744 Unit 5: The Changing Earth

Fossils are an important source of information about the history of life on Earth. The first observer to suggest thatfossils provided clues to the past was Xenophanes. He livedin Greece around 500 B.C. Today, knowledge about fossilshelps people find deposits of oil and understand changes in weather patterns. Above all, fossils reveal informationabout plants and animals that lived in the past.

The timeline shows a few events in the history of thestudy of fossils. Tools, such as radar and CT scanners thatwere invented for other purposes have helped scientistslearn more from fossils. The boxes below the timeline highlight the role of technology, along with applications of knowledge about fossils.

FOSSILSTHE STORY OF

1640 1660 1680 1700

EVENTS

APPLICATIONS ANDTECHNOLOGY

1669Scientist Notes Importance of Rock LayersDanish-born scientist

Nicolaus Steno recog-

nizes that sediments

form new layers of

rock on top of old

layers. Therefore,

digging down

provides a way

to move back in

time. Scientists

plan to build on

Steno’s discovery

to determine the

ages of fossils found

in rock layers.

This sandstone formation

in Utah displays layers of

sediment that were laid

down one on top of another.

APPLICATION

Mapping Earth’s LayersIn the late 1700s, the geologist William Smith helpedsurvey land for canals throughout England and Wales.As workers dug deeper into the ground, Smith noticedthat fossils always appeared in the same order. He usedthis information to create the first map showing thelocations of rock layers under surface soil. It waspublished in 1815. As people began to understandthe importance of rock layers, they collected moreinformation from projects that required digging.Maps showing this type of information becamemore detailed and more useful. Today, geologistscombine information collected in the field withdata from satellite images to create precisemaps of rock layers.

1824Geologist Identifies Bones from Extinct AnimalEnglish geologist William Buckland

concludes that a fossilized jawbone comes

from an enormous reptilelike animal that is

extinct. He names the animal Megalosaurus.

This is the first

dinosaur to be

given a scientific

name.

745

1720 1740 1760 1780 1800 1820 1840

1785New Theory Suggests Naturalnessof ChangeJames Hutton of Scotland revolutionizes

geology with his theory of uniformitari-

anism. He argues that volcanoes, erosion,

and other forces shaped Earth’s landscape

slowly over a very long period and con-

tinue to do so. Hutton’s ideas challenge the

belief that the landscape is the result of

sudden changes and one-time events.

His theory leads to a better understanding

of the vast ages of Earth and fossils.

1799Siberian Discovers Frozen MammothWhile hunting for ivory tusks in Siberia, a

man discovers a 37,000-year-old mammoth

frozen in ice. Unfortunately, before scientists

can study the five-ton animal, it thaws and

wild animals eat most of it. However, the

skeleton and bits of hair still provide clues

to Earth’s past.

This map, hand-painted

in 1815, was the first

to show locations of

rock layers.

746 Unit 5: The Changing Earth

1861Workers Uncover Bird FossilLaborers digging up limestone rock

in southern Germany find a fossil

that looks like a lizard with wings.

The fossil is about 150 million years

old—the oldest known one of a bird.

TECHNOLOGY

Chemist Creates New Time ScaleIn the 1890s, scientists studying radiation beganto understand the idea of half-life. The chemistB. B. Boltwood used half-life data to identifythe ages of various rocks and create a newgeologic time scale. The ages he calculatedwere in the hundreds of millions or even billions of years—far greater than the agesmany scientists had been using. The time scalecontinues to be modified as new technologiesallow for ever more precise measurements.

1923Dinosaur Eggs Show Link with BirdsResearchers in Mongolia

find a nest of

fossilized dinosaur

eggs. The eggs are

in a circle. This

fact suggests

that dinosaurs,

like modern

birds, moved

their eggs and

arranged their nests.

1860 1880 1900 1920 1940 1960 1980

1965Microfossils Cause SensationTwo new scientific papers focus attention on Earth’s earliest

life forms. In these papers scientists describe rocks from

Canada that contain microfossils of algae and fungi—traces

of life vastly older than any others yet found. These findings

trigger huge new efforts in scientific research on ancient life.

The half-life of

carbon 14 will be

used to calculate

the ages of the

samples this

researcher is

preparing.

Timelines in Science 747

Learn more aboutfossils.

RESOURCE CENTERCLASSZONE.COM

When did life begin on Earth? Fossils havehelped scientists answer this question. Manythink that the oldest fossils date from 3.5 bil-lion years ago. This date might be pushed backif new techniques identify even older fossils.Or the date might be pushed forward. Somescientists argue that the 3.5-billion-year-oldtraces in rocks are not really fossils at all.Rather, they argue, the traces are just signs ofchemical reactions that did not involve any living organisms.

Research on fossils also helps people evaluate the impact of human activity on theenvironment. For example, the fossil recordshows a pattern of warming and cooling inEarth’s history. Human activity, such as burningof coal and oil, has helped cause Earth to getwarmer over the past century. Further studiesof fossils will help people understand howmuch of this warming is normal and how much is a result of human action.

TECHNOLOGY

CT Scans Show That T. Rex Could SmellComputerized tomography (CT) scans are commonlyused in medicine to search inside human bodieswithout surgery. A CT scan of the skull of aTyrannosaurus rex known as Sue showed that it had a large area in its brain for smelling. Its sharp sense of smell, combined with its size and strength, made the tyrannosaur an effective hunter and scavenger.

2001Researchers Find Earliest MammalScientists in China

find the oldest known

mammal fossil. The 195-

million-year-old skull is

from an animal that

weighed just 2 grams—

less than the weight of a penny.

2000Dinosaur Heart Surprises ManyNorth Carolina scientists use a medical device

called a CT scanner to identify the first known

fossilized dinosaur heart. The heart surprises

those who thought all dinosaurs were cold-

blooded. Its structure suggests that the dinosaur

was warm-blooded.

2000

This skull is part of Sue’s

skeleton—the largest

and most complete

T. rex yet found.

Reliving HistoryGet permission to dig a hole outside.Dig down two feet or more. Draw a sketch showing the layers of soil.Add notes to describe any variationsthat are not clear in the sketch. Try to explain the differences younotice in the layers.

Writing About ScienceSuppose you are an archaeologist whohas made one of the fossil discoverieson the timeline. Write a speech toyour fellow scientists explaining theimportance of your discovery.