled on top of the one before, like books piled on a desk, so the lowest layers are usually the oldest. - [1](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/1/) — To get real numbers, scientists use rock clocks: some rocks, especially volcanic ash, hold atoms that slowly turn into other atoms at a steady speed, and measuring how much has changed tells the age, like reading how far a candle has burnt down. - [2](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/2/) — If a fossil lies between two ash layers, one 67 and one 65 million years old, the animal lived in between. - [3](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/3/) — Squeeze Earth's 4.5 billion years into one day and the story is amazing: for most of the day life is only tiny microbes, dinosaurs arrive at about 10.40 at night, vanish at about 11.40, and people turn up a few seconds before midnight. - [5](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/5/) — Some rocks, especially volcanic ash, contain atoms that change into other atoms at a steady rate; measuring how much has changed dates the rock, and ash layers above and below a fossil give its age. - [6](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/6/) — Carbon dating works only for things that lived up to about 50,000 years ago, such as mammoths and old bones; dinosaurs are far too old for it, so other rock clocks are used. - [7](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/7/) — Amber is tree resin that hardened over millions of years; insects stuck in the sticky resin were sealed in, with tiny hairs and wing veins kept. - [8](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/8/) — DNA breaks down over time, and no dinosaur DNA has ever been found; the oldest DNA read so far is about 2 million years old, from soil in Greenland. - [9](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/9/) — If Earth's 4.5 billion years were one day, dinosaurs would arrive at about 10.40 at night, vanish at about 11.40, and humans would appear a few seconds before midnight. - [10](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/10/) — The oldest fossils are about 3.5 billion years old: stromatolites, mounds built by tiny microbes; living stromatolites still grow at Shark Bay in Australia. - [11](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/11/) — For billions of years, all life on Earth was microscopic. - [12](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/12/) — About 540 million years ago many kinds of animals with eyes, shells and legs appeared fairly quickly in the fossil record; this is called the Cambrian explosion, and strange animals like Anomalocaris and five-eyed Opabinia lived then. - [13](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/13/) — Trilobites were sea creatures with jointed legs and hard shells, distant cousins of crabs and insects; they lived for about 270 million years and had some of the first complex eyes, made of crystal. - [14](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/14/) — Tiktaalik was a 375-million-year-old fish with a neck, lungs and strong leg-like fins; scientists guessed which age of rock it should be in, searched, and found it in the Canadian Arctic. - [15](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/15/) — Sea fossils are found at the top of Mount Everest, because that rock formed under the sea and was pushed up as continents collided; mountains still rise a few millimetres a year. - [16](https://md.mova.elamur.ai/free/en/corpora/school/biology/276-how-old-is-it-rock-layers-rock-clocks-amber-and-the-long-story-of-life/16/) — About 250 million years ago the continents were joined in one land called Pangaea, which is why the same fossils are found in Africa and South America; continents drift a few centimetres a year, about as fast as fingernails grow. - ← previous: [Fossils: how a living thing turns to stone and how we dig it up](https://md.mova.elamur.ai/free/en/corpora/school/biology/275-fossils-how-a-living-thing-turns-to-stone-and-how-we-dig-it-up/) - next →: [DNA simply: the recipe in every cell](https://md.mova.elamur.ai/free/en/corpora/school/biology/277-dna-simply-the-recipe-in-every-cell/) - ↑ back to [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/)