LE1 – 06 – Life in Geological Time

Geological Time A system of chronological dating that relates geological strata (rock layers) to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.

How do we know about life on our planet? We use geological formations and fossils to help determine when and what type of organisms lived on our planet. Fossils are defined as: The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in a rock.

Fossils can form in several ways. 1. Permineralization occurs when minerals carried by water are deposited around a hard structure.

2. Natural cast forms when flowing water removes all of the original tissue, leaving an impression.

3. Trace fossils record the activity of an organism.

4. Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

5. Preserved remains form when an entire organism becomes encased in material such as ice.

Only a tiny percentage of living things became fossils. Specific conditions are needed for fossilization.

Nearly all fossils are formed in sedimentary rock. The sediments build up until they cover the organism’s remains. Minerals replace the organic matter or fill the empty pore spaces of the organism.

Section 1 The History of Life Fossil Evidence of Change Dating fossils Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.

Relative dating provides an accurate way to estimate the age of fossils. Relative dating estimates the time during which an organism lived. It compares the placement of fossils in layers of rock. Scientists infer the order in which species existed.

Relative Dating - Index fossils Index fossils are another tool to determine the age of rock layers. Index fossils can provide the relative age of a rock layer. existed only during specific spans of time occurred in large geographic areas Index fossils include fusulinids and trilobites.

Radiometric dating uses decay of unstable isotopes. Isotopes are atoms of an element that differ in their number of neutrons. neutrons protrons

Radiometric dating uses decay of unstable isotopes. Isotopes are atoms of an element that differ in their number of neutrons. A half-life is the amount of time it takes for half of the isotope to decay. By analyzing the amount of the isotope present in a sample, scientists can use the half life to determine the age of the sample

The geologic time scale organizes Earth’s history. The history of Earth is represented in the geologic time scale. 100 250 550 1000 2000 PRECAMBRIAN TIME Cyanobacteria This time span makes up the vast majority of Earth’s history. It includes the oldest known rocks and fossils, the origin of eukaryotes, and the oldest animal fossils.

The Geologic Time Scale Section 1 The History of Life Fossil Evidence of Change The Geologic Time Scale The geological time scale is a model that expresses the major geological and biological events in Earth’s history. The geologic time scale is divided into the Precambrian time and the Phanerozoic eon. Eras of the Phanerozoic eon include the Paleozoic, Mesozoic, and Cenozoic eras. Each era is divided into one or more periods.

Eras Eras last tens to hundreds of millions of years. consist of two or more periods

Periods & Epochs Periods last tens of millions of years. most commonly used units of time on time scale associated with rock systems. Epochs last several million years.

WHY DO WE HAVE DIFFERENT ERA’S? Image courtesy of the UC Museum of Paleontology Understanding Evolution: http://evolution.berkeley.edu." Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

See textbook resource folder Chapter 14 - Slide 12

Autotrophic prokaryotes enriched the atmosphere with oxygen. Section 1 The History of Life Fossil Evidence of Change – Summary of Eras 1. Precambrian Era Nearly 90 percent of Earth’s entire history, stretching from the formation of Earth to the beginning of the Paleozoic era about 542 million years ago Autotrophic prokaryotes enriched the atmosphere with oxygen.

1. PRECAMBRIAN ERA WHAT DO SCIENTISTS THINK WAS ALIVE WAY BACK THEN?? BACTERIA THIS ERA LASTED FOR BILLIONS OF YEARS UNTIL MORE LIVING ORGANISMS EVOLVED Dr Tom Tregenza © Tom Tregenza Dr Gordon Beakes © University of Newcastle upon Tynelicensed IMAGES for use through the Centre for Bioscience ImageBank,http://www.bioscience.heacademy.ac.uk/imagebank/" Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

2. Paleozoic Era – “Ancient Life” Section 1 The History of Life Fossil Evidence of Change – Summary of Eras 2. Paleozoic Era – “Ancient Life” The ancestors of most major animal groups diversified in what scientists call the Cambrian explosion. Life in the oceans continued to evolve at the end of the Cambrian period. Fish, land plants, and insects appeared during the Ordovician and Silurian periods. The first tetrapods emerged in the Devonian.

www.carnegiemnh.org/ip/tours/virtual/hall.htm Image courtesy of the UC Museum of Paleontology Understanding Evolution: http://evolution.berkeley.edu." Image courtesy of the UC Museum of Paleontology Understanding Evolution: http://evolution.berkeley.edu." Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Between 60 and 75 percent of the species alive went extinct. Section 1 The History of Life 2. Paleozoic Era A mass extinction ended the Paleozoic era at the end of the Permian period. Between 60 and 75 percent of the species alive went extinct.

3. Mesozoic Era – “Middle Life” Section 1 The History of Life Fossil Evidence of Change – Summary of Eras 3. Mesozoic Era – “Middle Life” Mammals and dinosaurs first appeared late in the Triassic period, and flowering plants evolved from nonflowering plants. Birds evolved from a group of predatory dinosaurs in the middle of the Jurassic period. About 65 million years ago, a meteorite struck Earth.

http://geology.utah.gov/utahgeo/dinofossil/dinoage.htm Image courtesy of the UC Museum of Paleontology Understanding Evolution: http://evolution.berkeley.edu." Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Section 1 The History of Life Mesozoic Era – Continental Drift Plate tectonics describes the movement of several large plates that make up the surface of Earth. These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

Section 1 The History of Life

4. Cenozoic Era – “Recent Life” Section 1 The History of Life Fossil Evidence of Change – Summary of Eras 4. Cenozoic Era – “Recent Life” Mammals became the dominant land animals. After the mass extinction at the end of the Mesozoic era, mammals of all kinds began to diversify.