Early Earth Guided Notes Introduction

Earth Forms Scientists hypothesize that Earth formed about 4.6 billion years ago. They also believe that Earth started as a ball of dust, rock, and ice in space, pulled together by gravity.

Earth’s Surface Forms We call the first 100 million years the Precambrian Time, when the atmosphere, oceans, and continents began to form.

Atmosphere Earth’s first atmosphere was hydrogen and helium. It left after a huge collision with Earth and another object. Our second atmosphere consisted of carbon dioxide, water vapor and nitrogen.

Compare and Contrast the three atmospheres 1st 2nd 3rd Hydrogen CO2 (90) Nitrogen(78) Helium Nitrogen (5) Oxygen(21) Other (2) Other gases(1) Sulfur Dioxide(3) Put these into the bubbles in your notes!

The Oceans Too hot at first for liquid oceans, most water evaporated into water vapor. Then would condense to form rain, which would help to cool the Earth.

The Continents Earth’s rock started to cool and harden to form the continents.

Continental Drift The continents of the Earth moved very slowly over Earth’s surface About 2 cm per year

Life Develops Scientists can not pinpoint when or where life began. They have found fossils of single-celled organisms in rocks that formed about 3.7 billion years ago. These earliest life forms were probably similar to present-day bacteria. (Scientists Say Canadian Bacteria Fossils May Be Earth’s Oldest at 3.7 bya – Pictured below)

Paleozoic Era At the beginning of the Paleozoic Era, a great number of different kinds of organisms evolved. Scientists call this the Cambrian Explosion. Most of these animals were invertebrates, lacking a backbone.

Paleozoic Era During this time, jawless fishes evolved. Jawless fishes were the first vertebrates, animals with a backbone. Later on- animals reach land. Mass extinction ends the Paleozoic Era, killing plants, animals, and trees on land and in the ocean. Scientists do not know what caused this.

Pangaea About 260 million years ago, Earth’s continents moved together to form a great landmass, or supercontinent. One theory as to the mass extinction is that the climate change of Pangaea, might have caused some of the animals to die.

Mesozoic Era Reptiles were so successful during the Mesozoic Era that this time is often called the Age of the Reptiles. Mammals first appeared. Dinosaurs ruled the earth. Another mass extinction about 65 million years ago ends the Cretaceious Period.

Mesozoic Era Scientists believe that this extinction was caused by an object hitting the Earth.

Cenozoic Era Age of Mammals The extinction of dinosaurs created an opportunity for mammals. During this era, mammals evolved to live in many different environments- on land, in water, and even in the air. Ice age occurs when Earth starts to cool.

Geological Time Era A major division of time into three parts between the Precambrian and the present. Period One of the units of geological time into which geologists divide an Era.

Geological Time Epoch A unit of geological time that is a division of a period. Eon Divisions in the geological time scale that is billions and millions of years long.