Across
- 1. the process by which species adapt over time in response to their changing environment.
- 4. Any method of measuring the age of an event or object in years.
- 7. a major division of time that is a subdivision of an eon and is itself subdivided into periods.
- 8. form an imprint of an organism.
- 9. The process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element.
- 11. A method that provides objective age estimates for carbon-based materials that originated from living organisms. An age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against an internationally used reference standard.
- 13. The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock.
- 14. a type of fossilization that happens when minerals transported by water fill in all the open spaces of an organism or organic tissue. Within these spaces, mineral deposits form internal casts.
- 15. The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope.
- 16. Around 530 million years ago, a wide variety of animals burst onto the evolutionary scene
- 18. A method of determining the absolute age of an object by comparing the relative percentages of a radioactive parent isotope and a stable daughter isotope.
- 19. A fossil that is useful for dating and correlating the strata in which it is found.
- 22. an undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom.
- 23. event is when species vanish much faster than they are replaced. This is usually defined as about 75% of the world's species being lost in a short period of geological time - less than 2.8 million years.
- 24. The first 4 billion years, or 88 percent, of Earth's history, continents formed and our modern atmosphere developed, while early life evolved and flourished.
Down
- 2. A fossilized structure, such as a footprint or a coprolite, that formed in sedimentary rock by animal activity on or within soft sediment.
- 3. Divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet.
- 5. ancient group of photosynthetic microbes that occur in most inland waters
- 6. A rock that falls to Earth from space.
- 10. A period of time equal to one billion years.
- 12. Any method of determining whether an event or object is older or younger than other events or objects.
- 17. sometimes when an animal dies and its body decays, it can leave an imprint in the sediment. If this imprint fills in with minerals from sediment and groundwater, it can harden to form a fossil
- 20. a major division of time that is a subdivision of an Era and is itself subdivided into epoch.
- 21. A division of time that is a subdivision of a period and is itself subdivided into ages.