|
Changes in Life Forms and the
Rise of Oxygen |
| Billions of
Years Ago |
What
Happened |
|
Oxygen in
Atmosphere |
| 4.6 |
Earth
formed |
|
Less than
1% pf [resent day levels |
| 3.5 |
Cyanobacteria appear |
|
|
| 2.3 |
Oxygen
accumulates rapidly Eukaryotes
with different types of cells appear. |
|
|
| 2.3 - 1.8 |
mitochondria appear Cell types
in eukaryotes increase |
Use oxygen
to create energy |
|
| 1.8 |
|
|
|
| 1.6
|
Plants and
animals separate |
|
15% of
present day levels & rising |
| 1.5 |
Some
eukaryotes had up to ten cell types
Plastids appear, enable cells to
produce oxygen through photosynthesis |
|
|
| 1
|
Some
eukaryotes have up to 50 cell types |
|
|
| 600 million
-- or maybe much earlier perhaps after plastids
emerged |
Cambrian
Explosion |
|
|
|
|
|
|
Hedges SB,
Jaime E Blair1, Maria L Venturi1
 and Jason L Shoe:
A molecular timescale of
eukaryote evolution and the rise of complex multicellular
life.
BMC
Evolutionary Biology 2004, 4:2
S Blair Hedges1
 , Jaime E Blair1
, Maria L Venturi1
and Jason L Shoe2
1NASA
Astrobiology Institute and Department of Biology, The
Pennsylvania State University, University Park, PA 16802,
USA
2Harvard School of Dental Medicine, 188 Longwood
Avenue, Boston, MA 02115, USA
BMC Evolutionary Biology 2004, 4:2
The electronic version of this article is the complete one
and can be found online at:
http://www.biomedcentral.com/1471-2148/4/2
|