Why are my seedling's leaves yellow?

Well my one week old autoflower has gained its first set of leaves
one nice coloured green bladed ones
and another pair of rounded? leaves,
the problem is that the rounded ones are yellow / brown
i dont know if its fine as im first grower

TEMP - 70-80F
PH - 7.5-8
http://www.google.co.uk/imgres?imgurl=http://news.humcounty.com/images/marijuana_seedling.jpg&imgrefurl=http://news.humcounty.com/45_Pounds_is_a_LOT_of_Weed.html&usg=__5RxlLAyslISHn3668nZ7wmZyOLM=&h=471&w=500&sz=28&hl=en&start=0&zoom=1&tbnid=-InUJimKmY2dqM:&tbnh=131&tbnw=136&ei=loPqTd2qB8jKsgb6wZiBCQ&prev=/search%3Fq%3Dweed%2Bseedling%26um%3D1%26hl%3Den%26safe%3Doff%26sa%3DN%26biw%3D1280%26bih%3D709%26tbm%3Disch&um=1&itbs=1&iact=rc&dur=265&page=1&ndsp=28&ved=1t:429,r:2,s:0&tx=59&ty=63&biw=1280&bih=709
the vertical leaves on that are like mine, but yellowish brown
while other ones are healthy

cotyledon leaves are the small rounded leaves that are the first to sprout. They tend to die off sooner or later, how quickly I think is determined by the strain, soil conditions and amount of water available. As they supply the plant in it's early stages with extra water and nutrients. But I wouldn't be concerned, just the natural process.

Shadeslay said:

cotyledon leaves are the small rounded leaves that are the first to sprout. They tend to die off sooner or later, how quickly I think is determined by the strain, soil conditions and amount of water available. As they supply the plant in it's early stages with extra water and nutrients. But I wouldn't be concerned, just the natural process.

Click to expand...

what shadesley said is spot on.

Thanks guys much better than grasscity