Earth Science Lesson 1
The Solar System

Pre-Test
Q&A	History of the Earth

Instruction 1-4

The Solar Nebula/Earth's Formation from the Nebula | Cloud of Dust Theory | Formation and Origin of the Moon | Early Earth | The Sun | Effects of Asteroid Impacts in Shaping the Surface of Planets | Evidence for the Existence of Planets Orbiting Other Stars | Summary

Early Earth
http://www.ldolphin.org/Early.html

The Earth is very old. Scientists often describe it as being “more than 4-1/2 billion years old.” But they can be even more precise. Today, scientists think that the Earth is 4.6 billion years old. What makes them think so? Meteorites.

As Earth was being formed, it was constantly bombarded by meteorites. Meteorites were important in giving Earth its shape. And some of those meteorites are still with us today. Scientists can tell how old these meteorites are through a process called “age dating.” Age dating works like this:

Meteorites are rocks. Over time, certain atoms in rocks change into other atoms through radioactive decay. And since scientists can measure this process precisely, they can work out how many years it’s been since the rock was formed. It’s like measuring the rings of a tree to see how old it is. The oldest meteorites age-date at about 4.6 billion years – so that that’s how old the Earth is.

The history of the earth is divided into different Eons. These Eons are divided into eras, the eras are divided into periods, and the periods are divided into epochs. We’ll tell you a little - don’t worry, just a little - about each of them, but first take a look at this brief outline. Don’t try to memorize it -- it’s just a guide to what we’ll be talking about. 

The history of the Earth:

The Hadean Eon (4.6 to 3.8 billion years ago)
http://en.wikipedia.org/wiki/Hadean

The Hadean Eon was a violent, dangerous time. Earth was constantly being bombarded by meteorites. Its surface was hot and molten. At first, there was no atmosphere. Then, as things began to cool and the meteor bombardment slowed down, an atmosphere began to build. But it was a hot, poisonous, acidic atmosphere. There was no oxygen. Nothing could live there. This was no spot for vacation.

The Precambrian Eon (3.8 billion to 545 million years ago)
http://www.windows.ucar.edu/tour/link=/earth/past/Archean.html&edu=high

The Precambrian Eon  represents an incredible seven-eighths of the Earth’s history. We don’t know much about it. But what we do know is pretty dramatic.

The early part of The Precambrian Eon is called the Archean era. During this time, Earth changed radically. There was still no oxygen, but the climate cooled from blazing hot to warm. The atmosphere became less poisonous. The stage was set. We don’t know exactly when and where -- but this is when life began. Scientists think life began about 3.5 billion years ago.

Of course that life was very different from life today. The earliest forms of life are called prokaryotes. They were primitive bacteria. They were photosynthetic, which means they took in carbon dioxide (which the atmosphere was full of) and released oxygen. As more oxygen was released into the atmosphere, more advanced life forms could develop, although prokaryotes were still the only life form for close to 2 million years.

The next era in The Precambrian Eon is called the Proterozoic. During this period, huge deposits of iron occurred. Earth’s atmosphere changed as more oxygen built up and a new life form developed – eukaryotes. Originally, eukaryotes were one-celled algae, but they gradually evolved into more complicated life forms. Over time, eukaryotes spit into the two main categories of life on Earth today -- plants and animals.

The Phanerozoic Eon
http://www.palaeos.com/Timescale/Phanerozoic.htm

The Phanerozoic Eon began 545 million years ago – and we’re still in it. But here it gets a little complicated, because it’s divided up into so many different eras, periods and epochs. But bear with us – we’ll try to make it as simple as possible. After all, it’s millions of years and the whole history of the earth that we’re talking about.

