B2.6

?
When is it thought that life on Earth began - but why is it difficult to be sure?
We think life began 3-4 billion years ago but there's not much valid evidence
1 of 20
What are fossils?
Remains of organisms from thousands/millions of years ago
2 of 20
What are 4 ways that fossils can be formed?
1. Hard bits of animals that don't decay 2. When an animal/plant doesn't decay after death (e.g. no oxygen) 3. When harder parts are replaced by other minerals 4. Traces left behind (like footprints)
3 of 20
Why are there no fossils of the first organisms?
They were soft-bodied
4 of 20
Why are some fossils formed but never found?
They can be destroyed by geological activity
5 of 20
What can the fossil record help us to understand? Why is this understanding limited?
We can see how much organisms have changed since life first developed on Earth - but only small bits of skeleton/shells have been found
6 of 20
What animal has not changed much over the last million years and why?
Sharks - their environment hasn't changed much
7 of 20
How many species is it predicted that have existed since the beginning of life? How many are alive today?
4 billion - with just a few million alive today
8 of 20
What is extinction and what causes it?
Permanent loss off all members of a species caused when they can't cope with environmental changes
9 of 20
What are examples of condition changes that may begin the process of extinction?
New predators, diseases or more successful competitors
10 of 20
When we talk about climate change, what time-frame are we talking about?
Millions & billions of years
11 of 20
How many mas-extinctions have there been throughout history?
5
12 of 20
When and why did the dinosaurs become extinct?
65 million years ago after a giant asteroid hit the Earth, which caused fires and earthquakes, and material in the atmosphere covered the Sun. Plants struggled to survive and the drop in temperature caused a global winter
13 of 20
When do some UK scientists think the dinosaurs became extinct and why?
137 million years ago after melting sea ice caused a 9 degrees C temperature drop, after finding an unexpected change in fossils and minerals in Norway
14 of 20
What is thought to happen just after a mass extinction?
Evolution
15 of 20
What stages must a population go through before a new species is evolved?
1. Become isolated from others 2. Each side reproduces 3. Natural selection in different environments
16 of 20
What is geographical isolation?
When 2 populations become physically isolated by a physical feature e.g. a new mountain range
17 of 20
What does it mean when a species is endemic to an area?
It is found only in that place
18 of 20
What is speciation?
When part of a population becomes isolated and adapts to its new, very different environment
19 of 20
What must be no longer possible for speciation to occur?
Successful breeding with the other species
20 of 20

Other cards in this set

Card 2

Front

What are fossils?

Back

Remains of organisms from thousands/millions of years ago

Card 3

Front

What are 4 ways that fossils can be formed?

Back

Preview of the front of card 3

Card 4

Front

Why are there no fossils of the first organisms?

Back

Preview of the front of card 4

Card 5

Front

Why are some fossils formed but never found?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

Biology
science
See all Biology resources »See all Old and new species resources »