520 Unit 4: Life Over Time

How do scientists know about life on Earth millions ofyears ago? They dig, scratch, and hunt. The best cluesthey find are hidden in layers of rock. The rock-lockedclues, called fossils, are traces or remains of livingthings from long ago. Some fossils show the actual bodies of organisms, while others, such as footprints,reveal behavior.

Before 1820, most fossil finds revealed the bodiesof ocean life. Then large bones of lizardlike walking ani-mals began turning up, and pictures of a new “terriblelizard,” or dinosaur, took shape. Later, discoveries oftracks and nests showed behaviors such as flocking andcaring for young. Even today, discoveries of “living fossils,” modern relatives of prehistoric species, haveoffered us a rare glimpse of the activity of early life.

UnearthedLIFE

1800 1810 1820

EVENTS

APPLICATIONS AND TECHNOLOGY

1824

Giant Lizards from Fragments

William Buckland describes Megalosaurus, a giant

crocodilelike animal he studies from only a few bits

of jaw, teeth, ribs, pelvis, and one leg. A year later

Gideon Mantell assembles Iguanodon, a similar

animal, from fossil bones.

TECHNOLOGY

Removing Fossils with Care

The technology for removing fossils from rock beds has not changed muchsince the 1820s. Collectors still work by hand with hammers, chisels, trowels,dental picks, and sieves. Gideon Mantell used these when he chiseled out

Iguanodon bones embedded in one large rock called the “Mantle piece.”

Fossil hunters also use hand lenses and microscopes. Sometimes aprotective layer is built up with glue, varnish, or another finish.

For larger samples, a plaster cast often supports the fossil.Most fossils are packed using a technology found in anykitchen—a sealable plastic bag.

1938

African FishermanHauls in History

A South African fisherman

pulls up a five-foot fish he has

never seen. He calls the local museum,

whose curator, a naturalist, has also never seen the species. To

her surprise, biologists identify it as a coelacanth, a prehistoric

fish thought to be extinct for more than 50 million years.

1944

New Dawn for the DawnRedwood

Beside a small temple, a

Chinese scientist discovers

the dawn redwood, or

metasequoia, growing.

Common in fossil specimens

100 million years old, the tree

had not been seen alive in

recorded history. The 1944 find starts a

search, and in 1948, scientists find a small wild grove in

China as well.

APPLICATION

Protecting Fossils and Dig Sites

The United States Antiquities Act of 1906 preserves and protects historic and prehistoric sites. The act requires collectors to have a permit to dig for or to pick up fossils on public lands such as national parks. It also requires that any major find be publicly and permanently preserved in a museum.

The United Nations also now designates World Heritage sites.For example, the original Burgess Shale find in Yoho NationalPark in Canada is now protected by international law. Since1906, many states and provinces in Canada have enactedtheir own laws about land rights and the excavation and transport of fossils.

1900 1910 1920 1930 1940

1909

Burgess Shale Shows Soft Bodies

In the Burgess Pass of the Canadian Rocky

Mountains, Charles Walcott finds fossils preserved

in shale, a soft rock that preserves lacelike details

such as the soft tissues of the Marella. The glimpse

of life 505 million years ago is the earliest yet seen.

Timelines in Science 521

TECHNOLOGY

How Old Is a Fossil?

Before 1947, scientists used a method of fossil dating calledrelative dating. They assigned a date to a fossil according tothe rock layer in which it was found. The deeper, or older, thelayer, the older the fossil.

The discovery of radiometric dating in 1947 marked the firsttime a fossil’s date could be pinpointed. Organic matter decaysat a constant rate. So, by measuring the rate of decay, you cantell the age of the matter. Radiocarbon 14 is used to tell theage of a fossil that is less than 10,000 years old. Since most fossils are older than that, scientists use other methods.

Potassium-argon decays more slowly than carbon. It is a morecommon method of dating. All types of fossil dating have margins of error, or limits to accuracy.

522 Unit 4: Life Over Time

1953

Piltdown Man No Neanderthal

Scientists once applauded the discovery in 1912 of a

“Neanderthal skull” in the Piltdown gravel pit, but a

few had their doubts. In 1953, radioactive potassium

dating proves the Piltdown man to be nothing more

than the jaw of an orangutan placed beside human

skull fragments.

1990

Largest Tyrannosaurus, “Sue”

Out on a walk with her dog in the South Dakota bad-

lands, amateur fossil hunter Sue Hendrickson

discovers three huge bones jutting out of a cliff.

Hendrickson finds the largest and most complete

T. rex skeleton yet. The

67-million-year-old “Sue”

is now on display in

the Field Museum in

Chicago, Illinois.

1950 1960 1970 1980 1990

1974

“Lucy” and Upright KinFound

Digging in Ethiopia, Donald

Johanson finds an almost com-

plete hominid skeleton. He names

the fossil “Lucy,” after a Beatles

song. Lucy is over 3 million years

old, is three and one-half feet

tall, and has an upright stance or

posture. A year later, Johanson’s

crew finds “The First Family,” a

group of 13 skeletons of the

same species as Lucy.

Technology is sure to play a role in future fossil finds. Scientists can communicate vialaptop computers and satellites, which allowthe public to follow excavations as they occur.

Computer modeling helps scientists deter-mine what incomplete skeletons looked like. Italso helps them determine how dinosaurs andother living things once moved. Fossil findscan be combined with digitized informationabout modern living organisms and aboutenvironmental conditions. The model can testhypotheses or even help to formulate them.

Another area of technology that maybecome increasingly applied to fossils is DNAtesting to identify and help date fossils. This ismore complicated in fossilized bone, as thegenetic material can be fragmented. But withtime, scientists may discover new techniques toextract better genetic information. DNA is alsothe basis for cloning, which as yet can only beapplied to living organisms. Perhaps in thefuture it can be applied to preserved remains.

Timelines in Science 523

TECHNOLOGY

Fossil Classification and DNA

There are many ways to classify fossils. Scientists lookat bone structure, body posture, evidence of behavior,and environment. Microscopes are used to identifyorganisms too small for the eye to see. Study of DNAmolecules helps to identify species when soft tissuesremain intact, such as in fossils formed in amber orcrystallized tree sap. In 1985, polymerase chain reac-tion (PCR) became the simplest method to study theDNA extracted from fossils. In PCR, parts of DNA canbe copied billions of times in a few hours.

2000

1993

Oldest Fossils Are Too Small to See

Fossils discovered up to this point date back about 550

million years, to the dawn of the Cambrian Period.

J. William Schopf identifies fossils of microorganisms sci-

entifically dated to 3.4 billion years ago. This startling find

near Australia’s Marble Bar opens up a vast period of time

and once again reshapes theories about life’s beginnings.

Discover moreabout the latest fossil and living-fossil finds.

RESOURCE CENTERCLASSZONE.COM

Writing About Science:Film ScriptWrite your own version of the storyof life on Earth. Include drawings,photographs, or video clips to illustrate your story.

Reliving HistoryThink about the equipment archae-ologists and paleontologists use onexcavations. Think about their goals.Write a proposal to a local universityor museum asking them to fundyour excavation.