The are three eras in The Phanerozoic Eon. They are:
    Paleozoic (545 - 245 million years ago)
    Mesozoic (245 - 65 million years ago)
    Cenozoic (65 million years ago up till today)

The Paleozoic era is divided into six periods:
    Cambrian period / Ordovician period / Silurian period /
    Denovian period / Carboniferous period / Permian period

Here are some of the most interesting things about each of those periods:

Cambrian. The Cambrian period is a very important time in the history of life on Earth. More life forms originated then than at any other time in history. Hard-shelled organisms developed, which means that we have an extensive fossil record. Life exploded in the sea: trilobites, sponges, snails, clams and corals. This was also when sex began, since prokaryotes were asexual. Differentiation of the sexes and sexual reproduction led to an amazing population explosion in all species. If you only remember one of the Paleozoic periods, the Cambrian is the one to remember.

Ordovician. The Ordovician period is when fish began to populate the seas.

Silurian. The Silurian period is when plants begin to populate the land. Scorpions crawled out of the sea. This is the golden age of fishes.

Devonian. The Devonian period is when fish crawled out of the sea, turning into
amphibians. Insects joined them. This is the time of spiders, scorpions and cockroaches – which will probably be with us forever. For the first time, plants with seeds developed (a sort of plant version of sex).

Carboniferous. During the Carboniferous period the climate turned very hot and Earth was covered with swamps, huge ferns and forests. Most of the coral on earth dates from this period. Early reptiles and winged insects developed. Amphibians ruled! The Carboniferous period is divided into two parts. These parts are based on regions of the United States where significant events took place. One is the Pennsylvanian (Upper Carboniferous) which is when and where most of our coal was formed. The other is the Mississippian (Lower Carboniferous), which is when and where most of our limestone comes from.

The Permian. The Permian period was when life on Earth experienced one of its most devastating extinctions. This happened because of something called “plate tectonics”. The surface of the earth is made up of six large “plates,” plus many smaller ones. As these plates shift and move, continents form and separate and the climate is drastically affected. During the Permian period, Earth’s plates moved in such a way that the Earth turned into an icehouse. Almost everything died. This is called The Permian Extinction. To learn more about plate tectonics, click: http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/introduction.html

The second era in the Phanerozoic Eon is called the Mesozoic era. It is divided into three periods. They are: Triassic / Jurassic and / Cretaceous.

During the Triassic period, Earth warmed up again and new life forms flourished. Reptiles and primitive mammals populated the planet. But the Triassic period ended with another severe extinction. Scientists think this happened some 200 million years ago.

This led to the next great period in Earth’s history, the Jurassic, and the rise of everybody’s favorite ancient animal – the dinosaur. Dinosaurs ruled the Earth for 150 million years, which is a pretty amazing achievement.

These dinosaurs were not purple and plush and they didn’t sing, so far as we know. And if you’ve seen the movie “Jurassic Park,” don’t worry – nobody is going to be creating real dinosaurs again anytime soon.

Birds also began during the Jurassic period and they are still with us. In fact, many scientists believe that birds are actually the descendants of dinosaurs.

The last period of the Mesozoic Era was called the Cretaceous period, which is when the first flowering plants appeared. But the whole Mesozoic era came to a crashing end - dinosaurs and all - when a gigantic meteor hit the Earth about 65 million years ago.

The final era of the Phanerozoic Eon is called the Cenozoic Era. There are two main periods within the Cenozoic era: the Tertiary period (65 – 1.6 million years ago) and the Quaternary period (1.6 million years ago up till today).

By the middle of the Tertiary period, all the major categories of mammals were already in existence, although there would still be much evolutionary development. Toward the end of this era, about 3 million years ago, our earliest ancestors, the hominids, appeared.

Lots of ocean-shelf deposits formed, creating at least half of the oil deposits we have today. Since the dinosaurs were gone, small mammals took over – tiny horses, for example, the size of modern dogs. These mammals evolved, becoming more and more specialized.

We human beings are mammals, which means that – like all mammals – we suckle our young from milk-producing modified sweat glands called mammaries (breasts). There was great diversification among these mammals and exotic large carnivores (meat eaters) roamed the earth.

