Read the summary and the most important questions on The Handy Dinosaur Answer Book | 9781578593262 | Patricia Barnes-Svarney; Thomas E Svarney

• 1 Forming Fossils

• 1.1 In the Beginning

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• How old is the oldest rock and mineral found on Earth?

  The oldest rock discovered on Earth, the Acasta gneisses found in the tundra in northwestern Canada near the Great Slave Lake, is about 4,03 billion years old.
  
  The oldest minerals yet found are 4,404 billion years old and were found in Western Australia. The minerals - zircon crystals - eroded from their original rock, and then were deposited in younger rock.

• What gases began to accumulate after Earth's crust finally solidified?

  As Earth's crust solidified, gases began pouring out of fissures and volcanoes, accumulating in the forming atmosphere. These same gases still emanate from modern volcanoes, and include:
  
  

  1. Carbon dioxide (CO2)
  2. Water vapor (H2O)
  3. Carbon monoxide (CO)
  4. Nitrogen (N2)
  5. Hydrogen chloride (HCl)

  
  
  As these gases interacted in the atmosphere, they combined to form hydrogen cyanide (HCN), methane (CH4), ammonia (NH4) and many other compounds. This atmosphere would be lethal to most present day life-forms. Fortunately for life on Earth, over the next two to three billion years the atmosphere continued to change until it reached close to its present composition.

• 1.2 Beginnings of Life

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• When did the basic form of life develop on Earth?

  It is thought that as far back as about 3,8 billion years ago, a basic form of life was present on Earth. This life took the form of tiny cells, which were surrounded by membranes to isolate and protect their interiors from the surrounding environment. The cells had a basic genetic system similar to those in modern cells, and this allowed the cells to self-replicate. We classify these earliest life-forms as prokaryotes, which include such organisms as bacteria and cyanobacteria.

• When did larger cells develop?

  Larger cells, classified as eukaryotes, began to develop approximately 1,5 to 1,9 billion years ago, according to the known fossil record. Before this time, rock layers contained only tiny prokaryotes, such as bacteria and blue-green algae.

• Did life develop more than just one time?

  Many scientists believe that life may have started over and over on Earth. They speculate that once life began - either around ocean vents and/or in the shallow seas - comets and asteroids would strike the planet, killing off all the beginning stages of life. This may have happened many times over millions of years, until life became stable enough to sustain and diversify itself. 

• When did the first true plants appear on land?

  Fossils called Cooksonia, found in Ireland, were probably the first ture macroscopic plants to colonize land about 425 million years ago. Other plants also appeared not long after, including flowerless mosses, horsetails, and ferns. They reproduced by throwing out spores or minute organisms that carried the genetic blueprint for the plant. The ferns eventually developed seeds, but this did not happen until about 345 million years ago. Vascular plants - those with roots, stems, and leaves - evolved about 408 million years ago.

• When did the first soft-bodied animals appear in the oceans?

  Fossils reveal that the first soft-bodied animals appeared about 600 million years ago in the oceans. They included a form of jellyfish, as well as segmented worms.

• When did the first primitive dinosaurs appear?

  The first primitive dinosaurs appeared about 230 million years ago. They were much smaller, and less fierce, than the Tyrannosaurus rex we often think of when someone mentions the "dinosaur."

• How long did it take for dinosaurs to evolve from the first land animals?

  The first larger land animals that would eventually lead to the appearance of dinosaurs evolved around 440 million years ago. Dinosaurs then evolved around 250 million years ago. Thus, it took about 190 million years for dinosaurs to appear after the first land animals. Remember, these numbers are based on the currently known fossil record, and could change if new fossils are found. 

• 1.3 Geologic Time

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• What is geologic time?

  Geologic time is the immense span of time that has elapsed since Earth first formed - almost 4,5 billion years ago - to recent times.