The continents were shifting and changing, as they are still doing today. India and Australia broke away from Antarctic. India crashed into Asia and Australia remained isolated – which led to the development of many extraordinary plants and animals found only in Australia. Around 35 million years ago – again due to plate tectonics (which we discussed earlier) -- another ice age occurred. Again, very little life survived. Fortunately, our ancestors did.

The second period of the Cenozoic era is called the Quaternary period. It began 1.6 million years ago and we’re still in it today.

The Quaternary Period is divided into two epochs: the Pleistocene epoch and the Holocene epoch.

The Pleistocene epoch lasted from 1.6 million until 10,000 years ago. During this epoch, there were warmer and cooler times called glacial and interglacial periods. There have been 10 major glacial periods (ice ages) since Earth began. At the end of the Pleistocene epoch, there was a major extinction of large mammals. Were we humans to blame? We don’t know.

The current period of Earth’s development, the Holocene epic, began 10,000 years ago. We’re still in this epoch today. We are in an interglacial period, which means a warm climate with good conditions for life. Even so, plants and animals are disappearing at an alarming rate. Perhaps 25% of all living species on Earth will disappear within the next 30 years. Why? What is Earth’s future?

Just as we don’t know exactly when and where life began, we can’t know exactly what the future holds. Are there things we can do to ensure our future? This is a subject of much conversation and controversy.

There are a number of interesting web sites which will tell you more about Early Earth. One of them is

http://www.ucmp.berkeley.edu/help/timeform.html

Experiments for Home and Classroom
 

Finding a fossil is like visiting early Earth -- and you don't have to be a Paleontologist to find one. Anyone can do it if they go about it the right way. Here, from New York's American Museum of Natural History, is a complete student guide for finding and identifying fossils. Click: http://ology.amnh.org/paleontology/stuff/findfossils.html 

Most dinosaurs date from the Cretaceous Period, 145 million to 65 million years ago -- but dinosaur eggs are being found every day. National Geographic invites students to take part in an on-line Dinosaur Egg Hunt, which includes finding the eggs, seeing what's inside and watching them "hatch" (that's a virtual hatch, of course). Click: http://www.nationalgeographic.com/features/96/dinoeggs/intro.html 

The history of the Earth is divided into Eons, Eras, Periods and Epochs. By the Tertiary Period (65 million to 1.6 million years ago), all major forms of mammals had already appeared on Earth. Mammals have an amazing ability to adapt to cold water, which is thought to have contributed to their survival. Human beings are mammals, and this experiment allows students to demonstrate mammalian cold-water survival skill on themselves. This experiment should be done with a parent or teacher. Click:
http://ology.amnh.org/marinebiology/stufftodo/flow_main.html

Archeologists learn about the past from the artifacts people leave behind. In this activity, students are encouraged to make their own time capsule and fill it with artifacts that future archeologists might study. Click:  http://ology.amnh.org/archaeology/stufftodo/time_main.html 

All living things are made of cells -- and they have been ever since prokaryotes (primitive bacteria) arose about 3.5 billion years ago, during the Archean Era. But what makes each living thing unique? It's DNA -- the unique genetic code that's found in every cell. In this activity, students can made their own model of the famous DNA double helix. This activity is primarily designed for younger students (9th graders). Click:  http://ology.amnh.org/genetics/stufftodo/model.html 

Although not an experiment that students can repeat, this is one of the most famous -- and controversial -- experiments in the entire study of life on Earth. Many scientists endorse it, while others dispute its findings. In the 1950's, biochemists Stanley Miller and Harold Urey conducted an experiment in which they demonstrated that several organic compounds formed spontaneously when the conditions of Earth's early atmosphere were simulated in their laboratory. For a brief description of the Miller-Urey experiment, click:  http://www.windows.ucar.edu/tour/link=/earth/Life/miller_urey.html&edu=high

Now let's do Practice Exercise 1-4 (top)

Next Page:  Instruction, page 5 (top)